Merge pull request #506 from bonk-dev/s5-date

Add support for reading/writing the legacy DATE (IEC date) datatype

.github/workflows/dotnet.yml

@@ -0,0 +1,134 @@
+# yaml-language-server: $schema=https://json.schemastore.org/github-workflow.json
+
+name: .NET
+
+on:
+  workflow_dispatch: # Allow running the workflow manually from the GitHub UI
+  push:
+    branches:
+      - 'main'       # Run the workflow when pushing to the main branch
+  pull_request:
+    branches:
+      - '*'          # Run the workflow for all pull requests
+  release:
+    types:
+      - published    # Run the workflow when a new GitHub release is published
+  
+env:
+  DOTNET_SKIP_FIRST_TIME_EXPERIENCE: 1
+  DOTNET_NOLOGO: true
+  NuGetDirectory: ${{ github.workspace}}/nuget
+
+defaults:
+  run:
+    shell: pwsh
+
+jobs:
+  create_nuget:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+      with:
+        fetch-depth: 0 # Get all history to allow automatic versioning
+
+    - name: Install GitVersion
+      uses: gittools/actions/gitversion/setup@v0
+      with:
+        versionSpec: '6.x'
+        includePrerelease: true
+        preferLatestVersion: true
+    
+    - name: Determine Version
+      id:   gitversion
+      uses: gittools/actions/gitversion/execute@v0
+
+    - name: Setup .NET
+      uses: actions/setup-dotnet@v3
+
+    - run: >
+        dotnet pack
+        --configuration Release
+        /p:AssemblyVersion=${{ steps.gitversion.outputs.assemblySemVer }}
+        /p:FileVersion=${{ steps.gitversion.outputs.assemblySemFileVer }}
+        /p:InformationalVersion=${{ steps.gitversion.outputs.informationalVersion }}
+        /p:PackageVersion=${{ steps.gitversion.outputs.semVer }}
+        --output ${{ env.NuGetDirectory }}
+
+    - uses: actions/upload-artifact@v3
+      with:
+        name: nuget
+        if-no-files-found: error
+        retention-days: 7
+        path: |
+          ${{ env.NuGetDirectory }}/*.nupkg
+          ${{ env.NuGetDirectory }}/*.snupkg
+
+  run_test:
+    name: test-${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    env:
+      configuration: Release
+      artifacts: ${{ github.workspace }}/artifacts
+    strategy:
+      matrix:
+        os: [windows-latest, ubuntu-20.04, macos-latest]
+      fail-fast: false
+
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Install Snap7 Linux
+        if: ${{ matrix.os == 'ubuntu-20.04' }}
+        run: |
+          sudo add-apt-repository ppa:gijzelaar/snap7
+          sudo apt-get update
+          sudo apt-get install libsnap7-1 libsnap7-dev
+          
+      - name: Install Snap7 MacOs
+        if: ${{ matrix.os == 'macos-latest' }}
+        run: |
+          brew install snap7
+
+      - name: Setup Dotnet
+        uses: actions/setup-dotnet@v3
+        with:
+          dotnet-version: |
+            6.x
+            7.x
+          
+      - name: Nuget Cache
+        uses: actions/cache@v3
+        with:
+          path: ~/.nuget/packages
+          # Look to see if there is a cache hit for the corresponding requirements file
+          key: ${{ runner.os }}-nuget-${{ hashFiles('**/packages.lock.json') }}
+          restore-keys: |
+            ${{ runner.os }}-nuget
+        
+      - name: Test
+        run: dotnet test --nologo --verbosity normal --logger GitHubActions
+
+  deploy:
+    # Publish only when creating a GitHub Release
+    # https://docs.github.com/en/repositories/releasing-projects-on-github/managing-releases-in-a-repository
+    # You can update this logic if you want to manage releases differently
+    if: github.event_name == 'release'
+    runs-on: ubuntu-latest
+    needs: [ create_nuget, run_test ]
+    steps:
+      - uses: actions/download-artifact@v3
+        with:
+          name: nuget
+          path: ${{ env.NuGetDirectory }}
+
+      - name: Setup .NET Core
+        uses: actions/setup-dotnet@v3
+
+      # Publish all NuGet packages to NuGet.org
+      # Use --skip-duplicate to prevent errors if a package with the same version already exists.
+      # If you retry a failed workflow, already published packages will be skipped without error.
+      - name: Publish NuGet package
+        run: |
+          foreach($file in (Get-ChildItem "${{ env.NuGetDirectory }}" -Recurse -Include *.nupkg)) {
+              dotnet nuget push $file --api-key "${{ secrets.NUGET_APIKEY }}" --source https://api.nuget.org/v3/index.json --skip-duplicate
+          }

GitVersion.yml

@@ -1,21 +0,0 @@
-assembly-informational-format: '{NuGetVersion}'
-mode: ContinuousDeployment
-branches:
-  master:
-    tag: rc
-    increment: Minor
-  feature:
-    regex: features?[/-]
-    tag: rc-{BranchName}
-    increment: Minor
-  pull-request:
-    regex: (pull|pull\-requests|pr)[/-]
-    tag: rc-pr-{BranchName}
-    increment: Minor
-  hotfix:
-    regex: hotfix(es)?[/-]
-    tag: rc
-    increment: Patch
-  develop:
-    regex: dev(elop)?(ment)?$
-    tag: b

S7.Net.UnitTest/CommunicationTests/Clock.cs

@@ -0,0 +1,259 @@
+using System;
+using System.Net;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using S7.Net.Protocol;
+
+namespace S7.Net.UnitTest.CommunicationTests;
+
+[TestClass]
+public class Clock
+{
+    [TestMethod, Timeout(1000)]
+    public async Task Read_Clock_Value()
+    {
+        var cs = new CommunicationSequence
+        {
+            ConnectionOpenTemplates.ConnectionRequestConfirm,
+            ConnectionOpenTemplates.CommunicationSetup,
+            {
+                """
+                    // TPKT
+                    03 00 00 1d
+
+                    // COTP
+                    02 f0 80
+
+                    // S7 read clock
+                    // UserData header
+                    32 07 00 00 PDU1 PDU2
+                    // Parameter length
+                    00 08
+                    // Data length
+                    00 04
+
+                    // Parameter
+                    // Head
+                    00 01 12
+                    // Length
+                    04
+                    // Method (Request/Response): Req
+                    11
+                    // Type request (4...) Function group timers (...7)
+                    47
+                    // Subfunction: read clock
+                    01
+                    // Sequence number
+                    00
+
+                    // Data
+                    // Return code
+                    0a
+                    // Transport size
+                    00
+                    // Payload length
+                    00 00
+                """,
+                """
+                    // TPKT
+                    03 00 00 2b
+
+                    // COTP
+                    02 f0 80
+
+                    // S7 read clock response
+                    // UserData header
+                    32 07 00 00 PDU1 PDU2
+                    // Parameter length
+                    00 0c
+                    // Data length
+                    00 0e
+
+                    // Parameter
+                    // Head
+                    00 01 12
+                    // Length
+                    08
+                    // Method (Request/Response): Res
+                    12
+                    // Type response (8...) Function group timers (...7)
+                    87
+                    // Subfunction: read clock
+                    01
+                    // Sequence number
+                    01
+                    // Data unit reference
+                    00
+                    // Last data unit? Yes
+                    00
+                    // Error code
+                    00 00
+
+                    // Data
+                    // Error code
+                    ff
+                    // Transport size: OCTET STRING
+                    09
+                    // Length
+                    00 0a
+
+                    // Timestamp
+                    // Reserved
+                    00
+                    // Year 1
+                    19
+                    // Year 2
+                    14
+                    // Month
+                    08
+                    // Day
+                    20
+                    // Hour
+                    11
+                    // Minute
+                    59
+                    // Seconds
+                    43
+                    // Milliseconds: 912..., Day of week: ...4
+                    91 24
+                """
+            }
+        };
+
+        static async Task Client(int port)
+        {
+            var conn = new Plc(IPAddress.Loopback.ToString(), port, new TsapPair(new Tsap(1, 2), new Tsap(3, 4)));
+            await conn.OpenAsync();
+            var time = await conn.ReadClockAsync();
+
+            Assert.AreEqual(new DateTime(2014, 8, 20, 11, 59, 43, 912), time);
+            conn.Close();
+        }
+
+        await Task.WhenAll(cs.Serve(out var port), Client(port));
+    }
+
+    [TestMethod, Timeout(1000)]
+    public async Task Write_Clock_Value()
+    {
+        var cs = new CommunicationSequence
+        {
+            ConnectionOpenTemplates.ConnectionRequestConfirm,
+            ConnectionOpenTemplates.CommunicationSetup,
+            {
+                """
+                    // TPKT
+                    03 00 00 27
+
+                    // COTP
+                    02 f0 80
+
+                    // S7 read clock
+                    // UserData header
+                    32 07 00 00 PDU1 PDU2
+                    // Parameter length
+                    00 08
+                    // Data length
+                    00 0e
+
+                    // Parameter
+                    // Head
+                    00 01 12
+                    // Length
+                    04
+                    // Method (Request/Response): Req
+                    11
+                    // Type request (4...) Function group timers (...7)
+                    47
+                    // Subfunction: write clock
+                    02
+                    // Sequence number
+                    00
+
+                    // Data
+                    // Return code
+                    ff
+                    // Transport size
+                    09
+                    // Payload length
+                    00 0a
+
+                    // Payload
+                    // Timestamp
+                    // Reserved
+                    00
+                    // Year 1
+                    19
+                    // Year 2
+                    14
+                    // Month
+                    08
+                    // Day
+                    20
+                    // Hour
+                    11
+                    // Minute
+                    59
+                    // Seconds
+                    43
+                    // Milliseconds: 912..., Day of week: ...4
+                    91 24
+                """,
+                """
+                // TPKT
+                    03 00 00 21
+
+                    // COTP
+                    02 f0 80
+
+                    // S7 read clock response
+                    // UserData header
+                    32 07 00 00 PDU1 PDU2
+                    // Parameter length
+                    00 0c
+                    // Data length
+                    00 04
+
+                    // Parameter
+                    // Head
+                    00 01 12
+                    // Length
+                    08
+                    // Method (Request/Response): Res
+                    12
+                    // Type response (8...) Function group timers (...7)
+                    87
+                    // Subfunction: write clock
+                    02
+                    // Sequence number
+                    01
+                    // Data unit reference
+                    00
+                    // Last data unit? Yes
+                    00
+                    // Error code
+                    00 00
+
+                    // Data
+                    // Error code
+                    0a
+                    // Transport size: NONE
+                    00
+                    // Length
+                    00 00
+                """
+            }
+        };
+
+        static async Task Client(int port)
+        {
+            var conn = new Plc(IPAddress.Loopback.ToString(), port, new TsapPair(new Tsap(1, 2), new Tsap(3, 4)));
+            await conn.OpenAsync();
+            await conn.WriteClockAsync(new DateTime(2014, 08, 20, 11, 59, 43, 912));
+
+            conn.Close();
+        }
+
+        await Task.WhenAll(cs.Serve(out var port), Client(port));
+    }
+}

S7.Net.UnitTest/CommunicationTests/ConnectionOpen.cs

@@ -0,0 +1,28 @@
+using System.Net;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using S7.Net.Protocol;
+
+namespace S7.Net.UnitTest.CommunicationTests;
+
+[TestClass]
+public class ConnectionOpen
+{
+    [TestMethod]
+    public async Task Does_Not_Throw()
+    {
+        var cs = new CommunicationSequence {
+            ConnectionOpenTemplates.ConnectionRequestConfirm,
+            ConnectionOpenTemplates.CommunicationSetup
+        };
+
+        async Task Client(int port)
+        {
+            var conn = new Plc(IPAddress.Loopback.ToString(), port, new TsapPair(new Tsap(1, 2), new Tsap(3, 4)));
+            await conn.OpenAsync();
+            conn.Close();
+        }
+
+        await Task.WhenAll(cs.Serve(out var port), Client(port));
+    }
+}

S7.Net.UnitTest/CommunicationTests/ConnectionOpenTemplates.cs

@@ -0,0 +1,107 @@
+namespace S7.Net.UnitTest.CommunicationTests;
+
+internal static class ConnectionOpenTemplates
+{
+    public static RequestResponsePair ConnectionRequestConfirm { get; } = new RequestResponsePair(
+        """
+            // TPKT
+            03 // Version
+            00 // Reserved
+            00 16 // Length
+
+            // CR
+            11 // Number of bytes following
+            E0 // CR / Credit
+            00 00 // Destination reference, unused
+            __ __ // Source reference, unused
+            00 // Class / Option
+
+            // Source TSAP
+            C1 // Parameter code
+            02 // Parameter length
+            TSAP_SRC_CHAN // Channel
+            TSAP_SRC_POS // Position
+
+            // Destination TSAP
+            C2 // Parameter code
+            02 // Parameter length
+            TSAP_DEST_CHAN // Channel
+            TSAP_DEST_POS // Position
+
+            // PDU Size parameter
+            C0 // Parameter code
+            01 // Parameter length
+            0A // 1024 byte PDU (2 ^ 10)
+        """,
+        """
+            // TPKT
+            03 // Version
+            00 // Reserved
+            00 0B // Length
+
+            // CC
+            06 // Length
+            D0 // CC / Credit
+            00 00 // Destination reference
+            00 00 // Source reference
+            00 // Class / Option
+        """
+    );
+
+    public static RequestResponsePair CommunicationSetup { get; } = new RequestResponsePair(
+        """
+            // TPKT
+            03 // Version
+            00 // Reserved
+            00 19 // Length
+
+            // Data header
+            02 // Length
+            F0 // Data identifier
+            80 // PDU number and end of transmission
+
+            // S7 header
+            32 // Protocol ID
+            01 // Message type job request
+            00 00 // Reserved
+            PDU1 PDU2 // PDU reference
+            00 08 // Parameter length (Communication Setup)
+            00 00 // Data length
+
+            // Communication Setup
+            F0 // Function code
+            00 // Reserved
+            00 03 // Max AMQ caller
+            00 03 // Max AMQ callee
+            03 C0 // PDU size (960)
+        """,
+        """
+            // TPKT
+            03 // Version
+            00 // Reserved
+            00 1B // Length
+
+            // Data header
+            02 // Length
+            F0 // Data identifier
+            80 // PDU number and end of transmission
+
+            // S7 header
+            32 // Protocol ID
+            03 // Message type ack data
+            00 00 // Reserved
+            PDU1 PDU2 // PDU reference
+            00 08 // Parameter length (Communication Setup)
+            00 00 // Data length
+            00 // Error class
+            00 // Error code
+
+            // Communication Setup
+            F0 // Function code
+            00 // Reserved
+            00 03 // Max AMQ caller
+            00 03 // Max AMQ callee
+            03 C0 // PDU size (960)
+        """
+    );
+}

S7.Net.UnitTest/CommunicationTests/ReadPlcStatus.cs

@@ -0,0 +1,57 @@
+using System.Net;
+using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using S7.Net.Protocol;
+
+namespace S7.Net.UnitTest.CommunicationTests;
+
+[TestClass]
+public class ReadPlcStatus
+{
+    [TestMethod]
+    public async Task Read_Status_Run()
+    {
+        var cs = new CommunicationSequence {
+            ConnectionOpenTemplates.ConnectionRequestConfirm,
+            ConnectionOpenTemplates.CommunicationSetup,
+            {
+                """
+                    // TPKT
+                    03 00 00 21
+
+                    // COTP
+                    02 f0 80
+
+                    // S7 SZL read
+                    32 07 00 00 PDU1 PDU2 00 08 00 08 00 01 12 04 11 44
+                    01 00 ff 09 00 04 04 24 00 00
+                """,
+                """
+                    // TPKT
+                    03 00 00 3d
+
+                    // COTP
+                    02 f0 80
+
+                    // S7 SZL response
+                    32 07 00 00 PDU1 PDU2 00 0c 00 20 00 01 12 08 12 84
+                    01 02 00 00 00 00 ff 09 00 1c 04 24 00 00 00 14
+                    00 01 51 44 ff 08 00 00 00 00 00 00 00 00 14 08
+                    20 12 05 28 34 94
+                """
+            }
+        };
+
+        async Task Client(int port)
+        {
+            var conn = new Plc(IPAddress.Loopback.ToString(), port, new TsapPair(new Tsap(1, 2), new Tsap(3, 4)));
+            await conn.OpenAsync();
+            var status = await conn.ReadStatusAsync();
+
+            Assert.AreEqual(0x08, status);
+            conn.Close();
+        }
+
+        await Task.WhenAll(cs.Serve(out var port), Client(port));
+    }
+}

S7.Net.UnitTest/ConnectionCloseTest.cs

@@ -0,0 +1,181 @@
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.IO;
+using System.Linq;
+using System.Net.Sockets;
+using System.Reflection;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace S7.Net.UnitTest
+{
+    /// <summary>
+    /// Test stream which only gives 1 byte per read.
+    /// </summary>
+    class TestStreamConnectionClose : Stream
+    {
+        private readonly CancellationTokenSource _cancellationTokenSource;
+
+        public TestStreamConnectionClose(CancellationTokenSource cancellationTokenSource)
+        {
+            _cancellationTokenSource = cancellationTokenSource;
+        }
+        public override bool CanRead => false;
+
+        public override bool CanSeek => throw new NotImplementedException();
+
+        public override bool CanWrite => true;
+
+        public override long Length => throw new NotImplementedException();
+
+        public override long Position { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
+
+        public override void Flush()
+        {
+            throw new NotImplementedException();
+        }
+        
+        public override int Read(byte[] buffer, int offset, int count)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override long Seek(long offset, SeekOrigin origin)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override void SetLength(long value)
+        {
+            throw new NotImplementedException();
+        }
+
+        public override void Write(byte[] buffer, int offset, int count)
+        {
+            _cancellationTokenSource.Cancel();
+        }
+    }
+
+    /// <summary>
+    /// These tests are intended to test <see cref="StreamExtensions"/> functions and other stream-related special cases.
+    /// </summary>
+    [TestClass]
+    public class ConnectionCloseTest
+    {
+        const short TestServerPort = 31122;
+        const string TestServerIp = "127.0.0.1";
+
+        [TestMethod]
+        public async Task Test_CancellationDuringTransmission()
+        {
+            var plc = new Plc(CpuType.S7300, TestServerIp, TestServerPort, 0, 2);
+
+            // Set up a shared cancellation source so we can let the stream
+            // initiate cancel after some data has been written to it.
+            var cancellationSource = new CancellationTokenSource();
+            var cancellationToken = cancellationSource.Token;
+
+            var stream = new TestStreamConnectionClose(cancellationSource);
+            var requestData = new byte[100]; // empty data, it does not matter what is in there
+
+            // Set up access to private method and field
+            var dynMethod = plc.GetType().GetMethod("NoLockRequestTpduAsync",
+                BindingFlags.NonPublic | BindingFlags.Instance);
+            if (dynMethod == null)
+            {
+                throw new NullReferenceException("Could not find method 'NoLockRequestTpduAsync' on Plc object.");
+            }
+            var tcpClientField = plc.GetType().GetField("tcpClient", BindingFlags.NonPublic | BindingFlags.Instance);
+            if (tcpClientField == null)
+            {
+                throw new NullReferenceException("Could not find field 'tcpClient' on Plc object.");
+            }
+
+            // Set a value to tcpClient field so we can later ensure that it has been closed.
+            tcpClientField.SetValue(plc, new TcpClient());
+            var tcpClientValue = tcpClientField.GetValue(plc);
+            Assert.IsNotNull(tcpClientValue);
+            
+            try
+            {
+                var result = (Task<COTP.TPDU>) dynMethod.Invoke(plc, new object[] { stream, requestData, cancellationToken });
+                await result;
+            }
+            catch (OperationCanceledException)
+            {
+                Console.WriteLine("Task was cancelled as expected.");
+
+                // Ensure that the plc connection was closed since the task was cancelled
+                // after data has been sent through the network. We expect that the tcpClient
+                // object was set to NULL
+                var tcpClientValueAfter = tcpClientField.GetValue(plc);
+                Assert.IsNull(tcpClientValueAfter);
+                return;
+            }
+            catch (Exception e)
+            {
+                Assert.Fail($"Wrong exception type received. Expected {typeof(OperationCanceledException)}, received {e.GetType()}.");
+            }
+
+            // Ensure test fails if cancellation did not occur.
+            Assert.Fail("Task was not cancelled as expected.");
+        }
+
+        [TestMethod]
+        public async Task Test_CancellationBeforeTransmission()
+        {
+            var plc = new Plc(CpuType.S7300, TestServerIp, TestServerPort, 0, 2);
+
+            // Set up a cancellation source
+            var cancellationSource = new CancellationTokenSource();
+            var cancellationToken = cancellationSource.Token;
+
+            var stream = new TestStreamConnectionClose(cancellationSource);
+            var requestData = new byte[100]; // empty data, it does not matter what is in there
+
+            // Set up access to private method and field
+            var dynMethod = plc.GetType().GetMethod("NoLockRequestTpduAsync",
+                BindingFlags.NonPublic | BindingFlags.Instance);
+            if (dynMethod == null)
+            {
+                throw new NullReferenceException("Could not find method 'NoLockRequestTpduAsync' on Plc object.");
+            }
+            var tcpClientField = plc.GetType().GetField("tcpClient", BindingFlags.NonPublic | BindingFlags.Instance);
+            if (tcpClientField == null)
+            {
+                throw new NullReferenceException("Could not find field 'tcpClient' on Plc object.");
+            }
+
+            // Set a value to tcpClient field so we can later ensure that it has been closed.
+            tcpClientField.SetValue(plc, new TcpClient());
+            var tcpClientValue = tcpClientField.GetValue(plc);
+            Assert.IsNotNull(tcpClientValue);
+
+            try
+            {
+                // cancel the task before we start transmitting data
+                cancellationSource.Cancel();
+                var result = (Task<COTP.TPDU>)dynMethod.Invoke(plc, new object[] { stream, requestData, cancellationToken });
+                await result;
+            }
+            catch (OperationCanceledException)
+            {
+                Console.WriteLine("Task was cancelled as expected.");
+
+                // Ensure that the plc connection was not closed, since we cancelled the task before
+                // sending data through the network. We expect that the tcpClient
+                // object was NOT set to NULL
+                var tcpClientValueAfter = tcpClientField.GetValue(plc);
+                Assert.IsNotNull(tcpClientValueAfter);
+                return;
+            }
+            catch (Exception e)
+            {
+                Assert.Fail($"Wrong exception type received. Expected {typeof(OperationCanceledException)}, received {e.GetType()}.");
+            }
+
+            // Ensure test fails if cancellation did not occur.
+            Assert.Fail("Task was not cancelled as expected.");
+        }
+    }
+}

