Accessing the Web-IO Digital with
Visual Basic.Net using
binary sockets

Combining the various operating elements and display objects in the VB.net form

In addition to the objects shown here, the program also needs a timer for polling (timer_polling).

When naming the individual objects it is helpful to use logical names. In this example the first part of the name describes the type of object and the second part the function.

Basics

While constructing graphical user interfaces in Visual Basic Express is just as simple to accomplish as with the previous versions, other tasks may at first take some getting used to.

The Winsock control element familiar from VB5 and VB6 is no longer available for VB in the current version.

Instead, network access requires that the Import statement be used in the header of the source text to instance the namespace for the socket classes used. In addition, the socket over which you want communication to be handled must be created and you must define a buffer for the input data.

Furthermore, encapsulation of individual objects in VB.Net was advanced so far that objects which are created within a thread do not permit access from another thread. For example, a checkbox which was created in Thread A cannot be set from Thread B.

To still make object properties accessible for other threads, sub-procedures for object changing need to be created in a separate thread. Delegates are then formed for these sub-procedures through which the other threads can access.

For example in order to enable control elements in the form after successfully opening a connection or to block them after the connection is closed, but also in order to adjust the input/output checkboxes to the actual I/O states after data is received.

							
Imports System.Net.Sockets
Imports System.Net

Public Class Form1
  Public Structure IO_State
    Dim outputstate0 As Boolean
    Dim outputstate1 As Boolean
    Dim inputstate0 As Boolean
    Dim inputstate1 As Boolean
    Dim countervalue0 As Long
    Dim countervalue1 As Long
  End Structure

  Private Delegate Sub DelegateSub()
  Private connectenable As New DelegateSub(AddressOf connect_enable)
  Private disconnectenable As New DelegateSub(AddressOf disconnect_enable)
  Private formupdate As New DelegateSub(AddressOf form_update)
  Dim TCP_client As Socket
  Dim connection_ar As IAsyncResult
  Dim receivebuffer(511) As Byte
  Dim IOState As IO_State

  Private Sub connect_enable()
    bt_connect.Enabled = False
    gb_io.Enabled = True
    bt_disconnect.Enabled = True
    Timer_polling.Enabled = True
    ToolStripStatusLabel1.Text = "Connected to " + tb_ip.Text + " : " + tb_port.Text
  End Sub

  Private Sub disconnect_enable()
    bt_connect.Enabled = True
    gb_io.Enabled = False
    bt_disconnect.Enabled = False
    timer_polling.Enabled = False
    ToolStripStatusLabel1.Text = "No Connection"
  End Sub

  Private Sub form_update()
    If IOState.inputstate0 = True Then
      cb_input0.Checked = True
    Else
      cb_input0.Checked = False
    End If
    If IOState.inputstate1 = True Then
      cb_input1.Checked = True
    Else
      cb_input1.Checked = False
    End If
    If IOState.outputstate0 = True Then
      cb_output0.Checked = True
    Else
      cb_output0.Checked = False
    End If
    If IOState.outputstate1 = True Then
      cb_Output1.Checked = True
    Else
      cb_Output1.Checked = False
    End If
    tb_counter0.Text = IOState.countervalue0
    tb_counter1.Text = IOState.countervalue1
  End Sub
							
						

The binary structures

For binary access the necessary binary structures used for communicating with the Web-IO must be defined. A detailed description of these structures can be found in the binary brief overview or in the programming manual for the Web-IO.

The IODriver structure
With its four 16-bit variables IODriver is the basic structure which is also part of all other structures.

							
Public Structure structEADriver
  Dim Start_1 As UInt16
  Dim Start_2 As UInt16
  Dim StructType As UInt16
  Dim StructLength As UInt16
End Structure

<StructLayout(LayoutKind.Explicit)> Public Structure structOptions
  <FieldOffset(0)> Dim EADriver As structEADriver
  <FieldOffset(8)> Dim Version As UInt32
  <FieldOffset(12)> Dim Options As UInt32
End Structure

Public Structure structSetBit
  Dim EADriver As structEADriver
  Dim Mask As UInt16
  Dim Value As UInt16
End Structure

Public Structure structReadCounter
  Dim EADriver As structEADriver
  Dim CounterIndex As UInt16
End Structure

Public Structure structWriteRegister
  Dim EADriver As structEADriver
  Dim Amount As UInt16
  Dim Value As UInt16
End Structure

Public Structure structRegisterState
  Dim EADriver As structEADriver
  Dim DriverID As UInt16
  Dim InputValue As UInt16
  Dim OutputValue As UInt16
End Structure