S7.Net.UnitTest/ConnectionRequestTest.cs

@@ -9,52 +9,52 @@ namespace S7.Net.UnitTest
         [TestMethod]
         public void Test_ConnectionRequest_S7_200()
         {
-            CollectionAssert.AreEqual(MakeConnectionRequest(16, 0, 16, 0),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S7200, 0, 0));
+            CollectionAssert.AreEqual(MakeConnectionRequest(16, 0, 16, 1),
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S7200, 0, 0)));
         }
 
         [TestMethod]
         public void Test_ConnectionRequest_S7_300()
         {
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 0),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S7300, 0, 0));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S7300, 0, 0)));
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 1),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S7300, 0, 1));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S7300, 0, 1)));
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 33),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S7300, 1, 1));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S7300, 1, 1)));
         }
 
         [TestMethod]
         public void Test_ConnectionRequest_S7_400()
         {
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 0),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S7400, 0, 0));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S7400, 0, 0)));
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 1),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S7400, 0, 1));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S7400, 0, 1)));
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 33),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S7400, 1, 1));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S7400, 1, 1)));
         }
 
         [TestMethod]
         public void Test_ConnectionRequest_S7_1200()
         {
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 0),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S71200, 0, 0));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S71200, 0, 0)));
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 1),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S71200, 0, 1));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S71200, 0, 1)));
             CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 33),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S71200, 1, 1));
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S71200, 1, 1)));
         }
 
         [TestMethod]
         public void Test_ConnectionRequest_S7_1500()
         {
-            CollectionAssert.AreEqual(MakeConnectionRequest(0x10, 0x2, 3, 0),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S71500, 0, 0));
-            CollectionAssert.AreEqual(MakeConnectionRequest(0x10, 0x2, 3, 1),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S71500, 0, 1));
-            CollectionAssert.AreEqual(MakeConnectionRequest(0x10, 0x2, 3, 33),
-                ConnectionRequest.GetCOTPConnectionRequest(CpuType.S71500, 1, 1));
+            CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 0),
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S71500, 0, 0)));
+            CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 1),
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S71500, 0, 1)));
+            CollectionAssert.AreEqual(MakeConnectionRequest(1, 0, 3, 33),
+                ConnectionRequest.GetCOTPConnectionRequest(TsapPair.GetDefaultTsapPair(CpuType.S71500, 1, 1)));
         }
 
         private static byte[] MakeConnectionRequest(byte sourceTsap1, byte sourceTsap2, byte destTsap1, byte destTsap2)
@@ -63,7 +63,7 @@ namespace S7.Net.UnitTest
             {
                 3, 0, 0, 22, //TPKT
                 17, //COTP Header Length
-                224, //Connect Request 
+                224, //Connect Request
                 0, 0, //Destination Reference
                 0, 46, //Source Reference
                 0, //Flags

S7.Net.UnitTest/ConvertersUnitTest.cs

@@ -24,5 +24,21 @@ namespace S7.Net.UnitTest
             Assert.IsFalse(dummyByte.SelectBit(7));
 
         }
+
+        [TestMethod]
+        public void T01_TestSetBit()
+        {
+            byte dummyByte = 0xAA; // 1010 1010
+            dummyByte.SetBit(0, true);
+            dummyByte.SetBit(1, false);
+            dummyByte.SetBit(2, true);
+            dummyByte.SetBit(3, false);
+            Assert.AreEqual<byte>(dummyByte, 0xA5);// 1010 0101
+            dummyByte.SetBit(4, true);
+            dummyByte.SetBit(5, true);
+            dummyByte.SetBit(6, true);
+            dummyByte.SetBit(7, true);
+            Assert.AreEqual<byte>(dummyByte, 0xF5);// 1111 0101
+        }
     }
 }

S7.Net.UnitTest/Framework/IsExternalInit.cs

@@ -0,0 +1,7 @@
+using System.ComponentModel;
+
+namespace System.Runtime.CompilerServices
+{
+    [EditorBrowsable(EditorBrowsableState.Never)]
+    internal record IsExternalInit;
+}

S7.Net.UnitTest/Helpers/TestClass.cs

@@ -1,4 +1,6 @@
 
+using S7.Net.Types;
+
 namespace S7.Net.UnitTest.Helpers
 {
     class TestClass
@@ -51,5 +53,16 @@ namespace S7.Net.UnitTest.Helpers
         /// DB1.DBD16
         /// </summary>
         public ushort DWordVariable { get; set; }
+
+        /// <summary>
+        /// DB1.DBX20.0
+        /// </summary>
+        [S7String(S7StringType.S7WString, 10)]
+        public string WStringVariable { get; set; }
+        /// <summary>
+        /// DB1.DBX44.0
+        /// </summary>
+        [S7String(S7StringType.S7String, 10)]
+        public string StringVariable { get; set; }
     }
 }

S7.Net.UnitTest/Infrastructure/CommunicationSequence.cs

@@ -0,0 +1,82 @@
+using System;
+using System.Buffers;
+using System.Collections;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net;
+using System.Net.Sockets;
+using System.Threading.Tasks;
+
+namespace S7.Net.UnitTest;
+
+internal class CommunicationSequence : IEnumerable<RequestResponsePair>
+{
+    private readonly List<RequestResponsePair> _requestResponsePairs = new List<RequestResponsePair>();
+
+    public void Add(RequestResponsePair requestResponsePair)
+    {
+        _requestResponsePairs.Add(requestResponsePair);
+    }
+
+    public void Add(string requestPattern, string responsePattern)
+    {
+        _requestResponsePairs.Add(new RequestResponsePair(requestPattern, responsePattern));
+    }
+
+    public IEnumerator<RequestResponsePair> GetEnumerator()
+    {
+        return _requestResponsePairs.GetEnumerator();
+    }
+
+    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+
+    public Task Serve(out int port)
+    {
+        var socket = CreateBoundListenSocket(out port);
+        socket.Listen(0);
+
+        async Task Impl()
+        {
+            await Task.Yield();
+            var socketIn = socket.Accept();
+
+            var buffer = ArrayPool<byte>.Shared.Rent(1024);
+            try
+            {
+                foreach (var pair in _requestResponsePairs)
+                {
+                    var bytesReceived = socketIn.Receive(buffer, SocketFlags.None);
+
+                    var received = buffer.Take(bytesReceived).ToArray();
+                    Console.WriteLine($"=> {BitConverter.ToString(received)}");
+
+                    var response = Responder.Respond(pair, received);
+
+                    Console.WriteLine($"<= {BitConverter.ToString(response)}");
+                    socketIn.Send(response);
+                }
+            }
+            finally
+            {
+                ArrayPool<byte>.Shared.Return(buffer);
+            }
+
+            socketIn.Close();
+        }
+
+        return Impl();
+    }
+
+    private static Socket CreateBoundListenSocket(out int port)
+    {
+        var socket = new Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp);
+        var endpoint = new IPEndPoint(IPAddress.Loopback, 0);
+
+        socket.Bind(endpoint);
+
+        var localEndpoint = (IPEndPoint)socket.LocalEndPoint!;
+        port = localEndpoint.Port;
+
+        return socket;
+    }
+}

S7.Net.UnitTest/Infrastructure/RequestResponsePair.cs

@@ -0,0 +1,3 @@
+namespace S7.Net.UnitTest;
+
+internal record RequestResponsePair(string RequestPattern, string ResponsePattern);

S7.Net.UnitTest/Infrastructure/Responder.cs

@@ -0,0 +1,80 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.IO;
+
+namespace S7.Net.UnitTest;
+
+internal static class Responder
+{
+    private const string Comment = "//";
+    private static char[] Space = " ".ToCharArray();
+
+    public static byte[] Respond(RequestResponsePair pair, byte[] request)
+    {
+        var offset = 0;
+        var matches = new Dictionary<string, byte>();
+        var res = new List<byte>();
+        using var requestReader = new StringReader(pair.RequestPattern);
+
+        string line;
+        while ((line = requestReader.ReadLine()) != null)
+        {
+            var tokens = line.Split(Space, StringSplitOptions.RemoveEmptyEntries);
+            foreach (var token in tokens)
+            {
+                if (token.StartsWith(Comment)) break;
+
+                if (offset >= request.Length)
+                {
+                    throw new Exception("Request pattern has more data than request.");
+                }
+
+                var received = request[offset];
+
+                if (token.Length == 2 && byte.TryParse(token, NumberStyles.HexNumber, CultureInfo.InvariantCulture, out var value))
+                {
+                    // Number, exact match
+                    if (value != received)
+                    {
+                        throw new Exception($"Incorrect data at offset {offset}. Expected {value:X2}, received {received:X2}.");
+                    }
+                }
+                else
+                {
+                    matches[token] = received;
+                }
+
+                offset++;
+            }
+        }
+
+        if (offset != request.Length) throw new Exception("Request contained more data than request pattern.");
+
+        using var responseReader = new StringReader(pair.ResponsePattern);
+        while ((line = responseReader.ReadLine()) != null)
+        {
+            var tokens = line.Split(Space, StringSplitOptions.RemoveEmptyEntries);
+            foreach (var token in tokens)
+            {
+                if (token.StartsWith(Comment)) break;
+
+                if (token.Length == 2 && byte.TryParse(token, NumberStyles.HexNumber, CultureInfo.InvariantCulture, out var value))
+                {
+                    res.Add(value);
+                }
+                else
+                {
+                    if (!matches.TryGetValue(token, out var match))
+                    {
+                        throw new Exception($"Unmatched token '{token}' in response.");
+                    }
+
+                    res.Add(match);
+                }
+            }
+        }
+
+        return res.ToArray();
+    }
+}

S7.Net.UnitTest/ProtocolTests.cs

@@ -1,14 +1,10 @@
 using System;
-using System.Collections.Generic;
-using System.Linq;
-using System.Text;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
-using S7.Net;
-
 using System.IO;
+using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
 using S7.Net.Protocol;
-using System.Collections;
 
 namespace S7.Net.UnitTest
 {
@@ -21,21 +17,17 @@ namespace S7.Net.UnitTest
         public async Task TPKT_Read()
         {
             var m = new MemoryStream(StringToByteArray("0300002902f0803203000000010002001400000401ff0400807710000100000103000000033f8ccccd"));
-            var t = TPKT.Read(m);
-            Assert.AreEqual(0x03, t.Version);
-            Assert.AreEqual(0x29, t.Length);
-            m.Position = 0;
-            t = await TPKT.ReadAsync(m, TestContext.CancellationTokenSource.Token);
+            var t = await TPKT.ReadAsync(m, TestContext.CancellationTokenSource.Token);
             Assert.AreEqual(0x03, t.Version);
             Assert.AreEqual(0x29, t.Length);
         }
 
         [TestMethod]
         [ExpectedException(typeof(TPKTInvalidException))]
-        public void TPKT_ReadShort()
+        public async Task TPKT_ReadShort()
         {
             var m = new MemoryStream(StringToByteArray("0300002902f0803203000000010002001400000401ff040080"));
-            var t = TPKT.Read(m);
+            var t = await TPKT.ReadAsync(m, CancellationToken.None);
         }
 
 
@@ -48,14 +40,11 @@ namespace S7.Net.UnitTest
         }
 
         [TestMethod]
-        public void COTP_ReadTSDU()
+        public async Task COTP_ReadTSDU()
         {
             var expected = StringToByteArray("320700000400000800080001120411440100ff09000400000000");
             var m = new MemoryStream(StringToByteArray("0300000702f0000300000702f0000300002102f080320700000400000800080001120411440100ff09000400000000"));
-            var t = COTP.TSDU.Read(m);
-            Assert.IsTrue(expected.SequenceEqual(t));
-            m.Position = 0;
-            t = COTP.TSDU.ReadAsync(m, TestContext.CancellationTokenSource.Token).Result;
+            var t = await COTP.TSDU.ReadAsync(m, TestContext.CancellationTokenSource.Token);
             Assert.IsTrue(expected.SequenceEqual(t));
         }
 
@@ -69,14 +58,13 @@ namespace S7.Net.UnitTest
 
 
         [TestMethod]
-        public void TestResponseCode()
+        public async Task TestResponseCode()
         {
             var expected = StringToByteArray("320700000400000800080001120411440100ff09000400000000");
             var m = new MemoryStream(StringToByteArray("0300000702f0000300000702f0000300002102f080320700000400000800080001120411440100ff09000400000000"));
-            var t = COTP.TSDU.Read(m);
+            var t = await COTP.TSDU.ReadAsync(m, CancellationToken.None);
             Assert.IsTrue(expected.SequenceEqual(t));
 
-
             // Test all possible byte values. Everything except 0xff should throw an exception.
             var testData = Enumerable.Range(0, 256).Select(i => new { StatusCode = (ReadWriteErrorCode)i, ThrowsException = i != (byte)ReadWriteErrorCode.Success });
 

S7.Net.UnitTest/S7.Net.UnitTest.csproj

@@ -1,8 +1,14 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
-  <PropertyGroup>
-    <TargetFrameworks>net452;netcoreapp3.1</TargetFrameworks>
+  <PropertyGroup Condition=" '$(OS)' != 'Windows_NT' ">
+    <TargetFrameworks>net6.0;net7.0</TargetFrameworks>
+  </PropertyGroup>
+  <PropertyGroup Condition=" '$(OS)' == 'Windows_NT' "> 
+    <TargetFrameworks>net6.0;net7.0;net462</TargetFrameworks>
+  </PropertyGroup>
 
+  <PropertyGroup>
+    <LangVersion>latest</LangVersion>
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>Properties\S7.Net.snk</AssemblyOriginatorKeyFile>
     <IsPackable>false</IsPackable>
@@ -11,7 +17,10 @@
   </PropertyGroup>
   
   <ItemGroup>
-    <PackageReference Include="GitHubActionsTestLogger" Version="1.1.0" />
+    <PackageReference Include="GitHubActionsTestLogger" Version="2.3.2">
+      <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+      <PrivateAssets>all</PrivateAssets>
+    </PackageReference>
     <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.7.0" />
     <PackageReference Include="MSTest.TestAdapter" Version="2.1.2" />
     <PackageReference Include="MSTest.TestFramework" Version="2.1.2" />

S7.Net.UnitTest/S7NetTestsAsync.cs

@@ -7,6 +7,12 @@ using S7.Net.Types;
 using S7.UnitTest.Helpers;
 using System.Threading.Tasks;
 using System.Threading;
+using System.Security.Cryptography;
+
+
+#if NET5_0_OR_GREATER
+using System.Buffers;
+#endif
 
 #endregion
 
@@ -138,6 +144,33 @@ namespace S7.Net.UnitTest
             CollectionAssert.AreEqual(data, readData);
         }
 
+#if NET5_0_OR_GREATER
+
+        /// <summary>
+        /// Write/Read a large amount of data to test PDU max
+        /// </summary>
+        [TestMethod]
+        public async Task Test_Async_WriteLargeByteArrayWithMemory()
+        {
+            Assert.IsTrue(plc.IsConnected, "Before executing this test, the plc must be connected. Check constructor.");
+
+            var randomEngine = new Random();
+            using var dataOwner = MemoryPool<byte>.Shared.Rent(8192);
+            var data = dataOwner.Memory.Slice(0, 8192);
+            var db = 2;
+            randomEngine.NextBytes(data.Span);
+
+            await plc.WriteBytesAsync(DataType.DataBlock, db, 0, data);
+
+            using var readDataOwner = MemoryPool<byte>.Shared.Rent(data.Length);
+            var readData = readDataOwner.Memory.Slice(0, data.Length);
+            await plc.ReadBytesAsync(readData, DataType.DataBlock, db, 0);
+
+            CollectionAssert.AreEqual(data.ToArray(), readData.ToArray());
+        }
+
+#endif
+
         /// <summary>
         /// Read/Write a class that has the same properties of a DB with the same field in the same order
         /// </summary>
@@ -154,7 +187,9 @@ namespace S7.Net.UnitTest
                 IntVariable = -15000,
                 LRealVariable = -154.789,
                 RealVariable = -154.789f,
-                DWordVariable = 850
+                DWordVariable = 850,
+                WStringVariable = "ÄÜÉÊéà",
+                StringVariable = "Hallo"
             };
 
             await plc.WriteClassAsync(tc, DB2);
@@ -168,6 +203,8 @@ namespace S7.Net.UnitTest
             Assert.AreEqual(tc.LRealVariable, tc2.LRealVariable);
             Assert.AreEqual(tc.RealVariable, tc2.RealVariable);
             Assert.AreEqual(tc.DWordVariable, tc2.DWordVariable);
+            Assert.AreEqual(tc.WStringVariable, tc2.WStringVariable);
+            Assert.AreEqual(tc.StringVariable, tc2.StringVariable);
         }
 
         [TestMethod]
@@ -580,7 +617,9 @@ namespace S7.Net.UnitTest
                 IntVariable = -15000,
                 LRealVariable = -154.789,
                 RealVariable = -154.789f,
-                DWordVariable = 850
+                DWordVariable = 850,
+                WStringVariable = "ÄÜÉÊéà",
+                StringVariable = "Hallo"
             };
 
             await plc.WriteClassAsync(tc, DB2);
@@ -628,7 +667,10 @@ namespace S7.Net.UnitTest
                 IntVariable = -15000,
                 LRealVariable = -154.789,
                 RealVariable = -154.789f,
-                DWordVariable = 850
+                DWordVariable = 850,
+                WStringVariable = "ÄÜÉÊéà",
+                StringVariable = "Hallo"
+
             };
 
             await plc.WriteClassAsync(tc, DB2);
@@ -646,6 +688,9 @@ namespace S7.Net.UnitTest
             Assert.AreEqual(Math.Round(tc2.LRealVariable, 3), Math.Round(tc2Generic.LRealVariable, 3));
             Assert.AreEqual(tc2.RealVariable, tc2Generic.RealVariable);
             Assert.AreEqual(tc2.DWordVariable, tc2Generic.DWordVariable);
+            Assert.AreEqual(tc2.WStringVariable, tc2Generic.WStringVariable);
+            Assert.AreEqual(tc2.StringVariable, tc2Generic.StringVariable);
+
         }
 
         [TestMethod]
@@ -671,7 +716,9 @@ namespace S7.Net.UnitTest
                 IntVariable = -15000,
                 LRealVariable = -154.789,
                 RealVariable = -154.789f,
-                DWordVariable = 850
+                DWordVariable = 850,
+                WStringVariable = "ÄÜÉÊéà",
+                StringVariable = "Hallo"
             };
 
             await plc.WriteClassAsync(tc, DB2);
@@ -686,6 +733,8 @@ namespace S7.Net.UnitTest
             Assert.AreEqual(Math.Round(tc2Generic.LRealVariable, 3), Math.Round(tc2GenericWithClassFactory.LRealVariable, 3));
             Assert.AreEqual(tc2Generic.RealVariable, tc2GenericWithClassFactory.RealVariable);
             Assert.AreEqual(tc2Generic.DWordVariable, tc2GenericWithClassFactory.DWordVariable);
+            Assert.AreEqual(tc2Generic.WStringVariable, tc2GenericWithClassFactory.WStringVariable);
+            Assert.AreEqual(tc2Generic.StringVariable, tc2GenericWithClassFactory.StringVariable);
         }
 
         [TestMethod]
@@ -792,7 +841,9 @@ namespace S7.Net.UnitTest
                 IntVariable = -15000,
                 LRealVariable = -154.789,
                 RealVariable = -154.789f,
-                DWordVariable = 850
+                DWordVariable = 850,
+                WStringVariable = "ÄÜÉÊéà",
+                StringVariable = "Hallo"
             };
             plc.WriteClass(tc, DB2);
 
@@ -914,6 +965,31 @@ namespace S7.Net.UnitTest
             }
         }
 
+#if NET5_0_OR_GREATER
+
+        [TestMethod]
+        public async Task Test_Async_ReadWriteBytesManyWithMemory()
+        {
+            Assert.IsTrue(plc.IsConnected, "Before executing this test, the plc must be connected. Check constructor.");
+
+            using var data = MemoryPool<byte>.Shared.Rent(2000);
+            for (int i = 0; i < data.Memory.Length; i++)
+                data.Memory.Span[i] = (byte)(i % 256);
+
+            await plc.WriteBytesAsync(DataType.DataBlock, 2, 0, data.Memory);
+
+            using var readData = MemoryPool<byte>.Shared.Rent(data.Memory.Length);
+
+            await plc.ReadBytesAsync(readData.Memory.Slice(0, data.Memory.Length), DataType.DataBlock, 2, 0);
+
+            for (int x = 0; x < data.Memory.Length; x++)
+            {
+                Assert.AreEqual(x % 256, readData.Memory.Span[x], string.Format("Bit {0} failed", x));
+            }
+        }
+
+#endif
+
         /// <summary>
         /// Write a large amount of data and test cancellation
         /// </summary>
@@ -930,25 +1006,100 @@ namespace S7.Net.UnitTest
             var db = 2;
             randomEngine.NextBytes(data);
 
-            cancellationSource.CancelAfter(TimeSpan.FromMilliseconds(5));
+            cancellationSource.CancelAfter(System.TimeSpan.FromMilliseconds(5));
             try
             {
                 await plc.WriteBytesAsync(DataType.DataBlock, db, 0, data, cancellationToken);
             }
-            catch(TaskCanceledException)
+            catch(OperationCanceledException)
             {
                 // everything is good, that is the exception we expect
-                Console.WriteLine("Task was cancelled as expected.");
+                Console.WriteLine("Operation was cancelled as expected.");
                 return;
             }
             catch(Exception e)
             {
-                Assert.Fail($"Wrong exception type received. Expected {typeof(TaskCanceledException)}, received {e.GetType()}.");
+                Assert.Fail($"Wrong exception type received. Expected {typeof(OperationCanceledException)}, received {e.GetType()}.");
             }
 
             // Depending on how tests run, this can also just succeed without getting cancelled at all. Do nothing in this case.
             Console.WriteLine("Task was not cancelled as expected.");
         }
+
+#if NET5_0_OR_GREATER
+
+        /// <summary>
+        /// Write a large amount of data and test cancellation
+        /// </summary>
+        [TestMethod]
+        public async Task Test_Async_WriteLargeByteArrayWithCancellationWithMemory()
+        {
+            Assert.IsTrue(plc.IsConnected, "Before executing this test, the plc must be connected. Check constructor.");
+
+            var cancellationSource = new CancellationTokenSource();
+            var cancellationToken = cancellationSource.Token;
+
+            using var dataOwner = MemoryPool<byte>.Shared.Rent(8192);
+            var data = dataOwner.Memory.Slice(0, 8192);
+            var randomEngine = new Random();
+            var db = 2;
+            randomEngine.NextBytes(data.Span);
+
+            cancellationSource.CancelAfter(System.TimeSpan.FromMilliseconds(5));
+            try
+            {
+                await plc.WriteBytesAsync(DataType.DataBlock, db, 0, data, cancellationToken);
+            }
+            catch (OperationCanceledException)
+            {
+                // everything is good, that is the exception we expect
+                Console.WriteLine("Operation was cancelled as expected.");
+                return;
+            }
+            catch (Exception e)
+            {
+                Assert.Fail($"Wrong exception type received. Expected {typeof(OperationCanceledException)}, received {e.GetType()}.");
+            }
+
+            // Depending on how tests run, this can also just succeed without getting cancelled at all. Do nothing in this case.
+            Console.WriteLine("Task was not cancelled as expected.");
+        }
+
+#endif
+
+        /// <summary>
+        /// Write a large amount of data and test cancellation
+        /// </summary>
+        [TestMethod]
+        public async Task Test_Async_ParseDataIntoDataItemsAlignment()
+        {
+            Assert.IsTrue(plc.IsConnected, "Before executing this test, the plc must be connected. Check constructor.");
+
+            var db = 2;
+            // First write a sensible S7 string capacity
+            await plc.WriteBytesAsync(DataType.DataBlock, db, 0, new byte[] {5, 0});
+
+            // Read two data items, with the first having odd number of bytes (7),
+            // and the second has to be aligned on a even address
+            var dataItems = new List<DataItem>
+            {
+                new DataItem
+                {
+                    DataType = DataType.DataBlock,
+                    DB = db,
+                    VarType = VarType.S7String,
+                    Count = 5
+                },
+                new DataItem
+                {
+                    DataType = DataType.DataBlock,
+                    DB = db,
+                    VarType = VarType.Word,
+                }
+            };
+            await plc.ReadMultipleVarsAsync(dataItems, CancellationToken.None);
+        }
+
         #endregion
     }
 }

S7.Net.UnitTest/S7NetTestsSync.cs

@@ -5,6 +5,11 @@ using Microsoft.VisualStudio.TestTools.UnitTesting;
 using S7.Net.UnitTest.Helpers;
 using S7.Net.Types;
 using S7.UnitTest.Helpers;
+using System.Security.Cryptography;
+
+#if NET5_0_OR_GREATER
+using System.Buffers;
+#endif
 
 #endregion
 
@@ -183,6 +188,9 @@ namespace S7.Net.UnitTest
             tc.LRealVariable = -154.789;
             tc.RealVariable = -154.789f;
             tc.DWordVariable = 850;
+            tc.WStringVariable = "ÄÜÉÊéà";
+            tc.StringVariable = "Hallo";
+
             plc.WriteClass(tc, DB2);
             TestClass tc2 = new TestClass();
             // Values that are read from a class are stored inside the class itself, that is passed by reference
@@ -194,6 +202,8 @@ namespace S7.Net.UnitTest
             Assert.AreEqual(tc.LRealVariable, tc2.LRealVariable);
             Assert.AreEqual(tc.RealVariable, tc2.RealVariable);
             Assert.AreEqual(tc.DWordVariable, tc2.DWordVariable);
+            Assert.AreEqual(tc.WStringVariable, tc2.WStringVariable);
+            Assert.AreEqual(tc.StringVariable, tc2.StringVariable);
         }
 
         /// <summary>
@@ -577,6 +587,8 @@ namespace S7.Net.UnitTest
             tc.LRealVariable = -154.789;
             tc.RealVariable = -154.789f;
             tc.DWordVariable = 850;
+            tc.WStringVariable = "ÄÜÉÊéà";
+            tc.StringVariable = "Hallo";
 
             plc.WriteClass(tc, DB2);
 
@@ -622,6 +634,8 @@ namespace S7.Net.UnitTest
             tc.LRealVariable = -154.789;
             tc.RealVariable = -154.789f;
             tc.DWordVariable = 850;
+            tc.WStringVariable = "ÄÜÉÊéà";
+            tc.StringVariable = "Hallo";
 
             plc.WriteClass(tc, DB2);
 
@@ -637,6 +651,8 @@ namespace S7.Net.UnitTest
             Assert.AreEqual(Math.Round(tc2.LRealVariable, 3), Math.Round(tc2Generic.LRealVariable, 3));
             Assert.AreEqual(tc2.RealVariable, tc2Generic.RealVariable);
             Assert.AreEqual(tc2.DWordVariable, tc2Generic.DWordVariable);
+            Assert.AreEqual(tc2.WStringVariable, tc2Generic.WStringVariable);
+            Assert.AreEqual(tc2.StringVariable, tc2Generic.StringVariable);
         }
 
         [TestMethod, ExpectedException(typeof(PlcException))]
@@ -665,6 +681,8 @@ namespace S7.Net.UnitTest
             tc.LRealVariable = -154.789;
             tc.RealVariable = -154.789f;
             tc.DWordVariable = 850;
+            tc.WStringVariable = "ÄÜÉÊéà";
+            tc.StringVariable = "Hallo";
 
             plc.WriteClass(tc, DB2);
 
@@ -679,6 +697,8 @@ namespace S7.Net.UnitTest
             Assert.AreEqual(Math.Round(tc2Generic.LRealVariable, 3), Math.Round(tc2GenericWithClassFactory.LRealVariable, 3));
             Assert.AreEqual(tc2Generic.RealVariable, tc2GenericWithClassFactory.RealVariable);
             Assert.AreEqual(tc2Generic.DWordVariable, tc2GenericWithClassFactory.DWordVariable);
+            Assert.AreEqual(tc2Generic.WStringVariable, tc2GenericWithClassFactory.WStringVariable);
+            Assert.AreEqual(tc2Generic.StringVariable, tc2GenericWithClassFactory.StringVariable);
         }
 
         [TestMethod, ExpectedException(typeof(PlcException))]
@@ -762,6 +782,33 @@ namespace S7.Net.UnitTest
             CollectionAssert.AreEqual(data, readData);
         }
 
+#if NET5_0_OR_GREATER
+
+        /// <summary>
+        /// Write/Read a large amount of data to test PDU max
+        /// </summary>
+        [TestMethod]
+        public void T33_WriteLargeByteArrayWithSpan()
+        {
+            Assert.IsTrue(plc.IsConnected, "Before executing this test, the plc must be connected. Check constructor.");
+
+            var randomEngine = new Random();
+            using var dataOwner = MemoryPool<byte>.Shared.Rent(8192);
+            var data = dataOwner.Memory.Span.Slice(0, 8192);
+            var db = 2;
+            randomEngine.NextBytes(data);
+
+            plc.WriteBytes(DataType.DataBlock, db, 0, data);
+
+            using var readDataOwner = MemoryPool<byte>.Shared.Rent(data.Length);
+            var readData = readDataOwner.Memory.Span.Slice(0, data.Length);
+            plc.ReadBytes(readData, DataType.DataBlock, db, 0);
+
+            CollectionAssert.AreEqual(data.ToArray(), readData.ToArray());
+        }
+
+#endif
+
         [TestMethod, ExpectedException(typeof(PlcException))]
         public void T18_ReadStructThrowsIfPlcIsNotConnected()
         {
@@ -837,6 +884,9 @@ namespace S7.Net.UnitTest
             tc.LRealVariable = -154.789;
             tc.RealVariable = -154.789f;
             tc.DWordVariable = 850;
+            tc.WStringVariable = "ÄÜÉÊéà";
+            tc.StringVariable = "Hallo";
+
             plc.WriteClass(tc, DB2);
 
             int expectedReadBytes = (int)Types.Class.GetClassSize(tc);
@@ -987,6 +1037,32 @@ namespace S7.Net.UnitTest
             }
         }
 
+#if NET5_0_OR_GREATER
+
+        [TestMethod]
+        public void T27_ReadWriteBytesManyWithSpan()
+        {
+            Assert.IsTrue(plc.IsConnected, "Before executing this test, the plc must be connected. Check constructor.");
+
+            using var dataOwner = MemoryPool<byte>.Shared.Rent(2000);
+            var data = dataOwner.Memory.Span;
+            for (int i = 0; i < data.Length; i++)
+                data[i] = (byte)(i % 256);
+
+            plc.WriteBytes(DataType.DataBlock, 2, 0, data);
+
+            using var readDataOwner = MemoryPool<byte>.Shared.Rent(data.Length);
+            var readData = readDataOwner.Memory.Span.Slice(0, data.Length);
+            plc.ReadBytes(readData, DataType.DataBlock, 2, 0);
+
+            for (int x = 0; x < data.Length; x++)
+            {
+                Assert.AreEqual(x % 256, readData[x], $"Mismatch at offset {x}, expected {x % 256}, actual {readData[x]}.");
+            }
+        }
+
+#endif
+
         [TestMethod]
         public void T28_ReadClass_DoesntCrash_When_ReadingLessThan1Byte()
         {
@@ -1041,7 +1117,7 @@ namespace S7.Net.UnitTest
             Assert.AreEqual(test_value, test_value2, "Compare DateTimeLong Write/Read");
         }
 
-        #endregion
+#endregion
 
         #region Private methods
 

S7.Net.UnitTest/StreamTests.cs

@@ -2,6 +2,7 @@
 using System;
 using System.IO;
 using System.Linq;
+using System.Threading;
 using System.Threading.Tasks;
 
 namespace S7.Net.UnitTest
@@ -15,6 +16,7 @@ namespace S7.Net.UnitTest
         {
             Data = data;
         }
+
         public override bool CanRead => _position < Data.Length;
 
         public override bool CanSeek => throw new NotImplementedException();
@@ -26,21 +28,31 @@ namespace S7.Net.UnitTest
         public override long Position { get => throw new NotImplementedException(); set => throw new NotImplementedException(); }
         public byte[] Data { get; }
 
+        int _position = 0;
+
         public override void Flush()
         {
             throw new NotImplementedException();
         }
 
-        int _position = 0;
         public override int Read(byte[] buffer, int offset, int count)
         {
+            throw new NotImplementedException();
+        }
+
+        public override Task<int> ReadAsync(byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+
             if (_position >= Data.Length)
             {
-                return 0;
+                return Task.FromResult(0);
             }
+
             buffer[offset] = Data[_position];
             ++_position;
-            return 1;
+
+            return Task.FromResult(1);
         }
 
         public override long Seek(long offset, SeekOrigin origin)
@@ -78,21 +90,21 @@ namespace S7.Net.UnitTest
         }
 
         [TestMethod]
-        public void TPKT_ReadRestrictedStream()
+        public async Task TPKT_ReadRestrictedStream()
         {
             var fullMessage = ProtocolUnitTest.StringToByteArray("0300002902f0803203000000010002001400000401ff0400807710000100000103000000033f8ccccd");
             var m = new TestStream1BytePerRead(fullMessage);
-            var t = TPKT.Read(m);
+            var t = await TPKT.ReadAsync(m, CancellationToken.None);
             Assert.AreEqual(fullMessage.Length, t.Length);
             Assert.AreEqual(fullMessage.Last(), t.Data.Last());
         }
 
         [TestMethod]
-        public void TPKT_ReadStreamTooShort()
+        public async Task TPKT_ReadStreamTooShort()
         {
             var fullMessage = ProtocolUnitTest.StringToByteArray("0300002902f0803203000000010002001400");
             var m = new TestStream1BytePerRead(fullMessage);
-            Assert.ThrowsException<TPKTInvalidException>(() => TPKT.Read(m));
+            await Assert.ThrowsExceptionAsync<TPKTInvalidException>(() => TPKT.ReadAsync(m, CancellationToken.None));
         }
     }
 }

S7.Net.UnitTest/TypeTests/ClassTests.cs

@@ -17,6 +17,19 @@ namespace S7.Net.UnitTest.TypeTests
             Assert.AreEqual(Class.GetClassSize(new TestClassUnevenSize(3, 17)), 10);
         }
 
+        /// <summary>
+        /// Ensure Uint32 is correctly parsed through ReadClass functions. Adresses issue https://github.com/S7NetPlus/s7netplus/issues/414
+        /// </summary>
+        [TestMethod]
+        public void TestUint32Read()
+        {
+            var result = new TestUint32();
+            var data = new byte[4] { 0, 0, 0, 5 };
+            var bytesRead = Class.FromBytes(result, data);
+            Assert.AreEqual(bytesRead, data.Length);
+            Assert.AreEqual(5u, result.Value1);
+        }
+
         private class TestClassUnevenSize
         {
             public bool Bool { get; set; }
@@ -29,5 +42,10 @@ namespace S7.Net.UnitTest.TypeTests
                 Bools = new bool[bitCount];
             }
         }
+
+        private class TestUint32
+        {
+            public uint Value1 { get; set; }
+        }
     }
 }

S7.Net.UnitTest/TypeTests/TimeSpanTests.cs

@@ -0,0 +1,82 @@
+using System;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+namespace S7.Net.UnitTest.TypeTests
+{
+    public static class TimeSpanTests
+    {
+        private static readonly TimeSpan SampleTimeSpan = new TimeSpan(12, 0, 59, 37, 856);
+
+        private static readonly byte[] SampleByteArray = { 0x3E, 0x02, 0xE8, 0x00 };
+
+        private static readonly byte[] SpecMinByteArray = { 0x80, 0x00, 0x00, 0x00 };
+        
+        private static readonly byte[] SpecMaxByteArray = { 0x7F, 0xFF, 0xFF, 0xFF };
+
+        [TestClass]
+        public class FromByteArray
+        {
+            [TestMethod]
+            public void Sample()
+            {
+                AssertFromByteArrayEquals(SampleTimeSpan, SampleByteArray);
+            }
+
+            [TestMethod]
+            public void SpecMinimum()
+            {
+                AssertFromByteArrayEquals(Types.TimeSpan.SpecMinimumTimeSpan, SpecMinByteArray);
+            }
+
+            [TestMethod]
+            public void SpecMaximum()
+            {
+                AssertFromByteArrayEquals(Types.TimeSpan.SpecMaximumTimeSpan, SpecMaxByteArray);
+            }
+
+            private static void AssertFromByteArrayEquals(TimeSpan expected, params byte[] bytes)
+            {
+                Assert.AreEqual(expected, Types.TimeSpan.FromByteArray(bytes));
+            }
+        }
+
+        [TestClass]
+        public class ToByteArray
+        {
+            [TestMethod]
+            public void Sample()
+            {
+                AssertToByteArrayEquals(SampleTimeSpan, SampleByteArray);
+            }
+
+            [TestMethod]
+            public void SpecMinimum()
+            {
+                AssertToByteArrayEquals(Types.TimeSpan.SpecMinimumTimeSpan, SpecMinByteArray);
+            }
+
+            [TestMethod]
+            public void SpecMaximum()
+            {
+                AssertToByteArrayEquals(Types.TimeSpan.SpecMaximumTimeSpan, SpecMaxByteArray);
+            }
+
+            [TestMethod, ExpectedException(typeof(ArgumentOutOfRangeException))]
+            public void ThrowsOnTimeBeforeSpecMinimum()
+            {
+                Types.TimeSpan.ToByteArray(TimeSpan.FromDays(-25));
+            }
+
+            [TestMethod, ExpectedException(typeof(ArgumentOutOfRangeException))]
+            public void ThrowsOnTimeAfterSpecMaximum()
+            {
+                Types.TimeSpan.ToByteArray(new TimeSpan(30, 15, 15, 15, 15));
+            }
+
+            private static void AssertToByteArrayEquals(TimeSpan value, params byte[] expected)
+            {
+                CollectionAssert.AreEqual(expected, Types.TimeSpan.ToByteArray(value));
+            }
+        }
+    }
+}

S7.Net/COTP.cs

@@ -55,22 +55,7 @@ namespace S7.Net
             /// See: https://tools.ietf.org/html/rfc905
             /// </summary>
             /// <param name="stream">The socket to read from</param>
-            /// <returns>COTP DPDU instance</returns>
-            public static TPDU Read(Stream stream)
-            {
-                var tpkt = TPKT.Read(stream);
-                if (tpkt.Length == 0)
-                {
-                    throw new TPDUInvalidException("No protocol data received");
-                }
-                return new TPDU(tpkt);
-            }
-
-            /// <summary>
-            /// Reads COTP TPDU (Transport protocol data unit) from the network stream
-            /// See: https://tools.ietf.org/html/rfc905
-            /// </summary>
-            /// <param name="stream">The socket to read from</param>
+            /// <param name="cancellationToken">A cancellation token that can be used to cancel the asynchronous operation.</param>
             /// <returns>COTP DPDU instance</returns>
             public static async Task<TPDU> ReadAsync(Stream stream, CancellationToken cancellationToken)
             {
@@ -105,39 +90,10 @@ namespace S7.Net
             /// See: https://tools.ietf.org/html/rfc905
             /// </summary>
             /// <param name="stream">The stream to read from</param>
-            /// <returns>Data in TSDU</returns>
-            public static byte[] Read(Stream stream)
-            {
-                var segment = TPDU.Read(stream);
-
-                if (segment.LastDataUnit)
-                {
-                    return segment.Data;
-                }
-
-                // More segments are expected, prepare a buffer to store all data
-                var buffer = new byte[segment.Data.Length];
-                Array.Copy(segment.Data, buffer, segment.Data.Length);
-
-                while (!segment.LastDataUnit)
-                {
-                    segment = TPDU.Read(stream);
-                    var previousLength = buffer.Length;
-                    Array.Resize(ref buffer, buffer.Length + segment.Data.Length);
-                    Array.Copy(segment.Data, 0, buffer, previousLength, segment.Data.Length);
-                }
-
-                return buffer;
-            }
-
-            /// <summary>
-            /// Reads the full COTP TSDU (Transport service data unit)
-            /// See: https://tools.ietf.org/html/rfc905
-            /// </summary>
-            /// <param name="stream">The stream to read from</param>
+            /// <param name="cancellationToken">A cancellation token that can be used to cancel the asynchronous operation.</param>
             /// <returns>Data in TSDU</returns>
             public static async Task<byte[]> ReadAsync(Stream stream, CancellationToken cancellationToken)
-            {                
+            {
                 var segment = await TPDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
 
                 if (segment.LastDataUnit)

S7.Net/Conversion.cs

@@ -138,19 +138,59 @@ namespace S7.Net
 
         /// <summary>
         /// Helper to get a bit value given a byte and the bit index.
-        /// Example: DB1.DBX0.5 -> var bytes = ReadBytes(DB1.DBW0); bool bit = bytes[0].SelectBit(5); 
+        /// <br/>
+        /// <example>
+        ///   Get the bit at DB1.DBX0.5:
+        ///   <code>
+        ///     byte data = ReadByte("DB1.DBB0");
+        ///     bool bit = data.SelectBit(5);
+        ///   </code>
+        /// </example>
         /// </summary>
-        /// <param name="data"></param>
-        /// <param name="bitPosition"></param>
-        /// <returns></returns>
-        public static bool SelectBit(this byte data, int bitPosition)
+        /// <param name="data">The data to get from.</param>
+        /// <param name="index">The zero-based index of the bit to get.</param>
+        /// <returns>The Boolean value will get.</returns>
+        public static bool SelectBit(this byte data, int index)
         {
-            int mask = 1 << bitPosition;
+            int mask = 1 << index;
             int result = data & mask;
 
             return (result != 0);
         }
 
+        /// <summary>
+        /// Helper to set a bit value to the given byte at the bit index.
+        /// <br/>
+        /// <example>
+        ///   Set the bit at index 4:
+        ///   <code>
+        ///     byte data = 0;
+        ///     data.SetBit(4, true);
+        ///   </code>
+        /// </example>
+        /// </summary>
+        /// <param name="data">The data to be modified.</param>
+        /// <param name="index">The zero-based index of the bit to set.</param>
+        /// <param name="value">The Boolean value to assign to the bit.</param>
+        public static void SetBit(this ref byte data, int index, bool value)
+        {
+            if ((uint)index > 7)
+            {
+                return;
+            }
+
+            if (value)
+            {
+                byte mask = (byte)(1 << index);
+                data |= mask;
+            }
+            else
+            {
+                byte mask = (byte)~(1 << index);
+                data &= mask;
+            }
+        }
+
         /// <summary>
         /// Converts from ushort value to short value; it's used to retrieve negative values from words
         /// </summary>