<StructLayout(LayoutKind.Explicit)> Public Structure structCounter
  <FieldOffset(0)> Dim EADriver As structEADriver
  <FieldOffset(8)> Dim CounterIndex As UInt16
  <FieldOffset(10)> Dim CounterValue As UInt32
End Structure

<StructLayout(LayoutKind.Explicit)> Public Structure structAllCounter
  <FieldOffset(0)> Dim EADriver As structEADriver
  <FieldOffset(8)> Dim CounterNoOf As UInt16
  <FieldOffset(10)> Dim CounterValue0 As UInt32
  <FieldOffset(14)> Dim CounterValue1 As UInt32
End Structure
							
						

For the structures it is important that the individual variables be stored in memory in their exact sequence. Visual Basic does not automatic handle this, especially when variables of different sizes are combined in a structure. To still ensure ordered storage in memory, <StructLayout(LayoutKind.Explicit)> is used to specify that each individual variable uses <FieldOffset(14)> to have a fixed offset to the first memory location of the structure assigned.

Connection control

The connection is opened by entering the IP address of the Web-IO in the text field ed_ip and clicking on the bt_connect button.

							
  Private Sub bt_connect_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bt_connect.Click
    Dim WebIOep As New IPEndPoint(IPAddress.Parse(tb_ip.Text), Val(tb_port.Text))
    If tb_ip.Text <> "" And tb_port.Text <> "" Then
      TCP_client = New Socket(AddressFamily.InterNetwork, SocketType.Stream, _ ProtocolType.Tcp)
      bt_connect.Enabled = False
      Try
        TCP_client.BeginConnect(WebIOep, New AsyncCallback(AddressOf callback_connect), TCP_client)
      Catch ex As Exception
      End Try
    End If
  End Sub
							
						

For TCP/IP handling first an IPEndPoint is defined from IP address and TCP port and used to initialize the TCP_client socket. As part of the connection request a reference to a callback procedure is created.

As soon as the Web-IO accepts the connection, the callback procedure is run. An invoke is used to invoke the delegate for the procedure, which enables the control elements and displays the connect status in the status line. In addition a reference to a callback routine for data reception is created.

By sending the structure Options to the Web-IO, the latter is instructed to send the changed state when an output is set, using the structure RegisterState.

							
Private Sub callback_connect(ByVal ar As IAsyncResult)
  Invoke(connectenable)
  connection_ar = ar
  Try
    TCP_client.EndConnect(ar)
    TCP_client.BeginReceive(receivebuffer, 0, 512, SocketFlags.None, New AsyncCallback(AddressOf callback_readdata), TCP_client)
    Dim BufPtr As IntPtr
    Dim Options As structOptions
    Options.EADriver.Start_1 = 0
    Options.EADriver.Start_2 = 0
    Options.EADriver.StructType = &H1F0
    Options.EADriver.StructLength = 16
    Options.Version = 1
    Options.Options = 1
    BufPtr = Marshal.AllocHGlobal(Runtime.InteropServices.Marshal.SizeOf(Options))
    Marshal.StructureToPtr(Options, BufPtr, True)
    sendstructure(BufPtr, Options.EADriver.StructLength)
  Catch ex As Exception
    closeconnections()
  End Try
End Sub
							
						

The connection remains open until it is ended by the user clicking on the Disconnecting button or by the Web-IO.

							  Private Sub bt_disconnect_Click(ByVal sender	As System.Object, ByVal e As System.EventArgs) Handles bt_disconnect.Click
    Invoke(disconnectenable)
    closeconnections()
  End Sub
							
						

In this case a corresponding procedure is invoked.

							  Private Sub closeconnections()
    Try
      TCP_client.EndReceive(connection_ar)
    Catch ex As Exception
    End Try
    Try
      TCP_client.Shutdown(SocketShutdown.Both)
    Catch ex As Exception
    End Try
    Try
      TCP_client.Close()
    Catch ex As Exception
    End Try
    Invoke(disconnectenable)
  End Sub
							
						

All actions affecting TCP/IP communication are executed within the Try instruction. If errors occur, the CloseConnection procedure is also called.

Operation and communication from the client side

As soon as a connection is made with the Web-IO, the user can use the corresponding program elements to send binary structures to the Web-IO.

							
Private Sub sendstructure(ByVal BufPtr As IntPtr, Bufsize As Integer)
  Dim senddata As Byte()
  ReDim senddata(Bufsize - 1)
  Marshal.Copy(BufPtr, senddata, 0, Bufsize)
  Try
    TCP_client.Send(senddata)
  Catch ex As Exception
    closeconnections()
  End Try
  Marshal.FreeHGlobal(BufPtr)
End Sub
							
						

Visual Basic does not provide a method for direct sending of binary structures. Binary data can only be sent as a byte array. Therefore when the sendstructure function is called a pointer is sent. This point references the memory location starting at which the contents of the structure to be sent can be found. Here it is apparent why the structure variables must be in sequence in memory. The second parameter sent is the length of the structure.

Using Marshal.Copy(BufPtr, senddata, 0, Bufsize) the structure data are then copied to a byte array. This byte array is then sent to the Web-IO.

The user sets the outputs by using the two check boxes cb_outputx. For this the program uses the MouseUP event of this object. If a MouseUP, i.e. releasing the output checkbox is registered, the program runs the corresponding procedure and passes the correspondingly filled in Set-Bit structure to the Web-IO.

							
Private Sub cb_output0_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles cb_output0.MouseUp
  Dim BufPtr As IntPtr
  Dim SetBit As structSetBit
  SetBit.EADriver.Start_1 = 0
  SetBit.EADriver.Start_2 = 0
  SetBit.EADriver.StructType = 9
  SetBit.EADriver.StructLength = 12
  SetBit.Mask = 1
  If cb_output0.Checked Then
    SetBit.Value = 1
  Else
    SetBit.Value = 0
  End If
  BufPtr = Marshal.AllocHGlobal(Runtime.InteropServices.Marshal.SizeOf(SetBit))
  Marshal.StructureToPtr(SetBit, BufPtr, True)
  sendstructure(BufPtr, SetBit.EADriver.StructLength)
End Sub

Private Sub cb_Output1_MouseUp(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles cb_Output1.MouseUp
  Dim BufPtr As IntPtr
  Dim SetBit As structSetBit
  SetBit.EADriver.Start_1 = 0
  SetBit.EADriver.Start_2 = 0
  SetBit.EADriver.StructType = 9
  SetBit.EADriver.StructLength = 12
  SetBit.Mask = 2
  If cb_Output1.Checked Then
    SetBit.Value = 2
  Else
    SetBit.Value = 0
  End If
  BufPtr = Marshal.AllocHGlobal(Runtime.InteropServices.Marshal.SizeOf(SetBit))
  Marshal.StructureToPtr(SetBit, BufPtr, True)
  sendstructure(BufPtr, SetBit.EADriver.StructLength)
End Sub
							
						

The user can request the status of the outputs and inputs by clicking on the corresponding button.

							
  Private Sub bt_outputs_read_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bt_outputs_read.Click
    Dim BufPtr As IntPtr
    Dim RegisterRequest As structEADriver
    RegisterRequest.Start_1 = 0
    RegisterRequest.Start_2 = 0
    RegisterRequest.StructType = &H21
    RegisterRequest.StructLength = 8
    BufPtr = Marshal.AllocHGlobal(Runtime.InteropServices.Marshal.SizeOf(RegisterRequest))
    Marshal.StructureToPtr(RegisterRequest, BufPtr, True)
    sendstructure(BufPtr, RegisterRequest.StructLength)
  End Sub
							
						

By sending the structure RegisterRequest the switching states of inputs and outputs are requested. The Web-IO replies to this request with the structure RegisterState.

To query only the inputs, click on the bt_inputs button. Here the structure ReadRegister is sent, to which the Web-IO replies with the structure WriteRegister.

							
  Private Sub bt_inputs_read_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bt_inputs_read.Click
    Dim BufPtr As IntPtr
    Dim ReadRegister As structEADriver
    ReadRegister.Start_1 = 0
    ReadRegister.Start_2 = 0
    ReadRegister.StructType = 1
    ReadRegister.StructLength = 8
    BufPtr = Marshal.AllocHGlobal(Runtime.InteropServices.Marshal.SizeOf(ReadRegister))
    Marshal.StructureToPtr(ReadRegister, BufPtr, True)
    sendstructure(BufPtr, ReadRegister.StructLength)
  End Sub
							
						

You can also query or clear the counter states of the input counters. Here the structure ReadCounter or ReadClearCounter is sent, whereby CounterIndex is used to send the number of the counter. The Web-IO replies with the structure Counter.