S7.Net/Enums.cs

@@ -15,6 +15,11 @@
         /// </summary>
         Logo0BA8 = 1,
 
+        /// <summary>
+        /// S7 200 Smart
+        /// </summary>
+        S7200Smart = 2,
+
         /// <summary>
         /// S7 300 cpu type
         /// </summary>
@@ -197,10 +202,20 @@
         /// DateTIme variable type
         /// </summary>
         DateTime,
+        
+        /// <summary>
+        /// IEC date (legacy) variable type
+        /// </summary>
+        Date,
 
         /// <summary>
         /// DateTimeLong variable type
         /// </summary>
-        DateTimeLong
+        DateTimeLong,
+        
+        /// <summary>
+        /// S7 TIME variable type - serialized as S7 DInt and deserialized as C# TimeSpan 
+        /// </summary>
+        Time
     }
 }

S7.Net/Helper/DateTimeExtensions.cs

@@ -0,0 +1,23 @@
+using System;
+using S7.Net.Types;
+using DateTime = System.DateTime;
+
+namespace S7.Net.Helper
+{
+    public static class DateTimeExtensions
+    {
+        public static ushort GetDaysSinceIecDateStart(this DateTime dateTime)
+        {
+            if (dateTime < Date.IecMinDate)
+            {
+                throw new ArgumentOutOfRangeException($"DateTime must be at least {Date.IecMinDate:d}");
+            }
+            if (dateTime > Date.IecMaxDate)
+            {
+                throw new ArgumentOutOfRangeException($"DateTime must be lower than {Date.IecMaxDate:d}");
+            }
+
+            return (ushort)(dateTime - Date.IecMinDate).TotalDays;
+        }
+    }
+}

S7.Net/Helper/MemoryStreamExtension.cs

@@ -1,6 +1,10 @@
-
+using System;
+using System.Buffers;
+using System.IO;
+
 namespace S7.Net.Helper
 {
+#if !NET5_0_OR_GREATER
     internal static class MemoryStreamExtension
     {
         /// <summary>
@@ -10,9 +14,25 @@ namespace S7.Net.Helper
         /// </summary>
         /// <param name="stream"></param>
         /// <param name="value"></param>
-        public static void WriteByteArray(this System.IO.MemoryStream stream, byte[] value)
+        public static void Write(this MemoryStream stream, byte[] value)
         {
             stream.Write(value, 0, value.Length);
         }
+
+        /// <summary>
+        /// Helper function to write the whole content of the given byte span to a memory stream.
+        /// </summary>
+        /// <param name="stream"></param>
+        /// <param name="value"></param>
+        public static void Write(this MemoryStream stream, ReadOnlySpan<byte> value)
+        {
+            byte[] buffer = ArrayPool<byte>.Shared.Rent(value.Length);
+
+            value.CopyTo(buffer);
+            stream.Write(buffer, 0, value.Length);
+
+            ArrayPool<byte>.Shared.Return(buffer);
+        }
     }
+#endif
 }

S7.Net/Internal/TaskQueue.cs

@@ -0,0 +1,28 @@
+using System;
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace S7.Net.Internal
+{
+    internal class TaskQueue
+    {
+        private static readonly object Sentinel = new object();
+
+        private Task prev = Task.FromResult(Sentinel);
+
+        public async Task<T> Enqueue<T>(Func<Task<T>> action)
+        {
+            var tcs = new TaskCompletionSource<object>();
+            await Interlocked.Exchange(ref prev, tcs.Task).ConfigureAwait(false);
+
+            try
+            {
+                return await action.Invoke().ConfigureAwait(false);
+            }
+            finally
+            {
+                tcs.SetResult(Sentinel);
+            }
+        }
+    }
+}

S7.Net/PLC.cs

@@ -1,7 +1,9 @@
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
 using System.Net.Sockets;
+using S7.Net.Internal;
 using S7.Net.Protocol;
 using S7.Net.Types;
 
@@ -13,14 +15,24 @@ namespace S7.Net
     /// </summary>
     public partial class Plc : IDisposable
     {
-        private const int CONNECTION_TIMED_OUT_ERROR_CODE = 10060;
+        /// <summary>
+        /// The default port for the S7 protocol.
+        /// </summary>
+        public const int DefaultPort = 102;
+
+        /// <summary>
+        /// The default timeout (in milliseconds) used for <see cref="P:ReadTimeout"/> and <see cref="P:WriteTimeout"/>.
+        /// </summary>
+        public const int DefaultTimeout = 10_000;
+
+        private readonly TaskQueue queue = new TaskQueue();
 
         //TCP connection to device
         private TcpClient? tcpClient;
         private NetworkStream? _stream;
 
-        private int readTimeout = 0; // default no timeout
-        private int writeTimeout = 0; // default no timeout
+        private int readTimeout = DefaultTimeout; // default no timeout
+        private int writeTimeout = DefaultTimeout; // default no timeout
 
         /// <summary>
         /// IP address of the PLC
@@ -32,6 +44,11 @@ namespace S7.Net
         /// </summary>
         public int Port { get; }
 
+        /// <summary>
+        /// The TSAP addresses used during the connection request.
+        /// </summary>
+        public TsapPair TsapPair { get; set; }
+
         /// <summary>
         /// CPU type of the PLC
         /// </summary>
@@ -104,25 +121,14 @@ namespace S7.Net
         /// </summary>
         /// <param name="cpu">CpuType of the PLC (select from the enum)</param>
         /// <param name="ip">Ip address of the PLC</param>
-        /// <param name="port">Port address of the PLC, default 102</param>
         /// <param name="rack">rack of the PLC, usually it's 0, but check in the hardware configuration of Step7 or TIA portal</param>
         /// <param name="slot">slot of the CPU of the PLC, usually it's 2 for S7300-S7400, 0 for S7-1200 and S7-1500.
         ///  If you use an external ethernet card, this must be set accordingly.</param>
-        public Plc(CpuType cpu, string ip, int port, Int16 rack, Int16 slot)
+        public Plc(CpuType cpu, string ip, Int16 rack, Int16 slot)
+            : this(cpu, ip, DefaultPort, rack, slot)
         {
-            if (!Enum.IsDefined(typeof(CpuType), cpu))
-                throw new ArgumentException($"The value of argument '{nameof(cpu)}' ({cpu}) is invalid for Enum type '{typeof(CpuType).Name}'.", nameof(cpu));
-
-            if (string.IsNullOrEmpty(ip))
-                throw new ArgumentException("IP address must valid.", nameof(ip));
-
-            CPU = cpu;
-            IP = ip;
-            Port = port;
-            Rack = rack;
-            Slot = slot;
-            MaxPDUSize = 240;
         }
+
         /// <summary>
         /// Creates a PLC object with all the parameters needed for connections.
         /// For S7-1200 and S7-1500, the default is rack = 0 and slot = 0.
@@ -131,23 +137,51 @@ namespace S7.Net
         /// </summary>
         /// <param name="cpu">CpuType of the PLC (select from the enum)</param>
         /// <param name="ip">Ip address of the PLC</param>
+        /// <param name="port">Port number used for the connection, default 102.</param>
         /// <param name="rack">rack of the PLC, usually it's 0, but check in the hardware configuration of Step7 or TIA portal</param>
         /// <param name="slot">slot of the CPU of the PLC, usually it's 2 for S7300-S7400, 0 for S7-1200 and S7-1500.
         ///  If you use an external ethernet card, this must be set accordingly.</param>
-        public Plc(CpuType cpu, string ip, Int16 rack, Int16 slot)
+        public Plc(CpuType cpu, string ip, int port, Int16 rack, Int16 slot)
+            : this(ip, port, TsapPair.GetDefaultTsapPair(cpu, rack, slot))
         {
             if (!Enum.IsDefined(typeof(CpuType), cpu))
-                throw new ArgumentException($"The value of argument '{nameof(cpu)}' ({cpu}) is invalid for Enum type '{typeof(CpuType).Name}'.", nameof(cpu));
+                throw new ArgumentException(
+                    $"The value of argument '{nameof(cpu)}' ({cpu}) is invalid for Enum type '{typeof(CpuType).Name}'.",
+                    nameof(cpu));
 
+            CPU = cpu;
+            Rack = rack;
+            Slot = slot;
+        }
+
+        /// <summary>
+        /// Creates a PLC object with all the parameters needed for connections.
+        /// For S7-1200 and S7-1500, the default is rack = 0 and slot = 0.
+        /// You need slot > 0 if you are connecting to external ethernet card (CP).
+        /// For S7-300 and S7-400 the default is rack = 0 and slot = 2.
+        /// </summary>
+        /// <param name="ip">Ip address of the PLC</param>
+        /// <param name="tsapPair">The TSAP addresses used for the connection request.</param>
+        public Plc(string ip, TsapPair tsapPair) : this(ip, DefaultPort, tsapPair)
+        {
+        }
+
+        /// <summary>
+        /// Creates a PLC object with all the parameters needed for connections. Use this constructor
+        /// if you want to manually override the TSAP addresses used during the connection request.
+        /// </summary>
+        /// <param name="ip">Ip address of the PLC</param>
+        /// <param name="port">Port number used for the connection, default 102.</param>
+        /// <param name="tsapPair">The TSAP addresses used for the connection request.</param>
+        public Plc(string ip, int port, TsapPair tsapPair)
+        {
             if (string.IsNullOrEmpty(ip))
                 throw new ArgumentException("IP address must valid.", nameof(ip));
 
-            CPU = cpu;
             IP = ip;
-            Port = 102;
-            Rack = rack;
-            Slot = slot;
+            Port = port;
             MaxPDUSize = 240;
+            TsapPair = tsapPair;
         }
 
         /// <summary>
@@ -158,6 +192,7 @@ namespace S7.Net
             if (tcpClient != null)
             {
                 if (tcpClient.Connected) tcpClient.Close();
+                tcpClient = null; // Can not reuse TcpClient once connection gets closed.
             }
         }
 
@@ -242,6 +277,16 @@ namespace S7.Net
             }
         }
 
+        private Stream GetStreamIfAvailable()
+        {
+            if (_stream == null)
+            {
+                throw new PlcException(ErrorCode.ConnectionError, "Plc is not connected");
+            }
+
+            return _stream;
+        }
+
         #region IDisposable Support
         private bool disposedValue = false; // To detect redundant calls
 

S7.Net/PLCExceptions.cs

@@ -6,7 +6,7 @@ using System.Runtime.Serialization;
 
 namespace S7.Net
 {
-    internal class WrongNumberOfBytesException : Exception
+    public class WrongNumberOfBytesException : Exception
     {
         public WrongNumberOfBytesException() : base()
         {
@@ -27,7 +27,7 @@ namespace S7.Net
         #endif
     }
 
-    internal class InvalidAddressException : Exception
+    public class InvalidAddressException : Exception
     {
         public InvalidAddressException() : base ()
         {
@@ -48,7 +48,7 @@ namespace S7.Net
         #endif
     }
 
-    internal class InvalidVariableTypeException : Exception
+    public class InvalidVariableTypeException : Exception
     {
         public InvalidVariableTypeException() : base()
         {
@@ -69,7 +69,7 @@ namespace S7.Net
         #endif
     }
 
-    internal class TPKTInvalidException : Exception
+    public class TPKTInvalidException : Exception
     {
         public TPKTInvalidException() : base()
         {
@@ -90,7 +90,7 @@ namespace S7.Net
         #endif
     }
 
-    internal class TPDUInvalidException : Exception
+    public class TPDUInvalidException : Exception
     {
         public TPDUInvalidException() : base()
         {

S7.Net/PLCHelpers.cs

@@ -1,7 +1,6 @@
 using S7.Net.Helper;
 using S7.Net.Protocol.S7;
 using S7.Net.Types;
-using System;
 using System.Collections.Generic;
 using System.Linq;
 using DateTime = S7.Net.Types.DateTime;
@@ -10,29 +9,104 @@ namespace S7.Net
 {
     public partial class Plc
     {
-        /// <summary>
-        /// Creates the header to read bytes from the PLC
-        /// </summary>
-        /// <param name="amount"></param>
-        /// <returns></returns>
-        private static void BuildHeaderPackage(System.IO.MemoryStream stream, int amount = 1)
+        private static void WriteTpktHeader(System.IO.MemoryStream stream, int length)
         {
-            //header size = 19 bytes
-            stream.WriteByteArray(new byte[] { 0x03, 0x00 });
-            //complete package size
-            stream.WriteByteArray(Types.Int.ToByteArray((short)(19 + (12 * amount))));
-            stream.WriteByteArray(new byte[] { 0x02, 0xf0, 0x80, 0x32, 0x01, 0x00, 0x00, 0x00, 0x00 });
-            //data part size
-            stream.WriteByteArray(Types.Word.ToByteArray((ushort)(2 + (amount * 12))));
-            stream.WriteByteArray(new byte[] { 0x00, 0x00, 0x04 });
+            stream.Write(new byte[] { 0x03, 0x00 });
+            stream.Write(Word.ToByteArray((ushort) length));
+        }
+
+        private static void WriteDataHeader(System.IO.MemoryStream stream)
+        {
+            stream.Write(new byte[] { 0x02, 0xf0, 0x80 });
+        }
+
+        private static void WriteS7Header(System.IO.MemoryStream stream, byte messageType, int parameterLength, int dataLength)
+        {
+            stream.WriteByte(0x32); // S7 protocol ID
+            stream.WriteByte(messageType); // Message type
+            stream.Write(new byte[] { 0x00, 0x00 }); // Reserved
+            stream.Write(new byte[] { 0x00, 0x00 }); // PDU ref
+            stream.Write(Word.ToByteArray((ushort) parameterLength));
+            stream.Write(Word.ToByteArray((ushort) dataLength));
+        }
+
+        /// <summary>
+        /// Creates the header to read bytes from the PLC.
+        /// </summary>
+        /// <param name="stream">The stream to write to.</param>
+        /// <param name="amount">The number of items to read.</param>
+        private static void WriteReadHeader(System.IO.MemoryStream stream, int amount = 1)
+        {
+            // Header size 19, 12 bytes per item
+            WriteTpktHeader(stream, 19 + 12 * amount);
+            WriteDataHeader(stream);
+            WriteS7Header(stream, 0x01, 2 + 12 * amount, 0);
+            // Function code: read request
+            stream.WriteByte(0x04);
             //amount of requests
             stream.WriteByte((byte)amount);
         }
 
+        private static void WriteUserDataHeader(System.IO.MemoryStream stream, int parameterLength, int dataLength)
+        {
+            const byte s7MessageTypeUserData = 0x07;
+
+            WriteTpktHeader(stream, 17 + parameterLength + dataLength);
+            WriteDataHeader(stream);
+            WriteS7Header(stream, s7MessageTypeUserData, parameterLength, dataLength);
+        }
+
+        private static void WriteUserDataRequest(System.IO.MemoryStream stream, byte functionGroup, byte subFunction, int dataLength)
+        {
+            WriteUserDataHeader(stream, 8, dataLength);
+
+            // Parameter
+            const byte userDataMethodRequest = 0x11;
+            const byte userDataTypeRequest = 0x4;
+
+            // Parameter head
+            stream.Write(new byte[] { 0x00, 0x01, 0x12 });
+            // Parameter length
+            stream.WriteByte(0x04);
+            // Method
+            stream.WriteByte(userDataMethodRequest);
+            // Type / function group
+            stream.WriteByte((byte)(userDataTypeRequest << 4 | (functionGroup & 0x0f)));
+            // Subfunction
+            stream.WriteByte(subFunction);
+            // Sequence number
+            stream.WriteByte(0);
+        }
+
+        private static void WriteSzlReadRequest(System.IO.MemoryStream stream, ushort szlId, ushort szlIndex)
+        {
+            // Parameter
+            const byte szlFunctionGroupCpuFunctions = 0b100;
+            const byte subFunctionReadSzl = 0x01;
+
+            WriteUserDataRequest(stream, szlFunctionGroupCpuFunctions, subFunctionReadSzl, 8);
+
+            // Data
+            const byte success = 0xff;
+            const byte transportSizeOctetString = 0x09;
+
+            // Return code
+            stream.WriteByte(success);
+            // Transport size
+            stream.WriteByte(transportSizeOctetString);
+            // Length
+            stream.Write(Word.ToByteArray(4));
+            // SZL-ID
+            stream.Write(Word.ToByteArray(szlId));
+            // SZL-Index
+            stream.Write(Word.ToByteArray(szlIndex));
+        }
+
         /// <summary>
         /// Create the bytes-package to request data from the PLC. You have to specify the memory type (dataType),
         /// the address of the memory, the address of the byte and the bytes count.
         /// </summary>
+        /// <param name="stream">The stream to write the read data request to.</param>
         /// <param name="dataType">MemoryType (DB, Timer, Counter, etc.)</param>
         /// <param name="db">Address of the memory to be read</param>
         /// <param name="startByteAdr">Start address of the byte</param>
@@ -41,7 +115,7 @@ namespace S7.Net
         private static void BuildReadDataRequestPackage(System.IO.MemoryStream stream, DataType dataType, int db, int startByteAdr, int count = 1)
         {
             //single data req = 12
-            stream.WriteByteArray(new byte[] { 0x12, 0x0a, 0x10 });
+            stream.Write(new byte[] { 0x12, 0x0a, 0x10 });
             switch (dataType)
             {
                 case DataType.Timer:
@@ -53,8 +127,8 @@ namespace S7.Net
                     break;
             }
 
-            stream.WriteByteArray(Word.ToByteArray((ushort)(count)));
-            stream.WriteByteArray(Word.ToByteArray((ushort)(db)));
+            stream.Write(Word.ToByteArray((ushort)(count)));
+            stream.Write(Word.ToByteArray((ushort)(db)));
             stream.WriteByte((byte)dataType);
             var overflow = (int)(startByteAdr * 8 / 0xffffU); // handles words with address bigger than 8191
             stream.WriteByte((byte)overflow);
@@ -62,10 +136,10 @@ namespace S7.Net
             {
                 case DataType.Timer:
                 case DataType.Counter:
-                    stream.WriteByteArray(Types.Word.ToByteArray((ushort)(startByteAdr)));
+                    stream.Write(Word.ToByteArray((ushort)(startByteAdr)));
                     break;
                 default:
-                    stream.WriteByteArray(Types.Word.ToByteArray((ushort)((startByteAdr) * 8)));
+                    stream.Write(Word.ToByteArray((ushort)((startByteAdr) * 8)));
                     break;
             }
         }
@@ -168,6 +242,24 @@ namespace S7.Net
                     {
                         return DateTimeLong.ToArray(bytes);
                     }
+                case VarType.Time:
+                    if (varCount == 1)
+                    {
+                        return TimeSpan.FromByteArray(bytes);
+                    }
+                    else
+                    {
+                        return TimeSpan.ToArray(bytes);
+                    }
+                case VarType.Date:
+                    if (varCount == 1)
+                    {
+                        return Date.FromByteArray(bytes);
+                    }
+                    else
+                    {
+                        return Date.ToArray(bytes);
+                    }
                 default:
                     return null;
             }
@@ -197,10 +289,12 @@ namespace S7.Net
                 case VarType.Timer:
                 case VarType.Int:
                 case VarType.Counter:
+                case VarType.Date:
                     return varCount * 2;
                 case VarType.DWord:
                 case VarType.DInt:
                 case VarType.Real:
+                case VarType.Time:
                     return varCount * 4;
                 case VarType.LReal:
                 case VarType.DateTime:
@@ -242,8 +336,8 @@ namespace S7.Net
                 // next Item
                 offset += byteCnt;
 
-                // Fill byte in response when bytecount is odd
-                if (dataItem.Count % 2 != 0 && (dataItem.VarType == VarType.Byte || dataItem.VarType == VarType.Bit))
+                // Always align to even offset
+                if (offset % 2 != 0)
                     offset++;
             }
         }
@@ -253,7 +347,7 @@ namespace S7.Net
             int packageSize = 19 + (dataItems.Count * 12);
             var package = new System.IO.MemoryStream(packageSize);
 
-            BuildHeaderPackage(package, dataItems.Count);
+            WriteReadHeader(package, dataItems.Count);
 
             foreach (var dataItem in dataItems)
             {
@@ -262,5 +356,15 @@ namespace S7.Net
 
             return package.ToArray();
         }
+
+        private static byte[] BuildSzlReadRequestPackage(ushort szlId, ushort szlIndex)
+        {
+            var stream = new System.IO.MemoryStream();
+
+            WriteSzlReadRequest(stream, szlId, szlIndex);
+            stream.SetLength(stream.Position);
+
+            return stream.ToArray();
+        }
     }
 }