							
  Private Sub bt_counter_read0_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bt_counter_read0.Click
    Dim BufPtr As IntPtr
    Dim ReadCounter As structReadCounter
    ReadCounter.EADriver.Start_1 = 0
    ReadCounter.EADriver.Start_2 = 0
    ReadCounter.EADriver.StructType = &HB0
    ReadCounter.EADriver.StructLength = 10
    ReadCounter.CounterIndex = 0
    BufPtr = Marshal.AllocHGlobal(Runtime.InteropServices.Marshal.SizeOf(ReadCounter))
    Marshal.StructureToPtr(ReadCounter, BufPtr, True)
    sendstructure(BufPtr, ReadCounter.EADriver.StructLength)
  End Sub

  Private Sub bt_counter_read1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bt_counter_read0.Click
    Dim BufPtr As IntPtr
    Dim ReadCounter As structReadCounter
    ReadCounter.EADriver.Start_1 = 0
    ReadCounter.EADriver.Start_2 = 0
    ReadCounter.EADriver.StructType = &HB0
    ReadCounter.EADriver.StructLength = 10
    ReadCounter.CounterIndex = 1
    BufPtr = Marshal.AllocHGlobal(Runtime.InteropServices.Marshal.SizeOf(ReadCounter))
    Marshal.StructureToPtr(ReadCounter, BufPtr, True)
    sendstructure(BufPtr, ReadCounter.EADriver.StructLength)
  End Sub

  Private Sub bt_counter_clear0_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bt_counter_clear0.Click
    Dim BufPtr As IntPtr
    Dim ReadClearCounter As structReadCounter
    ReadClearCounter.EADriver.Start_1 = 0
    ReadClearCounter.EADriver.Start_2 = 0
    ReadClearCounter.EADriver.StructType = &HC0
    ReadClearCounter.EADriver.StructLength = 10
    ReadClearCounter.CounterIndex = 0
    BufPtr = Marshal.AllocHGlobal(Runtime.InteropServices.Marshal.SizeOf(ReadClearCounter))
    Marshal.StructureToPtr(ReadClearCounter, BufPtr, True)
    sendstructure(BufPtr, ReadClearCounter.EADriver.StructLength)
  End Sub

  Private Sub bt_counter_clear1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bt_counter_clear0.Click
    Dim BufPtr As IntPtr
    Dim ReadClearCounter As structReadCounter
    ReadClearCounter.EADriver.Start_1 = 0
    ReadClearCounter.EADriver.Start_2 = 0
    ReadClearCounter.EADriver.StructType = &HC0
    ReadClearCounter.EADriver.StructLength = 10
    ReadClearCounter.CounterIndex = 1
    BufPtr = Marshal.AllocHGlobal(Runtime.InteropServices.Marshal.SizeOf(ReadClearCounter))
    Marshal.StructureToPtr(ReadClearCounter, BufPtr, True)
    sendstructure(BufPtr, ReadClearCounter.EADriver.StructLength)
  End Sub
							
						

The structure type RegisterState ReadAllCounter or ReadAllCounter can be used to read or clear all the counters at the same time. The Web-IO replies with the structure AllCounter.

							
  Private Sub bt_counter_readall_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bt_counter_readall.Click
    Dim BufPtr As IntPtr
    Dim ReadAllCounter As structEADriver
    ReadAllCounter.Start_1 = 0
    ReadallCounter.Start_2 = 0
    ReadAllCounter.StructType = &HB1
    ReadAllCounter.StructLength = 10
    BufPtr = Marshal.AllocHGlobal(Runtime.InteropServices.Marshal.SizeOf(ReadAllCounter))
    Marshal.StructureToPtr(ReadAllCounter, BufPtr, True)
    sendstructure(BufPtr, ReadAllCounter.StructLength)
  End Sub

  Private Sub bt_counter_clearall_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles bt_counter_clearall.Click
    Dim BufPtr As IntPtr
    Dim ReadClaerAllCounter As structEADriver
    ReadClaerAllCounter.Start_1 = 0
    ReadClaerAllCounter.Start_2 = 0
    ReadClaerAllCounter.StructType = &HC1
    ReadClaerAllCounter.StructLength = 10
    BufPtr = Marshal.AllocHGlobal(Runtime.InteropServices.Marshal.SizeOf(ReadClaerAllCounter))
    Marshal.StructureToPtr(ReadClaerAllCounter, BufPtr, True)
    sendstructure(BufPtr, ReadClaerAllCounter.StructLength)
  End Sub
							
						

Receiving data from the Web-IO

The Web-IO returns the appropriate structure depending on the query or triggering event. When data are received the corresponding callback procedure is invoked. Processing involves filling the first 8 bytes of the received byte array using a pointer operation first with an IODriver structure. The application recognizes which structure type it is using the variable IODriver.StructType.