S7.Net/Plc.Clock.cs

@@ -0,0 +1,92 @@
+using System;
+using System.IO;
+using System.Linq;
+using S7.Net.Helper;
+using S7.Net.Types;
+using DateTime = System.DateTime;
+
+namespace S7.Net;
+
+partial class Plc
+{
+    private const byte SzlFunctionGroupTimers = 0x07;
+    private const byte SzlSubFunctionReadClock = 0x01;
+    private const byte SzlSubFunctionWriteClock = 0x02;
+    private const byte TransportSizeOctetString = 0x09;
+    private const int PduErrOffset = 20;
+    private const int UserDataResultOffset = PduErrOffset + 2;
+
+    /// <summary>
+    /// The length in bytes of DateTime stored in the PLC.
+    /// </summary>
+    private const int DateTimeLength = 10;
+
+    private static byte[] BuildClockReadRequest()
+    {
+        var stream = new MemoryStream();
+
+        WriteUserDataRequest(stream, SzlFunctionGroupTimers, SzlSubFunctionReadClock, 4);
+        stream.Write(new byte[] { 0x0a, 0x00, 0x00, 0x00 });
+
+        stream.SetLength(stream.Position);
+        return stream.ToArray();
+    }
+
+    private static DateTime ParseClockReadResponse(byte[] message)
+    {
+        const int udLenOffset = UserDataResultOffset + 2;
+        const int udValueOffset = udLenOffset + 2;
+        const int dateTimeSkip = 2;
+
+        AssertPduResult(message);
+        AssertUserDataResult(message, 0xff);
+
+        var len = Word.FromByteArray(message.Skip(udLenOffset).Take(2).ToArray());
+        if (len != DateTimeLength)
+        {
+            throw new Exception($"Unexpected response length {len}, expected {DateTimeLength}.");
+        }
+
+        // Skip first 2 bytes from date time value because DateTime.FromByteArray doesn't parse them.
+        return Types.DateTime.FromByteArray(message.Skip(udValueOffset + dateTimeSkip)
+            .Take(DateTimeLength - dateTimeSkip).ToArray());
+    }
+
+    private static byte[] BuildClockWriteRequest(DateTime value)
+    {
+        var stream = new MemoryStream();
+
+        WriteUserDataRequest(stream, SzlFunctionGroupTimers, SzlSubFunctionWriteClock, 14);
+        stream.Write(new byte[] { 0xff, TransportSizeOctetString, 0x00, DateTimeLength });
+        // Start of DateTime value, DateTime.ToByteArray only serializes the final 8 bytes
+        stream.Write(new byte[] { 0x00, 0x19 });
+        stream.Write(Types.DateTime.ToByteArray(value));
+
+        stream.SetLength(stream.Position);
+        return stream.ToArray();
+    }
+
+    private static void ParseClockWriteResponse(byte[] message)
+    {
+        AssertPduResult(message);
+        AssertUserDataResult(message, 0x0a);
+    }
+
+    private static void AssertPduResult(byte[] message)
+    {
+        var pduErr = Word.FromByteArray(message.Skip(PduErrOffset).Take(2).ToArray());
+        if (pduErr != 0)
+        {
+            throw new Exception($"Response from PLC indicates error 0x{pduErr:X4}.");
+        }
+    }
+
+    private static void AssertUserDataResult(byte[] message, byte expected)
+    {
+        var dtResult = message[UserDataResultOffset];
+        if (dtResult != expected)
+        {
+            throw new Exception($"Response from PLC was 0x{dtResult:X2}, expected 0x{expected:X2}.");
+        }
+    }
+}

S7.Net/PlcAsynchronous.cs

@@ -1,11 +1,11 @@
 using S7.Net.Types;
 using System;
 using System.Collections.Generic;
+using System.IO;
 using System.Linq;
 using System.Net.Sockets;
 using System.Threading.Tasks;
 using S7.Net.Protocol;
-using System.IO;
 using System.Threading;
 using S7.Net.Protocol.S7;
 
@@ -25,51 +25,62 @@ namespace S7.Net
         /// <returns>A task that represents the asynchronous open operation.</returns>
         public async Task OpenAsync(CancellationToken cancellationToken = default)
         {
-            var stream = await ConnectAsync().ConfigureAwait(false);
+            var stream = await ConnectAsync(cancellationToken).ConfigureAwait(false);
             try
             {
-                cancellationToken.ThrowIfCancellationRequested();
-                await EstablishConnection(stream, cancellationToken).ConfigureAwait(false);
-                _stream = stream;
+                await queue.Enqueue(async () =>
+                {
+                    cancellationToken.ThrowIfCancellationRequested();
+                    await EstablishConnection(stream, cancellationToken).ConfigureAwait(false);
+                    _stream = stream;
+
+                    return default(object);
+                }).ConfigureAwait(false);
             }
-            catch(Exception)
+            catch (Exception)
             {
                 stream.Dispose();
                 throw;
             }
         }
 
-        private async Task<NetworkStream> ConnectAsync()
+        private async Task<NetworkStream> ConnectAsync(CancellationToken cancellationToken)
         {
             tcpClient = new TcpClient();
             ConfigureConnection();
+
+#if NET5_0_OR_GREATER
+            await tcpClient.ConnectAsync(IP, Port, cancellationToken).ConfigureAwait(false);
+#else
             await tcpClient.ConnectAsync(IP, Port).ConfigureAwait(false);
+#endif
             return tcpClient.GetStream();
         }
 
-        private async Task EstablishConnection(NetworkStream stream, CancellationToken cancellationToken)
+        private async Task EstablishConnection(Stream stream, CancellationToken cancellationToken)
         {
             await RequestConnection(stream, cancellationToken).ConfigureAwait(false);
             await SetupConnection(stream, cancellationToken).ConfigureAwait(false);
         }
 
-        private async Task RequestConnection(NetworkStream stream, CancellationToken cancellationToken)
+        private async Task RequestConnection(Stream stream, CancellationToken cancellationToken)
         {
-            var requestData = ConnectionRequest.GetCOTPConnectionRequest(CPU, Rack, Slot);
-            await stream.WriteAsync(requestData, 0, requestData.Length).ConfigureAwait(false);
-            var response = await COTP.TPDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
+            var requestData = ConnectionRequest.GetCOTPConnectionRequest(TsapPair);
+            var response = await NoLockRequestTpduAsync(stream, requestData, cancellationToken).ConfigureAwait(false);
+
             if (response.PDUType != COTP.PduType.ConnectionConfirmed)
             {
                 throw new InvalidDataException("Connection request was denied", response.TPkt.Data, 1, 0x0d);
             }
         }
 
-        private async Task SetupConnection(NetworkStream stream, CancellationToken cancellationToken)
+        private async Task SetupConnection(Stream stream, CancellationToken cancellationToken)
         {
             var setupData = GetS7ConnectionSetup();
-            await stream.WriteAsync(setupData, 0, setupData.Length).ConfigureAwait(false);
 
-            var s7data = await COTP.TSDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
+            var s7data = await NoLockRequestTsduAsync(stream, setupData, 0, setupData.Length, cancellationToken)
+                .ConfigureAwait(false);
+
             if (s7data.Length < 2)
                 throw new WrongNumberOfBytesException("Not enough data received in response to Communication Setup");
 
@@ -84,7 +95,6 @@ namespace S7.Net
             MaxPDUSize = s7data[18] * 256 + s7data[19];
         }
 
-
         /// <summary>
         /// Reads a number of bytes from a DB starting from a specified index. This handles more than 200 bytes with multiple requests.
         /// If the read was not successful, check LastErrorCode or LastErrorString.
@@ -99,20 +109,38 @@ namespace S7.Net
         public async Task<byte[]> ReadBytesAsync(DataType dataType, int db, int startByteAdr, int count, CancellationToken cancellationToken = default)
         {
             var resultBytes = new byte[count];
-            int index = 0;
-            while (count > 0)
-            {
-                //This works up to MaxPDUSize-1 on SNAP7. But not MaxPDUSize-0.
-                var maxToRead = Math.Min(count, MaxPDUSize - 18);
-                await ReadBytesWithSingleRequestAsync(dataType, db, startByteAdr + index, resultBytes, index, maxToRead, cancellationToken).ConfigureAwait(false);
-                count -= maxToRead;
-                index += maxToRead;
-            }
+
+            await ReadBytesAsync(resultBytes, dataType, db, startByteAdr, cancellationToken).ConfigureAwait(false);
+
             return resultBytes;
         }
 
         /// <summary>
-        /// Read and decode a certain number of bytes of the "VarType" provided. 
+        /// Reads a number of bytes from a DB starting from a specified index. This handles more than 200 bytes with multiple requests.
+        /// If the read was not successful, check LastErrorCode or LastErrorString.
+        /// </summary>
+        /// <param name="buffer">Buffer to receive the read bytes. The <see cref="Memory{T}.Length"/> determines the number of bytes to read.</param>
+        /// <param name="dataType">Data type of the memory area, can be DB, Timer, Counter, Merker(Memory), Input, Output.</param>
+        /// <param name="db">Address of the memory area (if you want to read DB1, this is set to 1). This must be set also for other memory area types: counters, timers,etc.</param>
+        /// <param name="startByteAdr">Start byte address. If you want to read DB1.DBW200, this is 200.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is None.
+        /// Please note that cancellation is advisory/cooperative and will not lead to immediate cancellation in all cases.</param>
+        /// <returns>Returns the bytes in an array</returns>
+        public async Task ReadBytesAsync(Memory<byte> buffer, DataType dataType, int db, int startByteAdr, CancellationToken cancellationToken = default)
+        {
+            int index = 0;
+            while (buffer.Length > 0)
+            {
+                //This works up to MaxPDUSize-1 on SNAP7. But not MaxPDUSize-0.
+                var maxToRead = Math.Min(buffer.Length, MaxPDUSize - 18);
+                await ReadBytesWithSingleRequestAsync(dataType, db, startByteAdr + index, buffer.Slice(0, maxToRead), cancellationToken).ConfigureAwait(false);
+                buffer = buffer.Slice(maxToRead);
+                index += maxToRead;
+            }
+        }
+
+        /// <summary>
+        /// Read and decode a certain number of bytes of the "VarType" provided.
         /// This can be used to read multiple consecutive variables of the same type (Word, DWord, Int, etc).
         /// If the read was not successful, check LastErrorCode or LastErrorString.
         /// </summary>
@@ -179,10 +207,10 @@ namespace S7.Net
         }
 
         /// <summary>
-        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC. 
+        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC.
         /// This reads only properties, it doesn't read private variable or public variable without {get;set;} specified.
         /// </summary>
-        /// <param name="sourceClass">Instance of the class that will store the values</param>       
+        /// <param name="sourceClass">Instance of the class that will store the values</param>
         /// <param name="db">Index of the DB; es.: 1 is for DB1</param>
         /// <param name="startByteAdr">Start byte address. If you want to read DB1.DBW200, this is 200.</param>
         /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is None.
@@ -205,7 +233,7 @@ namespace S7.Net
         }
 
         /// <summary>
-        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC. 
+        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC.
         /// This reads only properties, it doesn't read private variable or public variable without {get;set;} specified. To instantiate the class defined by the generic
         /// type, the class needs a default constructor.
         /// </summary>
@@ -221,7 +249,7 @@ namespace S7.Net
         }
 
         /// <summary>
-        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC. 
+        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC.
         /// This reads only properties, it doesn't read private variable or public variable without {get;set;} specified.
         /// </summary>
         /// <typeparam name="T">The class that will be instantiated</typeparam>
@@ -245,10 +273,10 @@ namespace S7.Net
         }
 
         /// <summary>
-        /// Reads multiple vars in a single request. 
+        /// Reads multiple vars in a single request.
         /// You have to create and pass a list of DataItems and you obtain in response the same list with the values.
         /// Values are stored in the property "Value" of the dataItem and are already converted.
-        /// If you don't want the conversion, just create a dataItem of bytes. 
+        /// If you don't want the conversion, just create a dataItem of bytes.
         /// The number of DataItems as well as the total size of the requested data can not exceed a certain limit (protocol restriction).
         /// </summary>
         /// <param name="dataItems">List of dataitems that contains the list of variables that must be read.</param>
@@ -256,18 +284,15 @@ namespace S7.Net
         /// Please note that cancellation is advisory/cooperative and will not lead to immediate cancellation in all cases.</param>
         public async Task<List<DataItem>> ReadMultipleVarsAsync(List<DataItem> dataItems, CancellationToken cancellationToken = default)
         {
-            //Snap7 seems to choke on PDU sizes above 256 even if snap7 
+            //Snap7 seems to choke on PDU sizes above 256 even if snap7
             //replies with bigger PDU size in connection setup.
             AssertPduSizeForRead(dataItems);
 
-            var stream = GetStreamIfAvailable();
-
             try
             {
                 var dataToSend = BuildReadRequestPackage(dataItems.Select(d => DataItem.GetDataItemAddress(d)).ToList());
-                await stream.WriteAsync(dataToSend, 0, dataToSend.Length).ConfigureAwait(false);
+                var s7data = await RequestTsduAsync(dataToSend, cancellationToken);
 
-                var s7data = await COTP.TSDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
 
                 ParseDataIntoDataItems(s7data, dataItems);
@@ -287,6 +312,48 @@ namespace S7.Net
             return dataItems;
         }
 
+        /// <summary>
+        /// Read the PLC clock value.
+        /// </summary>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is None.
+        /// Please note that cancellation is advisory/cooperative and will not lead to immediate cancellation in all cases.</param>
+        /// <returns>A task that represents the asynchronous operation, with it's result set to the current PLC time on completion.</returns>
+        public async Task<System.DateTime> ReadClockAsync(CancellationToken cancellationToken = default)
+        {
+            var request = BuildClockReadRequest();
+            var response = await RequestTsduAsync(request, cancellationToken);
+
+            return ParseClockReadResponse(response);
+        }
+
+        /// <summary>
+        /// Write the PLC clock value.
+        /// </summary>
+        /// <param name="value">The date and time to set the PLC clock to</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is None.
+        /// Please note that cancellation is advisory/cooperative and will not lead to immediate cancellation in all cases.</param>
+        /// <returns>A task that represents the asynchronous operation.</returns>
+        public async Task WriteClockAsync(System.DateTime value, CancellationToken cancellationToken = default)
+        {
+            var request = BuildClockWriteRequest(value);
+            var response = await RequestTsduAsync(request, cancellationToken);
+
+            ParseClockWriteResponse(response);
+        }
+
+        /// <summary>
+        /// Read the current status from the PLC. A value of 0x08 indicates the PLC is in run status, regardless of the PLC type.
+        /// </summary>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is None.
+        /// Please note that cancellation is advisory/cooperative and will not lead to immediate cancellation in all cases.</param>
+        /// <returns>A task that represents the asynchronous operation, with it's result set to the current PLC status on completion.</returns>
+        public async Task<byte> ReadStatusAsync(CancellationToken cancellationToken = default)
+        {
+            var dataToSend = BuildSzlReadRequestPackage(0x0424, 0);
+            var s7data = await RequestTsduAsync(dataToSend, cancellationToken);
+
+            return (byte) (s7data[37] & 0x0f);
+        }
 
         /// <summary>
         /// Write a number of bytes from a DB starting from a specified index. This handles more than 200 bytes with multiple requests.
@@ -299,15 +366,30 @@ namespace S7.Net
         /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is None.
         /// Please note that cancellation is advisory/cooperative and will not lead to immediate cancellation in all cases.</param>
         /// <returns>A task that represents the asynchronous write operation.</returns>
-        public async Task WriteBytesAsync(DataType dataType, int db, int startByteAdr, byte[] value, CancellationToken cancellationToken = default)
+        public Task WriteBytesAsync(DataType dataType, int db, int startByteAdr, byte[] value, CancellationToken cancellationToken = default)
+        {
+            return WriteBytesAsync(dataType, db, startByteAdr, value.AsMemory(), cancellationToken);
+        }
+
+        /// <summary>
+        /// Write a number of bytes from a DB starting from a specified index. This handles more than 200 bytes with multiple requests.
+        /// If the write was not successful, check LastErrorCode or LastErrorString.
+        /// </summary>
+        /// <param name="dataType">Data type of the memory area, can be DB, Timer, Counter, Merker(Memory), Input, Output.</param>
+        /// <param name="db">Address of the memory area (if you want to read DB1, this is set to 1). This must be set also for other memory area types: counters, timers,etc.</param>
+        /// <param name="startByteAdr">Start byte address. If you want to write DB1.DBW200, this is 200.</param>
+        /// <param name="value">Bytes to write. If more than 200, multiple requests will be made.</param>
+        /// <param name="cancellationToken">The token to monitor for cancellation requests. The default value is None.
+        /// Please note that cancellation is advisory/cooperative and will not lead to immediate cancellation in all cases.</param>
+        /// <returns>A task that represents the asynchronous write operation.</returns>
+        public async Task WriteBytesAsync(DataType dataType, int db, int startByteAdr, ReadOnlyMemory<byte> value, CancellationToken cancellationToken = default)
         {
             int localIndex = 0;
-            int count = value.Length;
-            while (count > 0)
+            while (value.Length > 0)
             {
-                var maxToWrite = (int)Math.Min(count, MaxPDUSize - 35);
-                await WriteBytesWithASingleRequestAsync(dataType, db, startByteAdr + localIndex, value, localIndex, maxToWrite, cancellationToken).ConfigureAwait(false);
-                count -= maxToWrite;
+                var maxToWrite = (int)Math.Min(value.Length, MaxPDUSize - 35);
+                await WriteBytesWithASingleRequestAsync(dataType, db, startByteAdr + localIndex, value.Slice(0, maxToWrite), cancellationToken).ConfigureAwait(false);
+                value = value.Slice(maxToWrite);
                 localIndex += maxToWrite;
             }
         }
@@ -389,7 +471,6 @@ namespace S7.Net
 
         /// <summary>
         /// Writes a single variable from the PLC, takes in input strings like "DB1.DBX0.0", "DB20.DBD200", "MB20", "T45", etc.
-        /// If the write was not successful, check <see cref="LastErrorCode"/> or <see cref="LastErrorString"/>.
         /// </summary>
         /// <param name="variable">Input strings like "DB1.DBX0.0", "DB20.DBD200", "MB20", "T45", etc.</param>
         /// <param name="value">Value to be written to the PLC</param>
@@ -433,17 +514,14 @@ namespace S7.Net
             await WriteBytesAsync(DataType.DataBlock, db, startByteAdr, bytes, cancellationToken).ConfigureAwait(false);
         }
 
-        private async Task ReadBytesWithSingleRequestAsync(DataType dataType, int db, int startByteAdr, byte[] buffer, int offset, int count, CancellationToken cancellationToken)
+        private async Task ReadBytesWithSingleRequestAsync(DataType dataType, int db, int startByteAdr, Memory<byte> buffer, CancellationToken cancellationToken)
         {
-            var stream = GetStreamIfAvailable();
+            var dataToSend = BuildReadRequestPackage(new[] { new DataItemAddress(dataType, db, startByteAdr, buffer.Length) });
 
-            var dataToSend = BuildReadRequestPackage(new [] { new DataItemAddress(dataType, db, startByteAdr, count)});
-            await stream.WriteAsync(dataToSend, 0, dataToSend.Length, cancellationToken);
+            var s7data = await RequestTsduAsync(dataToSend, cancellationToken);
+            AssertReadResponse(s7data, buffer.Length);
 
-            var s7data = await COTP.TSDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
-            AssertReadResponse(s7data, count);
-
-            Array.Copy(s7data, 18, buffer, offset, count);
+            s7data.AsSpan(18, buffer.Length).CopyTo(buffer.Span);
         }
 
         /// <summary>
@@ -456,13 +534,11 @@ namespace S7.Net
         {
             AssertPduSizeForWrite(dataItems);
 
-            var stream = GetStreamIfAvailable();
-
             var message = new ByteArray();
             var length = S7WriteMultiple.CreateRequest(message, dataItems);
-            await stream.WriteAsync(message.Array, 0, length).ConfigureAwait(false);
 
-            var response = await COTP.TSDU.ReadAsync(stream, CancellationToken.None).ConfigureAwait(false);
+            var response = await RequestTsduAsync(message.Array, 0, length).ConfigureAwait(false);
+
             S7WriteMultiple.ParseResponse(response, response.Length, dataItems);
         }
 
@@ -473,18 +549,15 @@ namespace S7.Net
         /// <param name="db">Address of the memory area (if you want to read DB1, this is set to 1). This must be set also for other memory area types: counters, timers,etc.</param>
         /// <param name="startByteAdr">Start byte address. If you want to read DB1.DBW200, this is 200.</param>
         /// <param name="value">Bytes to write. The lenght of this parameter can't be higher than 200. If you need more, use recursion.</param>
+        /// <param name="cancellationToken">A cancellation token that can be used to cancel the asynchronous operation.</param>
         /// <returns>A task that represents the asynchronous write operation.</returns>
-        private async Task WriteBytesWithASingleRequestAsync(DataType dataType, int db, int startByteAdr, byte[] value, int dataOffset, int count, CancellationToken cancellationToken)
+        private async Task WriteBytesWithASingleRequestAsync(DataType dataType, int db, int startByteAdr, ReadOnlyMemory<byte> value, CancellationToken cancellationToken)
         {
-
             try
             {
-                var stream = GetStreamIfAvailable();
-                var dataToSend = BuildWriteBytesPackage(dataType, db, startByteAdr, value, dataOffset, count);
+                var dataToSend = BuildWriteBytesPackage(dataType, db, startByteAdr, value.Span);
+                var s7data = await RequestTsduAsync(dataToSend, cancellationToken).ConfigureAwait(false);
 
-                await stream.WriteAsync(dataToSend, 0, dataToSend.Length, cancellationToken).ConfigureAwait(false);
-
-                var s7data = await COTP.TSDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
             }
             catch (OperationCanceledException)
@@ -499,15 +572,11 @@ namespace S7.Net
 
         private async Task WriteBitWithASingleRequestAsync(DataType dataType, int db, int startByteAdr, int bitAdr, bool bitValue, CancellationToken cancellationToken)
         {
-            var stream = GetStreamIfAvailable();
-
             try
             {
                 var dataToSend = BuildWriteBitPackage(dataType, db, startByteAdr, bitValue, bitAdr);
+                var s7data = await RequestTsduAsync(dataToSend, cancellationToken).ConfigureAwait(false);
 
-                await stream.WriteAsync(dataToSend, 0, dataToSend.Length).ConfigureAwait(false);
-
-                var s7data = await COTP.TSDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
             }
             catch (OperationCanceledException)
@@ -520,13 +589,57 @@ namespace S7.Net
             }
         }
 
-        private Stream GetStreamIfAvailable()
+        private Task<byte[]> RequestTsduAsync(byte[] requestData, CancellationToken cancellationToken = default) =>
+            RequestTsduAsync(requestData, 0, requestData.Length, cancellationToken);
+
+        private Task<byte[]> RequestTsduAsync(byte[] requestData, int offset, int length, CancellationToken cancellationToken = default)
         {
-            if (_stream == null)
+            var stream = GetStreamIfAvailable();
+
+            return queue.Enqueue(() =>
+                NoLockRequestTsduAsync(stream, requestData, offset, length, cancellationToken));
+        }
+
+        private async Task<COTP.TPDU> NoLockRequestTpduAsync(Stream stream, byte[] requestData,
+            CancellationToken cancellationToken = default)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+            try
             {
-                throw new PlcException(ErrorCode.ConnectionError, "Plc is not connected");
+                using var closeOnCancellation = cancellationToken.Register(Close);
+                await stream.WriteAsync(requestData, 0, requestData.Length, cancellationToken).ConfigureAwait(false);
+                return await COTP.TPDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
+            }
+            catch (Exception exc)
+            {
+                if (exc is TPDUInvalidException || exc is TPKTInvalidException)
+                {
+                    Close();
+                }
+
+                throw;
+            }
+        }
+
+        private async Task<byte[]> NoLockRequestTsduAsync(Stream stream, byte[] requestData, int offset, int length,
+            CancellationToken cancellationToken = default)
+        {
+            cancellationToken.ThrowIfCancellationRequested();
+            try
+            {
+                using var closeOnCancellation = cancellationToken.Register(Close);
+                await stream.WriteAsync(requestData, offset, length, cancellationToken).ConfigureAwait(false);
+                return await COTP.TSDU.ReadAsync(stream, cancellationToken).ConfigureAwait(false);
+            }
+            catch (Exception exc)
+            {
+                if (exc is TPDUInvalidException || exc is TPKTInvalidException)
+                {
+                    Close();
+                }
+
+                throw;
             }
-            return _stream;
         }
     }
 }

S7.Net/PlcSynchronous.cs

@@ -2,8 +2,6 @@
 using System;
 using System.IO;
 using System.Collections.Generic;
-using System.Linq;
-using System.Net.Sockets;
 using S7.Net.Protocol;
 using S7.Net.Helper;
 
@@ -41,20 +39,36 @@ namespace S7.Net
         public byte[] ReadBytes(DataType dataType, int db, int startByteAdr, int count)
         {
             var result = new byte[count];
-            int index = 0;
-            while (count > 0)
-            {
-                //This works up to MaxPDUSize-1 on SNAP7. But not MaxPDUSize-0.
-                var maxToRead = Math.Min(count, MaxPDUSize - 18);
-                ReadBytesWithSingleRequest(dataType, db, startByteAdr + index, result, index, maxToRead);
-                count -= maxToRead;
-                index += maxToRead;
-            }
+
+            ReadBytes(result, dataType, db, startByteAdr);
+
             return result;
         }
 
         /// <summary>
-        /// Read and decode a certain number of bytes of the "VarType" provided. 
+        /// Reads a number of bytes from a DB starting from a specified index. This handles more than 200 bytes with multiple requests.
+        /// If the read was not successful, check LastErrorCode or LastErrorString.
+        /// </summary>
+        /// <param name="buffer">Buffer to receive the read bytes. The <see cref="Span{T}.Length"/> determines the number of bytes to read.</param>
+        /// <param name="dataType">Data type of the memory area, can be DB, Timer, Counter, Merker(Memory), Input, Output.</param>
+        /// <param name="db">Address of the memory area (if you want to read DB1, this is set to 1). This must be set also for other memory area types: counters, timers,etc.</param>
+        /// <param name="startByteAdr">Start byte address. If you want to read DB1.DBW200, this is 200.</param>
+        /// <returns>Returns the bytes in an array</returns>
+        public void ReadBytes(Span<byte> buffer, DataType dataType, int db, int startByteAdr)
+        {
+            int index = 0;
+            while (buffer.Length > 0)
+            {
+                //This works up to MaxPDUSize-1 on SNAP7. But not MaxPDUSize-0.
+                var maxToRead = Math.Min(buffer.Length, MaxPDUSize - 18);
+                ReadBytesWithSingleRequest(dataType, db, startByteAdr + index, buffer.Slice(0, maxToRead));
+                buffer = buffer.Slice(maxToRead);
+                index += maxToRead;
+            }
+        }
+
+        /// <summary>
+        /// Read and decode a certain number of bytes of the "VarType" provided.
         /// This can be used to read multiple consecutive variables of the same type (Word, DWord, Int, etc).
         /// If the read was not successful, check LastErrorCode or LastErrorString.
         /// </summary>
@@ -113,12 +127,11 @@ namespace S7.Net
             return ReadStruct(typeof(T), db, startByteAdr) as T?;
         }
 
-
         /// <summary>
-        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC. 
+        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC.
         /// This reads only properties, it doesn't read private variable or public variable without {get;set;} specified.
         /// </summary>
-        /// <param name="sourceClass">Instance of the class that will store the values</param>       
+        /// <param name="sourceClass">Instance of the class that will store the values</param>
         /// <param name="db">Index of the DB; es.: 1 is for DB1</param>
         /// <param name="startByteAdr">Start byte address. If you want to read DB1.DBW200, this is 200.</param>
         /// <returns>The number of read bytes</returns>
@@ -138,7 +151,7 @@ namespace S7.Net
         }
 
         /// <summary>
-        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC. 
+        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC.
         /// This reads only properties, it doesn't read private variable or public variable without {get;set;} specified. To instantiate the class defined by the generic
         /// type, the class needs a default constructor.
         /// </summary>
@@ -152,7 +165,7 @@ namespace S7.Net
         }
 
         /// <summary>
-        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC. 
+        /// Reads all the bytes needed to fill a class in C#, starting from a certain address, and set all the properties values to the value that are read from the PLC.
         /// This reads only properties, it doesn't read private variable or public variable without {get;set;} specified.
         /// </summary>
         /// <typeparam name="T">The class that will be instantiated</typeparam>
@@ -180,17 +193,29 @@ namespace S7.Net
         /// <param name="startByteAdr">Start byte address. If you want to write DB1.DBW200, this is 200.</param>
         /// <param name="value">Bytes to write. If more than 200, multiple requests will be made.</param>
         public void WriteBytes(DataType dataType, int db, int startByteAdr, byte[] value)
+        {
+            WriteBytes(dataType, db, startByteAdr, value.AsSpan());
+        }
+
+        /// <summary>
+        /// Write a number of bytes from a DB starting from a specified index. This handles more than 200 bytes with multiple requests.
+        /// If the write was not successful, check LastErrorCode or LastErrorString.
+        /// </summary>
+        /// <param name="dataType">Data type of the memory area, can be DB, Timer, Counter, Merker(Memory), Input, Output.</param>
+        /// <param name="db">Address of the memory area (if you want to read DB1, this is set to 1). This must be set also for other memory area types: counters, timers,etc.</param>
+        /// <param name="startByteAdr">Start byte address. If you want to write DB1.DBW200, this is 200.</param>
+        /// <param name="value">Bytes to write. If more than 200, multiple requests will be made.</param>
+        public void WriteBytes(DataType dataType, int db, int startByteAdr, ReadOnlySpan<byte> value)
         {
             int localIndex = 0;
-            int count = value.Length;
-            while (count > 0)
+            while (value.Length > 0)
             {
                 //TODO: Figure out how to use MaxPDUSize here
-                //Snap7 seems to choke on PDU sizes above 256 even if snap7 
+                //Snap7 seems to choke on PDU sizes above 256 even if snap7
                 //replies with bigger PDU size in connection setup.
-                var maxToWrite = Math.Min(count, MaxPDUSize - 28);//TODO tested only when the MaxPDUSize is 480
-                WriteBytesWithASingleRequest(dataType, db, startByteAdr + localIndex, value, localIndex, maxToWrite);
-                count -= maxToWrite;
+                var maxToWrite = Math.Min(value.Length, MaxPDUSize - 28);//TODO tested only when the MaxPDUSize is 480
+                WriteBytesWithASingleRequest(dataType, db, startByteAdr + localIndex, value.Slice(0, maxToWrite));
+                value = value.Slice(maxToWrite);
                 localIndex += maxToWrite;
             }
         }
@@ -264,7 +289,6 @@ namespace S7.Net
 
         /// <summary>
         /// Writes a single variable from the PLC, takes in input strings like "DB1.DBX0.0", "DB20.DBD200", "MB20", "T45", etc.
-        /// If the write was not successful, check <see cref="LastErrorCode"/> or <see cref="LastErrorString"/>.
         /// </summary>
         /// <param name="variable">Input strings like "DB1.DBX0.0", "DB20.DBD200", "MB20", "T45", etc.</param>
         /// <param name="value">Value to be written to the PLC</param>
@@ -296,25 +320,22 @@ namespace S7.Net
             WriteClassAsync(classValue, db, startByteAdr).GetAwaiter().GetResult();
         }
 
-        private void ReadBytesWithSingleRequest(DataType dataType, int db, int startByteAdr, byte[] buffer, int offset, int count)
+        private void ReadBytesWithSingleRequest(DataType dataType, int db, int startByteAdr, Span<byte> buffer)
         {
-            var stream = GetStreamIfAvailable();
             try
             {
                 // first create the header
-                int packageSize = 19 + 12; // 19 header + 12 for 1 request
-                var package = new System.IO.MemoryStream(packageSize);
-                BuildHeaderPackage(package);
+                const int packageSize = 19 + 12; // 19 header + 12 for 1 request
+                var dataToSend = new byte[packageSize];
+                var package = new MemoryStream(dataToSend);
+                WriteReadHeader(package);
                 // package.Add(0x02);  // datenart
-                BuildReadDataRequestPackage(package, dataType, db, startByteAdr, count);
+                BuildReadDataRequestPackage(package, dataType, db, startByteAdr, buffer.Length);
 
-                var dataToSend = package.ToArray();
-                stream.Write(dataToSend, 0, dataToSend.Length);
+                var s7data = RequestTsdu(dataToSend);
+                AssertReadResponse(s7data, buffer.Length);
 
-                var s7data = COTP.TSDU.Read(stream);
-                AssertReadResponse(s7data, count);
-
-                Array.Copy(s7data, 18, buffer, offset, count);
+                s7data.AsSpan(18, buffer.Length).CopyTo(buffer);
             }
             catch (Exception exc)
             {
@@ -331,26 +352,20 @@ namespace S7.Net
         {
             AssertPduSizeForWrite(dataItems);
 
-            var stream = GetStreamIfAvailable();
-
             var message = new ByteArray();
             var length = S7WriteMultiple.CreateRequest(message, dataItems);
-            stream.Write(message.Array, 0, length);
+            var response = RequestTsdu(message.Array, 0, length);
 
-            var response = COTP.TSDU.Read(stream);
             S7WriteMultiple.ParseResponse(response, response.Length, dataItems);
         }
 
-        private void WriteBytesWithASingleRequest(DataType dataType, int db, int startByteAdr, byte[] value, int dataOffset, int count)
+        private void WriteBytesWithASingleRequest(DataType dataType, int db, int startByteAdr, ReadOnlySpan<byte> value)
         {
             try
             {
-                var stream = GetStreamIfAvailable();
-                var dataToSend = BuildWriteBytesPackage(dataType, db, startByteAdr, value, dataOffset, count);
+                var dataToSend = BuildWriteBytesPackage(dataType, db, startByteAdr, value);
+                var s7data = RequestTsdu(dataToSend);
 
-                stream.Write(dataToSend, 0, dataToSend.Length);
-
-                var s7data = COTP.TSDU.Read(stream);
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
             }
             catch (Exception exc)
@@ -359,35 +374,37 @@ namespace S7.Net
             }
         }
 
-        private byte[] BuildWriteBytesPackage(DataType dataType, int db, int startByteAdr, byte[] value, int dataOffset, int count)
+        private byte[] BuildWriteBytesPackage(DataType dataType, int db, int startByteAdr, ReadOnlySpan<byte> value)
         {
-            int varCount = count;
+            int varCount = value.Length;
             // first create the header
             int packageSize = 35 + varCount;
-            var package = new MemoryStream(new byte[packageSize]);
+            var packageData = new byte[packageSize];
+            var package = new MemoryStream(packageData);
 
             package.WriteByte(3);
             package.WriteByte(0);
             //complete package size
-            package.WriteByteArray(Int.ToByteArray((short)packageSize));
-            package.WriteByteArray(new byte[] { 2, 0xf0, 0x80, 0x32, 1, 0, 0 });
-            package.WriteByteArray(Word.ToByteArray((ushort)(varCount - 1)));
-            package.WriteByteArray(new byte[] { 0, 0x0e });
-            package.WriteByteArray(Word.ToByteArray((ushort)(varCount + 4)));
-            package.WriteByteArray(new byte[] { 0x05, 0x01, 0x12, 0x0a, 0x10, 0x02 });
-            package.WriteByteArray(Word.ToByteArray((ushort)varCount));
-            package.WriteByteArray(Word.ToByteArray((ushort)(db)));
+            package.Write(Int.ToByteArray((short)packageSize));
+            // This overload doesn't allocate the byte array, it refers to assembly's static data segment
+            package.Write(new byte[] { 2, 0xf0, 0x80, 0x32, 1, 0, 0 });
+            package.Write(Word.ToByteArray((ushort)(varCount - 1)));
+            package.Write(new byte[] { 0, 0x0e });
+            package.Write(Word.ToByteArray((ushort)(varCount + 4)));
+            package.Write(new byte[] { 0x05, 0x01, 0x12, 0x0a, 0x10, 0x02 });
+            package.Write(Word.ToByteArray((ushort)varCount));
+            package.Write(Word.ToByteArray((ushort)(db)));
             package.WriteByte((byte)dataType);
             var overflow = (int)(startByteAdr * 8 / 0xffffU); // handles words with address bigger than 8191
             package.WriteByte((byte)overflow);
-            package.WriteByteArray(Word.ToByteArray((ushort)(startByteAdr * 8)));
-            package.WriteByteArray(new byte[] { 0, 4 });
-            package.WriteByteArray(Word.ToByteArray((ushort)(varCount * 8)));
+            package.Write(Word.ToByteArray((ushort)(startByteAdr * 8)));
+            package.Write(new byte[] { 0, 4 });
+            package.Write(Word.ToByteArray((ushort)(varCount * 8)));
 
             // now join the header and the data
-            package.Write(value, dataOffset, count);
+            package.Write(value);
 
-            return package.ToArray();
+            return packageData;
         }
 
         private byte[] BuildWriteBitPackage(DataType dataType, int db, int startByteAdr, bool bitValue, int bitAdr)
@@ -396,43 +413,40 @@ namespace S7.Net
             int varCount = 1;
             // first create the header
             int packageSize = 35 + varCount;
-            var package = new MemoryStream(new byte[packageSize]);
+            var packageData = new byte[packageSize];
+            var package = new MemoryStream(packageData);
 
             package.WriteByte(3);
             package.WriteByte(0);
             //complete package size
-            package.WriteByteArray(Int.ToByteArray((short)packageSize));
-            package.WriteByteArray(new byte[] { 2, 0xf0, 0x80, 0x32, 1, 0, 0 });
-            package.WriteByteArray(Word.ToByteArray((ushort)(varCount - 1)));
-            package.WriteByteArray(new byte[] { 0, 0x0e });
-            package.WriteByteArray(Word.ToByteArray((ushort)(varCount + 4)));
-            package.WriteByteArray(new byte[] { 0x05, 0x01, 0x12, 0x0a, 0x10, 0x01 }); //ending 0x01 is used for writing a sinlge bit
-            package.WriteByteArray(Word.ToByteArray((ushort)varCount));
-            package.WriteByteArray(Word.ToByteArray((ushort)(db)));
+            package.Write(Int.ToByteArray((short)packageSize));
+            package.Write(new byte[] { 2, 0xf0, 0x80, 0x32, 1, 0, 0 });
+            package.Write(Word.ToByteArray((ushort)(varCount - 1)));
+            package.Write(new byte[] { 0, 0x0e });
+            package.Write(Word.ToByteArray((ushort)(varCount + 4)));
+            package.Write(new byte[] { 0x05, 0x01, 0x12, 0x0a, 0x10, 0x01 }); //ending 0x01 is used for writing a sinlge bit
+            package.Write(Word.ToByteArray((ushort)varCount));
+            package.Write(Word.ToByteArray((ushort)(db)));
             package.WriteByte((byte)dataType);
             var overflow = (int)(startByteAdr * 8 / 0xffffU); // handles words with address bigger than 8191
             package.WriteByte((byte)overflow);
-            package.WriteByteArray(Word.ToByteArray((ushort)(startByteAdr * 8 + bitAdr)));
-            package.WriteByteArray(new byte[] { 0, 0x03 }); //ending 0x03 is used for writing a sinlge bit
-            package.WriteByteArray(Word.ToByteArray((ushort)(varCount)));
+            package.Write(Word.ToByteArray((ushort)(startByteAdr * 8 + bitAdr)));
+            package.Write(new byte[] { 0, 0x03 }); //ending 0x03 is used for writing a sinlge bit
+            package.Write(Word.ToByteArray((ushort)(varCount)));
 
             // now join the header and the data
-            package.WriteByteArray(value);
+            package.Write(value);
 
-            return package.ToArray();
+            return packageData;
         }
 
-
         private void WriteBitWithASingleRequest(DataType dataType, int db, int startByteAdr, int bitAdr, bool bitValue)
         {
-            var stream = GetStreamIfAvailable();
             try
             {
                 var dataToSend = BuildWriteBitPackage(dataType, db, startByteAdr, bitValue, bitAdr);
+                var s7data = RequestTsdu(dataToSend);
 
-                stream.Write(dataToSend, 0, dataToSend.Length);
-
-                var s7data = COTP.TSDU.Read(stream);
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
             }
             catch (Exception exc)
@@ -442,10 +456,10 @@ namespace S7.Net
         }
 
         /// <summary>
-        /// Reads multiple vars in a single request. 
+        /// Reads multiple vars in a single request.
         /// You have to create and pass a list of DataItems and you obtain in response the same list with the values.
         /// Values are stored in the property "Value" of the dataItem and are already converted.
-        /// If you don't want the conversion, just create a dataItem of bytes. 
+        /// If you don't want the conversion, just create a dataItem of bytes.
         /// The number of DataItems as well as the total size of the requested data can not exceed a certain limit (protocol restriction).
         /// </summary>
         /// <param name="dataItems">List of dataitems that contains the list of variables that must be read.</param>
@@ -453,24 +467,20 @@ namespace S7.Net
         {
             AssertPduSizeForRead(dataItems);
 
-            var stream = GetStreamIfAvailable();
-
             try
             {
                 // first create the header
                 int packageSize = 19 + (dataItems.Count * 12);
-                var package = new System.IO.MemoryStream(packageSize);
-                BuildHeaderPackage(package, dataItems.Count);
+                var dataToSend = new byte[packageSize];
+                var package = new MemoryStream(dataToSend);
+                WriteReadHeader(package, dataItems.Count);
                 // package.Add(0x02);  // datenart
                 foreach (var dataItem in dataItems)
                 {
                     BuildReadDataRequestPackage(package, dataItem.DataType, dataItem.DB, dataItem.StartByteAdr, VarTypeToByteLength(dataItem.VarType, dataItem.Count));
                 }
 
-                var dataToSend = package.ToArray();
-                stream.Write(dataToSend, 0, dataToSend.Length);
-
-                var s7data = COTP.TSDU.Read(stream); //TODO use Async
+                byte[] s7data = RequestTsdu(dataToSend);
 
                 ValidateResponseCode((ReadWriteErrorCode)s7data[14]);
 
@@ -481,5 +491,48 @@ namespace S7.Net
                 throw new PlcException(ErrorCode.ReadData, exc);
             }
         }
+
+        /// <summary>
+        /// Read the PLC clock value.
+        /// </summary>
+        /// <returns>The current PLC time.</returns>
+        public System.DateTime ReadClock()
+        {
+            var request = BuildClockReadRequest();
+            var response = RequestTsdu(request);
+
+            return ParseClockReadResponse(response);
+        }
+
+        /// <summary>
+        /// Write the PLC clock value.
+        /// </summary>
+        /// <param name="value">The date and time to set the PLC clock to.</param>
+        public void WriteClock(System.DateTime value)
+        {
+            var request = BuildClockWriteRequest(value);
+            var response = RequestTsdu(request);
+
+            ParseClockWriteResponse(response);
+        }
+
+        /// <summary>
+        /// Read the current status from the PLC. A value of 0x08 indicates the PLC is in run status, regardless of the PLC type.
+        /// </summary>
+        /// <returns>The current PLC status.</returns>
+        public byte ReadStatus()
+        {
+            var dataToSend = BuildSzlReadRequestPackage(0x0424, 0);
+            var s7data = RequestTsdu(dataToSend);
+
+            return (byte) (s7data[37] & 0x0f);
+        }
+
+        private byte[] RequestTsdu(byte[] requestData) => RequestTsdu(requestData, 0, requestData.Length);
+
+        private byte[] RequestTsdu(byte[] requestData, int offset, int length)
+        {
+            return RequestTsduAsync(requestData, offset, length).GetAwaiter().GetResult();
+        }
     }
 }

S7.Net/Protocol/ConnectionRequest.cs

@@ -1,68 +1,27 @@
-using System;
-
-namespace S7.Net.Protocol
+namespace S7.Net.Protocol
 {
     internal static class ConnectionRequest
     {
-        public static byte[] GetCOTPConnectionRequest(CpuType cpu, Int16 rack, Int16 slot)
+        public static byte[] GetCOTPConnectionRequest(TsapPair tsapPair)
         {
             byte[] bSend1 = {
                     3, 0, 0, 22, //TPKT
                     17,     //COTP Header Length
-                    224,    //Connect Request 
+                    224,    //Connect Request
                     0, 0,   //Destination Reference
                     0, 46,  //Source Reference
                     0,      //Flags
                     193,    //Parameter Code (src-tasp)
                     2,      //Parameter Length
-                    1, 0,   //Source TASP
+                    tsapPair.Local.FirstByte, tsapPair.Local.SecondByte,   //Source TASP
                     194,    //Parameter Code (dst-tasp)
                     2,      //Parameter Length
-                    3, 0,   //Destination TASP
+                    tsapPair.Remote.FirstByte, tsapPair.Remote.SecondByte,   //Destination TASP
                     192,    //Parameter Code (tpdu-size)
                     1,      //Parameter Length
                     10      //TPDU Size (2^10 = 1024)
                 };
 
-            switch (cpu)
-            {
-                case CpuType.S7200:
-                    //S7200: Chr(193) & Chr(2) & Chr(16) & Chr(0) 'Eigener Tsap
-                    bSend1[13] = 0x10;
-                    bSend1[14] = 0x00;
-                    //S7200: Chr(194) & Chr(2) & Chr(16) & Chr(0) 'Fremder Tsap
-                    bSend1[17] = 0x10;
-                    bSend1[18] = 0x00;
-                    break;
-                case CpuType.Logo0BA8:
-                    // These values are taken from NodeS7, it's not verified if these are
-                    // exact requirements to connect to the Logo0BA8.
-                    bSend1[13] = 0x01;
-                    bSend1[14] = 0x00;
-                    bSend1[17] = 0x01;
-                    bSend1[18] = 0x02;
-                    break;
-                case CpuType.S71200:
-                case CpuType.S7300:
-                case CpuType.S7400:
-                    //S7300: Chr(193) & Chr(2) & Chr(1) & Chr(0)  'Eigener Tsap
-                    bSend1[13] = 0x01;
-                    bSend1[14] = 0x00;
-                    //S7300: Chr(194) & Chr(2) & Chr(3) & Chr(2)  'Fremder Tsap
-                    bSend1[17] = 0x03;
-                    bSend1[18] = (byte) ((rack << 5) | (int) slot);
-                    break;
-                case CpuType.S71500:
-                    // Eigener Tsap
-                    bSend1[13] = 0x10;
-                    bSend1[14] = 0x02;
-                    // Fredmer Tsap
-                    bSend1[17] = 0x03;
-                    bSend1[18] = (byte) ((rack << 5) | (int) slot);
-                    break;
-                default:
-                    throw new Exception("Wrong CPU Type Secified");
-            }
             return bSend1;
         }
     }

S7.Net/Protocol/Serialization.cs

@@ -26,6 +26,11 @@ namespace S7.Net.Protocol
                     _ => Types.String.ToByteArray(s, dataItem.Count)
                 };
 
+            if (dataItem.VarType == VarType.Date)
+            {
+                return Date.ToByteArray((System.DateTime)dataItem.Value);
+            }
+
             return SerializeValue(dataItem.Value);
         }
 

S7.Net/Protocol/Tsap.cs

@@ -0,0 +1,31 @@
+namespace S7.Net.Protocol
+{
+    /// <summary>
+    /// Provides a representation of the Transport Service Access Point, or TSAP in short. TSAP's are used
+    /// to specify a client and server address. For most PLC types a default TSAP is available that allows
+    /// connection from any IP and can be calculated using the rack and slot numbers.
+    /// </summary>
+    public struct Tsap
+    {
+        /// <summary>
+        /// First byte of the TSAP.
+        /// </summary>
+        public byte FirstByte { get; set; }
+
+        /// <summary>
+        /// Second byte of the TSAP.
+        /// </summary>
+        public byte SecondByte { get; set; }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="Tsap" /> class using the specified values.
+        /// </summary>
+        /// <param name="firstByte">The first byte of the TSAP.</param>
+        /// <param name="secondByte">The second byte of the TSAP.</param>
+        public Tsap(byte firstByte, byte secondByte)
+        {
+            FirstByte = firstByte;
+            SecondByte = secondByte;
+        }
+    }
+}

S7.Net/Protocol/TsapPair.cs

@@ -0,0 +1,96 @@
+using System;
+
+namespace S7.Net.Protocol
+{
+    /// <summary>
+    /// Implements a pair of TSAP addresses used to connect to a PLC.
+    /// </summary>
+    public class TsapPair
+    {
+        /// <summary>
+        /// The local <see cref="Tsap" />.
+        /// </summary>
+        public Tsap Local { get; set; }
+
+        /// <summary>
+        /// The remote <see cref="Tsap" />
+        /// </summary>
+        public Tsap Remote { get; set; }
+
+        /// <summary>
+        /// Initializes a new instance of the <see cref="TsapPair" /> class using the specified local and
+        /// remote TSAP.
+        /// </summary>
+        /// <param name="local">The local TSAP.</param>
+        /// <param name="remote">The remote TSAP.</param>
+        public TsapPair(Tsap local, Tsap remote)
+        {
+            Local = local;
+            Remote = remote;
+        }
+
+        /// <summary>
+        /// Builds a <see cref="TsapPair" /> that can be used to connect to a PLC using the default connection
+        /// addresses.
+        /// </summary>
+        /// <remarks>
+        /// The remote TSAP is constructed using <code>new Tsap(0x03, (byte) ((rack &lt;&lt; 5) | slot))</code>.
+        /// </remarks>
+        /// <param name="cpuType">The CPU type of the PLC.</param>
+        /// <param name="rack">The rack of the PLC's network card.</param>
+        /// <param name="slot">The slot of the PLC's network card.</param>
+        /// <returns>A TSAP pair that matches the given parameters.</returns>
+        /// <exception cref="ArgumentOutOfRangeException">The <paramref name="cpuType"/> is invalid.
+        ///
+        /// -or-
+        ///
+        /// The <paramref name="rack"/> parameter is less than 0.
+        ///
+        /// -or-
+        ///
+        /// The <paramref name="rack"/> parameter is greater than 15.
+        ///
+        /// -or-
+        ///
+        /// The <paramref name="slot"/> parameter is less than 0.
+        ///
+        /// -or-
+        ///
+        /// The <paramref name="slot"/> parameter is greater than 15.</exception>
+        public static TsapPair GetDefaultTsapPair(CpuType cpuType, int rack, int slot)
+        {
+            if (rack < 0) throw InvalidRackOrSlot(rack, nameof(rack), "minimum", 0);
+            if (rack > 0x0F) throw InvalidRackOrSlot(rack, nameof(rack), "maximum", 0x0F);
+
+            if (slot < 0) throw InvalidRackOrSlot(slot, nameof(slot), "minimum", 0);
+            if (slot > 0x0F) throw InvalidRackOrSlot(slot, nameof(slot), "maximum", 0x0F);
+
+            switch (cpuType)
+            {
+                case CpuType.S7200:
+                    return new TsapPair(new Tsap(0x10, 0x00), new Tsap(0x10, 0x01));
+                case CpuType.Logo0BA8:
+                    // The actual values are probably on a per-project basis
+                    return new TsapPair(new Tsap(0x01, 0x00), new Tsap(0x01, 0x02));
+                case CpuType.S7200Smart:
+                case CpuType.S71200:
+                case CpuType.S71500:
+                case CpuType.S7300:
+                case CpuType.S7400:
+                    // Testing with S7 1500 shows only the remote TSAP needs to match. This might differ for other
+                    // PLC types.
+                    return new TsapPair(new Tsap(0x01, 0x00), new Tsap(0x03, (byte) ((rack << 5) | slot)));
+                default:
+                    throw new ArgumentOutOfRangeException(nameof(cpuType), "Invalid CPU Type specified");
+            }
+        }
+
+        private static ArgumentOutOfRangeException InvalidRackOrSlot(int value, string name, string extrema,
+            int extremaValue)
+        {
+            return new ArgumentOutOfRangeException(name,
+                $"Invalid {name} value specified (decimal: {value}, hexadecimal: {value:X}), {extrema} value " +
+                $"is {extremaValue} (decimal) or {extremaValue:X} (hexadecimal).");
+        }
+    }
+}

S7.Net/S7.Net.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   
   <PropertyGroup>
-    <TargetFrameworks>net452;netstandard2.0;netstandard1.3</TargetFrameworks>
+    <TargetFrameworks>net452;net462;netstandard2.0;netstandard1.3;net5.0;net6.0;net7.0</TargetFrameworks>
     <SignAssembly>true</SignAssembly>
     <AssemblyOriginatorKeyFile>Properties\S7.Net.snk</AssemblyOriginatorKeyFile>
     <InternalsVisibleTo>S7.Net.UnitTest</InternalsVisibleTo>
@@ -15,17 +15,22 @@
     <RepositoryType>git</RepositoryType>
     <PackageTags>PLC Siemens Communication S7</PackageTags>
     <Copyright>Derek Heiser 2015</Copyright>
-    <LangVersion>8.0</LangVersion>
+    <LangVersion>latest</LangVersion>
     <Nullable>Enable</Nullable>
     <DebugType>portable</DebugType>
     <IncludeSymbols>true</IncludeSymbols>
     <SymbolPackageFormat>snupkg</SymbolPackageFormat>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
+    <NoWarn>$(NoWarn);CS1591;NETSDK1138</NoWarn>
   </PropertyGroup>
 
-  <PropertyGroup Condition="'$(TargetFramework)' == 'net452' Or '$(TargetFramework)' == 'netstandard2.0' ">
+  <PropertyGroup Condition="'$(TargetFramework)' == 'net452' Or '$(TargetFramework)' == 'net462' Or '$(TargetFramework)' == 'netstandard2.0' ">
     <DefineConstants>NET_FULL</DefineConstants>
   </PropertyGroup>
+
+  <ItemGroup Condition="'$(TargetFramework)' != 'net5.0' And '$(TargetFramework)' != 'net6.0' And '$(TargetFramework)' != 'net7.0'">
+    <PackageReference Include="System.Memory" Version="4.5.5" />
+  </ItemGroup>
   
   <ItemGroup>
     <PackageReference Include="Microsoft.SourceLink.GitHub" Version="1.0.0" PrivateAssets="All" />

S7.Net/StreamExtensions.cs

@@ -39,6 +39,7 @@ namespace S7.Net
         /// <param name="buffer">the buffer to read into</param>
         /// <param name="offset">the offset in the buffer to read into</param>
         /// <param name="count">the amount of bytes to read into the buffer</param>
+        /// <param name="cancellationToken">A cancellation token that can be used to cancel the asynchronous operation.</param>
         /// <returns>returns the amount of read bytes</returns>
         public static async Task<int> ReadExactAsync(this Stream stream, byte[] buffer, int offset, int count, CancellationToken cancellationToken)
         {

S7.Net/TPKT.cs

@@ -25,38 +25,11 @@ namespace S7.Net
             Data = data;
         }
 
-        /// <summary>
-        /// Reads a TPKT from the socket
-        /// </summary>
-        /// <param name="stream">The stream to read from</param>
-        /// <returns>TPKT Instance</returns>
-        public static TPKT Read(Stream stream)
-        {
-            var buf = new byte[4];
-            int len = stream.ReadExact(buf, 0, 4);
-            if (len < 4) throw new TPKTInvalidException($"TPKT header is incomplete / invalid. Received Bytes: {len} expected: {buf.Length}");
-            var version = buf[0];
-            var reserved1 = buf[1];
-            var length = buf[2] * 256 + buf[3]; //BigEndian
-
-            var data = new byte[length - 4];
-            len = stream.ReadExact(data, 0, data.Length);
-            if (len < data.Length)
-                throw new TPKTInvalidException($"TPKT payload is incomplete / invalid. Received Bytes: {len} expected: {data.Length}");
-
-            return new TPKT
-            (
-                version: version,
-                reserved1: reserved1,
-                length: length,
-                data: data
-            );
-        }
-
         /// <summary>
         /// Reads a TPKT from the socket Async
         /// </summary>
         /// <param name="stream">The stream to read from</param>
+        /// <param name="cancellationToken">A cancellation token that can be used to cancel the asynchronous operation.</param>
         /// <returns>Task TPKT Instace</returns>
         public static async Task<TPKT> ReadAsync(Stream stream, CancellationToken cancellationToken)
         {

S7.Net/Types/Class.cs

@@ -2,6 +2,7 @@
 using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;
+using System.Runtime.InteropServices;
 
 namespace S7.Net.Types
 {
@@ -25,7 +26,7 @@ namespace S7.Net.Types
 
         }
 
-        private static double GetIncreasedNumberOfBytes(double numBytes, Type type)
+        private static double GetIncreasedNumberOfBytes(double numBytes, Type type, PropertyInfo? propertyInfo)
         {
             switch (type.Name)
             {
@@ -38,32 +39,33 @@ namespace S7.Net.Types
                     break;
                 case "Int16":
                 case "UInt16":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
+                    IncrementToEven(ref numBytes);
                     numBytes += 2;
                     break;
                 case "Int32":
                 case "UInt32":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
+                    IncrementToEven(ref numBytes);
                     numBytes += 4;
                     break;
                 case "Single":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
+                    IncrementToEven(ref numBytes);
                     numBytes += 4;
                     break;
                 case "Double":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
+                    IncrementToEven(ref numBytes);
                     numBytes += 8;
                     break;
+                case "String":
+                    S7StringAttribute? attribute = propertyInfo?.GetCustomAttributes<S7StringAttribute>().SingleOrDefault();
+                    if (attribute == default(S7StringAttribute))
+                        throw new ArgumentException("Please add S7StringAttribute to the string field");
+
+                    IncrementToEven(ref numBytes);
+                    numBytes += attribute.ReservedLengthInBytes;
+                    break;
                 default:
-                    var propertyClass = Activator.CreateInstance(type);
+                    var propertyClass = Activator.CreateInstance(type) ??
+                        throw new ArgumentException($"Failed to create instance of type {type}.", nameof(type));
                     numBytes = GetClassSize(propertyClass, numBytes, true);
                     break;
             }
@@ -75,6 +77,8 @@ namespace S7.Net.Types
         /// Gets the size of the class in bytes.
         /// </summary>
         /// <param name="instance">An instance of the class</param>
+        /// <param name="numBytes">The offset of the current field.</param>
+        /// <param name="isInnerProperty"><see langword="true" /> if this property belongs to a class being serialized as member of the class requested for serialization; otherwise, <see langword="false" />.</param>
         /// <returns>the number of bytes</returns>
         public static double GetClassSize(object instance, double numBytes = 0.0, bool isInnerProperty = false)
         {
@@ -83,8 +87,10 @@ namespace S7.Net.Types
             {
                 if (property.PropertyType.IsArray)
                 {
-                    Type elementType = property.PropertyType.GetElementType();
-                    Array array = (Array)property.GetValue(instance, null);
+                    Type elementType = property.PropertyType.GetElementType()!;
+                    Array array = (Array?) property.GetValue(instance, null) ??
+                        throw new ArgumentException($"Property {property.Name} on {instance} must have a non-null value to get it's size.", nameof(instance));
+
                     if (array.Length <= 0)
                     {
                         throw new Exception("Cannot determine size of class, because an array is defined which has no fixed size greater than zero.");
@@ -93,12 +99,12 @@ namespace S7.Net.Types
                     IncrementToEven(ref numBytes);
                     for (int i = 0; i < array.Length; i++)
                     {
-                        numBytes = GetIncreasedNumberOfBytes(numBytes, elementType);
+                        numBytes = GetIncreasedNumberOfBytes(numBytes, elementType, property);
                     }
                 }
                 else
                 {
-                    numBytes = GetIncreasedNumberOfBytes(numBytes, property.PropertyType);
+                    numBytes = GetIncreasedNumberOfBytes(numBytes, property.PropertyType, property);
                 }
             }
             if (false == isInnerProperty)
@@ -111,7 +117,7 @@ namespace S7.Net.Types
             return numBytes;
         }
 
-        private static object? GetPropertyValue(Type propertyType, byte[] bytes, ref double numBytes)
+        private static object? GetPropertyValue(Type propertyType, PropertyInfo? propertyInfo, byte[] bytes, ref double numBytes)
         {
             object? value = null;
 
@@ -133,50 +139,35 @@ namespace S7.Net.Types
                     numBytes++;
                     break;
                 case "Int16":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
+                    IncrementToEven(ref numBytes);
                     // hier auswerten
                     ushort source = Word.FromBytes(bytes[(int)numBytes + 1], bytes[(int)numBytes]);
                     value = source.ConvertToShort();
                     numBytes += 2;
                     break;
                 case "UInt16":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
+                    IncrementToEven(ref numBytes);
                     // hier auswerten
                     value = Word.FromBytes(bytes[(int)numBytes + 1], bytes[(int)numBytes]);
                     numBytes += 2;
                     break;
                 case "Int32":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
-                    // hier auswerten
-                    uint sourceUInt = DWord.FromBytes(bytes[(int)numBytes + 3],
-                                                                       bytes[(int)numBytes + 2],
-                                                                       bytes[(int)numBytes + 1],
-                                                                       bytes[(int)numBytes + 0]);
+                    IncrementToEven(ref numBytes);
+                    var wordBuffer = new byte[4];
+                    Array.Copy(bytes, (int)numBytes, wordBuffer, 0, wordBuffer.Length);
+                    uint sourceUInt = DWord.FromByteArray(wordBuffer);
                     value = sourceUInt.ConvertToInt();
                     numBytes += 4;
                     break;
                 case "UInt32":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
-                    // hier auswerten
-                    value = DWord.FromBytes(
-                        bytes[(int)numBytes],
-                        bytes[(int)numBytes + 1],
-                        bytes[(int)numBytes + 2],
-                        bytes[(int)numBytes + 3]);
+                    IncrementToEven(ref numBytes);
+                    var wordBuffer2 = new byte[4];
+                    Array.Copy(bytes, (int)numBytes, wordBuffer2, 0, wordBuffer2.Length);
+                    value = DWord.FromByteArray(wordBuffer2);
                     numBytes += 4;
                     break;
                 case "Single":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
+                    IncrementToEven(ref numBytes);
                     // hier auswerten
                     value = Real.FromByteArray(
                         new byte[] {
@@ -187,17 +178,35 @@ namespace S7.Net.Types
                     numBytes += 4;
                     break;
                 case "Double":
-                    numBytes = Math.Ceiling(numBytes);
-                    if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
-                        numBytes++;
+                    IncrementToEven(ref numBytes);
                     var buffer = new byte[8];
                     Array.Copy(bytes, (int)numBytes, buffer, 0, 8);
                     // hier auswerten
                     value = LReal.FromByteArray(buffer);
                     numBytes += 8;
                     break;
+                case "String":
+                    S7StringAttribute? attribute = propertyInfo?.GetCustomAttributes<S7StringAttribute>().SingleOrDefault();
+                    if (attribute == default(S7StringAttribute))
+                        throw new ArgumentException("Please add S7StringAttribute to the string field");
+
+                    IncrementToEven(ref numBytes);
+
+                    // get the value
+                    var sData = new byte[attribute.ReservedLengthInBytes];
+                    Array.Copy(bytes, (int)numBytes, sData, 0, sData.Length);
+                    value = attribute.Type switch
+                    {
+                        S7StringType.S7String => S7String.FromByteArray(sData),
+                        S7StringType.S7WString => S7WString.FromByteArray(sData),
+                        _ => throw new ArgumentException("Please use a valid string type for the S7StringAttribute")
+                    };
+                    numBytes += sData.Length;
+                    break;
                 default:
-                    var propClass = Activator.CreateInstance(propertyType);
+                    var propClass = Activator.CreateInstance(propertyType) ??
+                        throw new ArgumentException($"Failed to create instance of type {propertyType}.", nameof(propertyType));
+
                     numBytes = FromBytes(propClass, bytes, numBytes);
                     value = propClass;
                     break;
@@ -211,6 +220,8 @@ namespace S7.Net.Types
         /// </summary>
         /// <param name="sourceClass">The object to fill in the given array of bytes</param>
         /// <param name="bytes">The array of bytes</param>
+        /// <param name="numBytes">The offset for the current field.</param>
+        /// <param name="isInnerClass"><see langword="true" /> if this class is the type of a member of the class to be serialized; otherwise, <see langword="false" />.</param>
         public static double FromBytes(object sourceClass, byte[] bytes, double numBytes = 0, bool isInnerClass = false)
         {
             if (bytes == null)
@@ -221,13 +232,15 @@ namespace S7.Net.Types
             {
                 if (property.PropertyType.IsArray)
                 {
-                    Array array = (Array)property.GetValue(sourceClass, null);
+                    Array array = (Array?) property.GetValue(sourceClass, null) ??
+                        throw new ArgumentException($"Property {property.Name} on sourceClass must be an array instance.", nameof(sourceClass));
+
                     IncrementToEven(ref numBytes);
-                    Type elementType = property.PropertyType.GetElementType();
+                    Type elementType = property.PropertyType.GetElementType()!;
                     for (int i = 0; i < array.Length && numBytes < bytes.Length; i++)
                     {
                         array.SetValue(
-                            GetPropertyValue(elementType, bytes, ref numBytes),
+                            GetPropertyValue(elementType, property, bytes, ref numBytes),
                             i);
                     }
                 }
@@ -235,7 +248,7 @@ namespace S7.Net.Types
                 {
                     property.SetValue(
                         sourceClass,
-                        GetPropertyValue(property.PropertyType, bytes, ref numBytes),
+                        GetPropertyValue(property.PropertyType, property, bytes, ref numBytes),
                         null);
                 }
             }
@@ -243,7 +256,7 @@ namespace S7.Net.Types
             return numBytes;
         }
 
-        private static double SetBytesFromProperty(object propertyValue, byte[] bytes, double numBytes)
+        private static double SetBytesFromProperty(object propertyValue, PropertyInfo? propertyInfo, byte[] bytes, double numBytes)
         {
             int bytePos = 0;
             int bitPos = 0;
@@ -285,6 +298,18 @@ namespace S7.Net.Types
                 case "Double":
                     bytes2 = LReal.ToByteArray((double)propertyValue);
                     break;
+                case "String":
+                    S7StringAttribute? attribute = propertyInfo?.GetCustomAttributes<S7StringAttribute>().SingleOrDefault();
+                    if (attribute == default(S7StringAttribute))
+                        throw new ArgumentException("Please add S7StringAttribute to the string field");
+
+                    bytes2 = attribute.Type switch
+                    {
+                        S7StringType.S7String => S7String.ToByteArray((string)propertyValue, attribute.ReservedLength),
+                        S7StringType.S7WString => S7WString.ToByteArray((string)propertyValue, attribute.ReservedLength),
+                        _ => throw new ArgumentException("Please use a valid string type for the S7StringAttribute")
+                    };
+                    break;
                 default:
                     numBytes = ToBytes(propertyValue, bytes, numBytes);
                     break;
@@ -306,26 +331,30 @@ namespace S7.Net.Types
         /// <summary>
         /// Creates a byte array depending on the struct type.
         /// </summary>
-        /// <param name="sourceClass">The struct object</param>
+        /// <param name="sourceClass">The struct object.</param>
+        /// <param name="bytes">The target byte array.</param>
+        /// <param name="numBytes">The offset for the current field.</param>
         /// <returns>A byte array or null if fails.</returns>
         public static double ToBytes(object sourceClass, byte[] bytes, double numBytes = 0.0)
         {
             var properties = GetAccessableProperties(sourceClass.GetType());
             foreach (var property in properties)
             {
+                var value = property.GetValue(sourceClass, null) ??
+                    throw new ArgumentException($"Property {property.Name} on sourceClass can't be null.", nameof(sourceClass));
+
                 if (property.PropertyType.IsArray)
                 {
-                    Array array = (Array)property.GetValue(sourceClass, null);
+                    Array array = (Array) value;
                     IncrementToEven(ref numBytes);
-                    Type elementType = property.PropertyType.GetElementType();
                     for (int i = 0; i < array.Length && numBytes < bytes.Length; i++)
                     {
-                        numBytes = SetBytesFromProperty(array.GetValue(i), bytes, numBytes);
+                        numBytes = SetBytesFromProperty(array.GetValue(i)!, property, bytes, numBytes);
                     }
                 }
                 else
                 {
-                    numBytes = SetBytesFromProperty(property.GetValue(sourceClass, null), bytes, numBytes);
+                    numBytes = SetBytesFromProperty(value, property, bytes, numBytes);
                 }
             }
             return numBytes;

S7.Net/Types/Date.cs

@@ -0,0 +1,82 @@
+using System;
+using S7.Net.Helper;
+
+namespace S7.Net.Types
+{
+    /// <summary>
+    /// Contains the conversion methods to convert Words from S7 plc to C#.
+    /// </summary>
+    public static class Date
+    {
+        /// <summary>
+        /// Minimum allowed date for the IEC date type
+        /// </summary>
+        public static System.DateTime IecMinDate { get; } = new(year: 1990, month: 01, day: 01);
+        
+        /// <summary>
+        /// Maximum allowed date for the IEC date type
+        /// <remarks>
+        /// Although the spec allows only a max date of 31-12-2168, the PLC IEC date goes up to 06-06-2169 (which is the actual
+        /// WORD max value - 65535) 
+        /// </remarks>
+        /// </summary>
+        public static System.DateTime IecMaxDate { get; } = new(year: 2169, month: 06, day: 06);
+        
+        private static readonly ushort MaxNumberOfDays = (ushort)(IecMaxDate - IecMinDate).TotalDays;
+        
+        /// <summary>
+        /// Converts a word (2 bytes) to IEC date (<see cref="System.DateTime"/>)
+        /// </summary>
+        public static System.DateTime FromByteArray(byte[] bytes)
+        {
+            if (bytes.Length != 2)
+            {
+                throw new ArgumentException("Wrong number of bytes. Bytes array must contain 2 bytes.");
+            }
+
+            var daysSinceDateStart = Word.FromByteArray(bytes);
+            if (daysSinceDateStart > MaxNumberOfDays)
+            {
+                throw new ArgumentException($"Read number exceeded the number of maximum days in the IEC date (read: {daysSinceDateStart}, max: {MaxNumberOfDays})", 
+                    nameof(bytes));
+            }
+            
+            return IecMinDate.AddDays(daysSinceDateStart);
+        }
+
+        /// <summary>
+        /// Converts a <see cref="System.DateTime"/> to word (2 bytes)
+        /// </summary>
+        public static byte[] ToByteArray(System.DateTime dateTime) => Word.ToByteArray(dateTime.GetDaysSinceIecDateStart());
+
+        /// <summary>
+        /// Converts an array of <see cref="System.DateTime"/>s to an array of bytes
+        /// </summary>
+        public static byte[] ToByteArray(System.DateTime[] value)
+        {
+            var arr = new ByteArray();
+            foreach (var date in value)
+                arr.Add(ToByteArray(date));
+            return arr.Array;
+        }
+
+        /// <summary>
+        /// Converts an array of bytes to an array of <see cref="System.DateTime"/>s
+        /// </summary>
+        public static System.DateTime[] ToArray(byte[] bytes)
+        {
+            var values = new System.DateTime[bytes.Length / sizeof(ushort)];
+
+            for (int i = 0; i < values.Length; i++)
+            {
+                values[i] = FromByteArray(
+                    new[]
+                    {
+                        bytes[i], bytes[i + 1]
+                    });
+            }
+
+            return values;
+        }
+    }
+}

S7.Net/Types/DateTime.cs

@@ -141,7 +141,7 @@ namespace S7.Net.Types
         /// Converts an array of <see cref="T:System.DateTime"/> values to a byte array.
         /// </summary>
         /// <param name="dateTimes">The DateTime values to convert.</param>
-        /// <returns>A byte array containing the S7 date time representations of <paramref name="dateTime"/>.</returns>
+        /// <returns>A byte array containing the S7 date time representations of <paramref name="dateTimes"/>.</returns>
         /// <exception cref="ArgumentOutOfRangeException">Thrown when any value of
         ///   <paramref name="dateTimes"/> is before <see cref="P:SpecMinimumDateTime"/>
         ///   or after <see cref="P:SpecMaximumDateTime"/>.</exception>

S7.Net/Types/S7String.cs

@@ -9,6 +9,18 @@ namespace S7.Net.Types
     /// </summary>
     public static class S7String
     {
+        private static Encoding stringEncoding = Encoding.ASCII;
+
+        /// <summary>
+        /// The Encoding used when serializing and deserializing S7String (Encoding.ASCII by default)
+        /// </summary>
+        /// <exception cref="ArgumentNullException">StringEncoding must not be null</exception>
+        public static Encoding StringEncoding
+        {
+            get => stringEncoding;
+            set => stringEncoding = value ?? throw new ArgumentNullException(nameof(StringEncoding));
+        }
+
         /// <summary>
         /// Converts S7 bytes to a string
         /// </summary>
@@ -30,7 +42,7 @@ namespace S7.Net.Types
 
             try
             {
-                return Encoding.ASCII.GetString(bytes, 2, length);
+                return StringEncoding.GetString(bytes, 2, length);
             }
             catch (Exception e)
             {
@@ -38,7 +50,6 @@ namespace S7.Net.Types
                     $"Failed to parse {VarType.S7String} from data. Following fields were read: size: '{size}', actual length: '{length}', total number of bytes (including header): '{bytes.Length}'.",
                     e);
             }
-            
         }
 
         /// <summary>
@@ -47,7 +58,7 @@ namespace S7.Net.Types
         /// <param name="value">The string to convert to byte array.</param>
         /// <param name="reservedLength">The length (in characters) allocated in PLC for the string.</param>
         /// <returns>A <see cref="T:byte[]" /> containing the string header and string value with a maximum length of <paramref name="reservedLength"/> + 2.</returns>
-        public static byte[] ToByteArray(string value, int reservedLength)
+        public static byte[] ToByteArray(string? value, int reservedLength)
         {
             if (value is null)
             {
@@ -56,7 +67,7 @@ namespace S7.Net.Types
 
             if (reservedLength > 254) throw new ArgumentException($"The maximum string length supported is 254.");
 
-            var bytes = Encoding.ASCII.GetBytes(value);
+            var bytes = StringEncoding.GetBytes(value);
             if (bytes.Length > reservedLength) throw new ArgumentException($"The provided string length ({bytes.Length} is larger than the specified reserved length ({reservedLength}).");
 
             var buffer = new byte[2 + reservedLength];

S7.Net/Types/S7StringAttribute.cs

@@ -2,7 +2,7 @@
 
 namespace S7.Net.Types
 {
-    [AttributeUsage(AttributeTargets.Field, AllowMultiple = false)]
+    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Property, AllowMultiple = false)]
     public sealed class S7StringAttribute : Attribute
     {
         private readonly S7StringType type;

S7.Net/Types/S7WString.cs

@@ -48,7 +48,7 @@ namespace S7.Net.Types
         /// <param name="value">The string to convert to byte array.</param>
         /// <param name="reservedLength">The length (in characters) allocated in PLC for the string.</param>
         /// <returns>A <see cref="T:byte[]" /> containing the string header and string value with a maximum length of <paramref name="reservedLength"/> + 4.</returns>
-        public static byte[] ToByteArray(string value, int reservedLength)
+        public static byte[] ToByteArray(string? value, int reservedLength)
         {
             if (value is null)
             {

S7.Net/Types/String.cs

@@ -12,13 +12,15 @@
         /// <param name="reservedLength">The amount of bytes reserved for the <paramref name="value"/> in the PLC.</param>
         public static byte[] ToByteArray(string value, int reservedLength)
         {
-            var length = value?.Length;
-            if (length > reservedLength) length = reservedLength;
             var bytes = new byte[reservedLength];
+            if (value == null) return bytes;
 
-            if (length == null || length == 0) return bytes;
+            var length = value.Length;
+            if (length == 0) return bytes;
 
-            System.Text.Encoding.ASCII.GetBytes(value, 0, length.Value, bytes, 0);
+            if (length > reservedLength) length = reservedLength;
+
+            System.Text.Encoding.ASCII.GetBytes(value, 0, length, bytes, 0);
 
             return bytes;
         }

S7.Net/Types/Struct.cs

@@ -45,6 +45,7 @@ namespace S7.Net.Types
                         break;
                     case "Int32":
                     case "UInt32":
+                    case "TimeSpan":
                         numBytes = Math.Ceiling(numBytes);
                         if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
                             numBytes++;
@@ -98,8 +99,8 @@ namespace S7.Net.Types
             int bytePos = 0;
             int bitPos = 0;
             double numBytes = 0.0;
-            object structValue = Activator.CreateInstance(structType);
-
+            object structValue = Activator.CreateInstance(structType) ??
+                throw new ArgumentException($"Failed to create an instance of the type {structType}.", nameof(structType));
 
             var infos = structValue.GetType()
 #if NETSTANDARD1_3
@@ -215,6 +216,21 @@ namespace S7.Net.Types
 
                         numBytes += sData.Length;
                         break;
+                    case "TimeSpan":
+                        numBytes = Math.Ceiling(numBytes);
+                        if ((numBytes / 2 - Math.Floor(numBytes / 2.0)) > 0)
+                            numBytes++;
+                        
+                        // get the value
+                        info.SetValue(structValue, TimeSpan.FromByteArray(new[] 
+                        {
+                            bytes[(int)numBytes + 0],
+                            bytes[(int)numBytes + 1],
+                            bytes[(int)numBytes + 2],
+                            bytes[(int)numBytes + 3]
+                        }));
+                        numBytes += 4;
+                        break;
                     default:
                         var buffer = new byte[GetStructSize(info.FieldType)];
                         if (buffer.Length == 0)
@@ -254,6 +270,14 @@ namespace S7.Net.Types
 
             foreach (var info in infos)
             {
+                static TValue GetValueOrThrow<TValue>(FieldInfo fi, object structValue) where TValue : struct
+                {
+                    var value = fi.GetValue(structValue) as TValue? ??
+                        throw new ArgumentException($"Failed to convert value of field {fi.Name} of {structValue} to type {typeof(TValue)}");
+
+                    return value;
+                }
+
                 bytes2 = null;
                 switch (info.FieldType.Name)
                 {
@@ -261,7 +285,7 @@ namespace S7.Net.Types
                         // get the value
                         bytePos = (int)Math.Floor(numBytes);
                         bitPos = (int)((numBytes - (double)bytePos) / 0.125);
-                        if ((bool)info.GetValue(structValue))
+                        if (GetValueOrThrow<bool>(info, structValue))
                             bytes[bytePos] |= (byte)Math.Pow(2, bitPos);            // is true
                         else
                             bytes[bytePos] &= (byte)(~(byte)Math.Pow(2, bitPos));   // is false
@@ -270,26 +294,26 @@ namespace S7.Net.Types
                     case "Byte":
                         numBytes = (int)Math.Ceiling(numBytes);
                         bytePos = (int)numBytes;
-                        bytes[bytePos] = (byte)info.GetValue(structValue);
+                        bytes[bytePos] = GetValueOrThrow<byte>(info, structValue);
                         numBytes++;
                         break;
                     case "Int16":
-                        bytes2 = Int.ToByteArray((Int16)info.GetValue(structValue));
+                        bytes2 = Int.ToByteArray(GetValueOrThrow<short>(info, structValue));
                         break;
                     case "UInt16":
-                        bytes2 = Word.ToByteArray((UInt16)info.GetValue(structValue));
+                        bytes2 = Word.ToByteArray(GetValueOrThrow<ushort>(info, structValue));
                         break;
                     case "Int32":
-                        bytes2 = DInt.ToByteArray((Int32)info.GetValue(structValue));
+                        bytes2 = DInt.ToByteArray(GetValueOrThrow<int>(info, structValue));
                         break;
                     case "UInt32":
-                        bytes2 = DWord.ToByteArray((UInt32)info.GetValue(structValue));
+                        bytes2 = DWord.ToByteArray(GetValueOrThrow<uint>(info, structValue));
                         break;
                     case "Single":
-                        bytes2 = Real.ToByteArray((float)info.GetValue(structValue));
+                        bytes2 = Real.ToByteArray(GetValueOrThrow<float>(info, structValue));
                         break;
                     case "Double":
-                        bytes2 = LReal.ToByteArray((double)info.GetValue(structValue));
+                        bytes2 = LReal.ToByteArray(GetValueOrThrow<double>(info, structValue));
                         break;
                     case "String":
                         S7StringAttribute? attribute = info.GetCustomAttributes<S7StringAttribute>().SingleOrDefault();
@@ -298,11 +322,14 @@ namespace S7.Net.Types
 
                         bytes2 = attribute.Type switch
                         {
-                            S7StringType.S7String => S7String.ToByteArray((string)info.GetValue(structValue), attribute.ReservedLength),
-                            S7StringType.S7WString => S7WString.ToByteArray((string)info.GetValue(structValue), attribute.ReservedLength),
+                            S7StringType.S7String => S7String.ToByteArray((string?)info.GetValue(structValue), attribute.ReservedLength),
+                            S7StringType.S7WString => S7WString.ToByteArray((string?)info.GetValue(structValue), attribute.ReservedLength),
                             _ => throw new ArgumentException("Please use a valid string type for the S7StringAttribute")
                         };
                         break;
+                    case "TimeSpan":
+                        bytes2 = TimeSpan.ToByteArray((System.TimeSpan)info.GetValue(structValue));
+                        break;
                 }
                 if (bytes2 != null)
                 {

S7.Net/Types/TimeSpan.cs

@@ -0,0 +1,97 @@
+using System;
+using System.Collections.Generic;
+
+namespace S7.Net.Types
+{
+    /// <summary>
+    /// Contains the methods to convert between <see cref="T:System.TimeSpan"/> and S7 representation of TIME values.
+    /// </summary>
+    public static class TimeSpan
+    {
+        /// <summary>
+        /// The minimum <see cref="T:System.TimeSpan"/> value supported by the specification.
+        /// </summary>
+        public static readonly System.TimeSpan SpecMinimumTimeSpan = System.TimeSpan.FromMilliseconds(int.MinValue);
+
+        /// <summary>
+        /// The maximum <see cref="T:System.TimeSpan"/> value supported by the specification.
+        /// </summary>
+        public static readonly System.TimeSpan SpecMaximumTimeSpan = System.TimeSpan.FromMilliseconds(int.MaxValue);
+
+        /// <summary>
+        /// Parses a <see cref="T:System.TimeSpan"/> value from bytes.
+        /// </summary>
+        /// <param name="bytes">Input bytes read from PLC.</param>
+        /// <returns>A <see cref="T:System.TimeSpan"/> object representing the value read from PLC.</returns>
+        /// <exception cref="ArgumentOutOfRangeException">Thrown when the length of
+        ///   <paramref name="bytes"/> is not 4 or any value in <paramref name="bytes"/>
+        ///   is outside the valid range of values.</exception>
+        public static System.TimeSpan FromByteArray(byte[] bytes)
+        {
+            var milliseconds = DInt.FromByteArray(bytes);
+            return System.TimeSpan.FromMilliseconds(milliseconds);
+        }
+
+        /// <summary>
+        /// Parses an array of <see cref="T:System.TimeSpan"/> values from bytes.
+        /// </summary>
+        /// <param name="bytes">Input bytes read from PLC.</param>
+        /// <returns>An array of <see cref="T:System.TimeSpan"/> objects representing the values read from PLC.</returns>
+        /// <exception cref="ArgumentOutOfRangeException">Thrown when the length of
+        ///   <paramref name="bytes"/> is not a multiple of 4 or any value in
+        ///   <paramref name="bytes"/> is outside the valid range of values.</exception>
+        public static System.TimeSpan[] ToArray(byte[] bytes)
+        {
+            const int singleTimeSpanLength = 4;
+            
+            if (bytes.Length % singleTimeSpanLength != 0)
+                throw new ArgumentOutOfRangeException(nameof(bytes), bytes.Length,
+                    $"Parsing an array of {nameof(System.TimeSpan)} requires a multiple of {singleTimeSpanLength} bytes of input data, input data is '{bytes.Length}' long.");
+
+            var result = new System.TimeSpan[bytes.Length / singleTimeSpanLength];
+
+            var milliseconds = DInt.ToArray(bytes);
+            for (var i = 0; i < milliseconds.Length; i++)
+                result[i] = System.TimeSpan.FromMilliseconds(milliseconds[i]);
+
+            return result;
+        }
+
+        /// <summary>
+        /// Converts a <see cref="T:System.TimeSpan"/> value to a byte array.
+        /// </summary>
+        /// <param name="timeSpan">The TimeSpan value to convert.</param>
+        /// <returns>A byte array containing the S7 date time representation of <paramref name="timeSpan"/>.</returns>
+        /// <exception cref="ArgumentOutOfRangeException">Thrown when the value of
+        ///   <paramref name="timeSpan"/> is before <see cref="P:SpecMinimumTimeSpan"/>
+        ///   or after <see cref="P:SpecMaximumTimeSpan"/>.</exception>
+        public static byte[] ToByteArray(System.TimeSpan timeSpan)
+        {
+            if (timeSpan < SpecMinimumTimeSpan)
+                throw new ArgumentOutOfRangeException(nameof(timeSpan), timeSpan,
+                    $"Time span '{timeSpan}' is before the minimum '{SpecMinimumTimeSpan}' supported in S7 time representation.");
+
+            if (timeSpan > SpecMaximumTimeSpan)
+                throw new ArgumentOutOfRangeException(nameof(timeSpan), timeSpan,
+                    $"Time span '{timeSpan}' is after the maximum '{SpecMaximumTimeSpan}' supported in S7 time representation.");
+
+            return DInt.ToByteArray(Convert.ToInt32(timeSpan.TotalMilliseconds));
+        }
+
+        /// <summary>
+        /// Converts an array of <see cref="T:System.TimeSpan"/> values to a byte array.
+        /// </summary>
+        /// <param name="timeSpans">The TimeSpan values to convert.</param>
+        /// <returns>A byte array containing the S7 date time representations of <paramref name="timeSpans"/>.</returns>
+        /// <exception cref="ArgumentOutOfRangeException">Thrown when any value of
+        ///   <paramref name="timeSpans"/> is before <see cref="P:SpecMinimumTimeSpan"/>
+        ///   or after <see cref="P:SpecMaximumTimeSpan"/>.</exception>
+        public static byte[] ToByteArray(System.TimeSpan[] timeSpans)
+        {
+            var bytes = new List<byte>(timeSpans.Length * 4);
+            foreach (var timeSpan in timeSpans) bytes.AddRange(ToByteArray(timeSpan));
+
+            return bytes.ToArray();
+        }
+    }
+}

S7.sln

@@ -9,6 +9,7 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution
 	ProjectSection(SolutionItems) = preProject
 		appveyor.yml = appveyor.yml
 		README.md = README.md
+		.github\workflows\test.yml = .github\workflows\test.yml
 	EndProjectSection
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "S7.Net.UnitTest", "S7.Net.UnitTest\S7.Net.UnitTest.csproj", "{303CCED6-9ABC-4899-A509-743341AAA804}"

appveyor.yml

@@ -1,13 +0,0 @@
-image: Visual Studio 2019
-configuration: Release
-install:
-  - choco install gitversion.portable -y
-before_build:
-  - cmd: gitversion /l console /output buildserver
-  - dotnet restore
-build_script:
-  msbuild /nologo /v:m /p:AssemblyVersion=%GitVersion_AssemblySemVer% /p:FileVersion=%GitVersion_MajorMinorPatch% /p:InformationalVersion=%GitVersion_InformationalVersion% /p:Configuration=%CONFIGURATION% S7.sln
-after_build:
-  - dotnet pack S7.Net -c %CONFIGURATION% /p:Version=%GitVersion_NuGetVersion% --no-build -o artifacts
-artifacts:
-  - path: artifacts\*.*