• IODriver.StructType = 8
  structure WriteRegister for the status of the inputs
  
  
• IODriver.StructType = 31 (hex)
  structure RegisterState for the status of the inputs and outputs
  
  
• IODriver.StructType = B4 (hex)
  structure Counter for the value of individual counters
  
  
• IODriver.StructType = B5 (hex)
  structure AllCounter for the value of all counters
  
  

For processing the received byte array now uses a pointer operation to fill the appropriate structure.

The values thus sent are then processed and displayed. For the inputs and outputs WriteRegisterValue, RegisterStae.InputValue and RegisterStae.outputValue are used to send the bit pattern of all inputs and outputs.

							
Private Sub callback_readdata(ByVal ar As IAsyncResult)
  If TCP_client.Connected Then
    Dim bytesread As Integer
    Try
      bytesread = TCP_client.EndReceive(ar)
    Catch ex As Exception
    End Try
    If bytesread = 0 Then
      closeconnections()
    Else
      Try
        TCP_client.BeginReceive(receivebuffer, 0, 512, SocketFlags.None, New AsyncCallback(AddressOf callback_readdata), TCP_client)
      Catch ex As Exception
        closeconnections()
      End Try
      Dim MyGC As GCHandle = GCHandle.Alloc(receivebuffer, GCHandleType.Pinned)
      Dim EADriver As structEADriver = Marshal.PtrToStructure(MyGC.AddrOfPinnedObject, EADriver.GetType)

      Select Case EADriver.StructType
      Case 8
        Dim WriteRegister As structWriteRegister = Marshal.PtrToStructure(MyGC.AddrOfPinnedObject, WriteRegister.GetType)
        If (WriteRegister.Value And 1) = 1 Then
          IOState.inputstate0 = True
        Else
          IOState.inputstate0 = False
        End If
        If (WriteRegister.Value And 2) = 2 Then
          IOState.inputstate1 = True
        Else
          IOState.inputstate1 = False
        End If
      Case &H31
        Dim RegisterState As structRegisterState = Marshal.PtrToStructure(MyGC.AddrOfPinnedObject, RegisterState.GetType)
        If (RegisterState.InputValue And 1) = 1 Then
          IOState.inputstate0 = True
        Else
          IOState.inputstate0 = False
        End If
        If (RegisterState.InputValue And 2) = 2 Then
          IOState.inputstate1 = True
        Else
          IOState.inputstate1 = False
        End If
        If (RegisterState.OutputValue And 1) = 1 Then
          IOState.outputstate0 = True
        Else
          IOState.outputstate0 = False
        End If
        If (RegisterState.OutputValue And 2) = 2 Then
          IOState.outputstate1 = True
        Else
          IOState.outputstate1 = False
        End If
      Case &HB4
        Dim Counter As structCounter = Marshal.PtrToStructure(MyGC.AddrOfPinnedObject, Counter.GetType)
        If Counter.CounterIndex = 0 Then IOState.countervalue0 = Counter.CounterValue.ToString
        If Counter.CounterIndex = 1 Then IOState.countervalue1 = Counter.CounterValue.ToString
      Case &HB5
        Dim AllCounter As structAllCounter = Marshal.PtrToStructure(MyGC.AddrOfPinnedObject, AllCounter.GetType)
        IOState.countervalue0 = AllCounter.CounterValue0.ToString
        IOState.countervalue1 = AllCounter.CounterValue1.ToString
      End Select
      Invoke(formupdate)
      MyGC.Free()
    End If
  End If
End Sub
							
						

Polling

In order to enable automatic refreshing of the display, a timer is used.

Depending on the check boxes for output, input and counter polling, the corresponding information is obtained from the Web-IO at a set interval.

							
  Private Sub timer_polling_Elapsed(ByVal sender As System.Object, ByVal e As System.Timers.ElapsedEventArgs) Handles timer_polling.Elapsed
    If ((cb_input_polling.Checked Or cb_output_polling.Checked) And TCP_client.Connected) Then
      Dim BufPtr As IntPtr
      Dim RegisterRequest As structEADriver
      RegisterRequest.Start_1 = 0
      RegisterRequest.Start_2 = 0
      RegisterRequest.StructType = 1
      RegisterRequest.StructLength = &H21
      BufPtr = Marshal.AllocHGlobal(Runtime.InteropServices.Marshal.SizeOf(RegisterRequest))
      Marshal.StructureToPtr(RegisterRequest, BufPtr, True)
      sendstructure(BufPtr, RegisterRequest.StructLength)
    End If
    If (cb_counter_polling.Checked And TCP_client.Connected) Then
      Dim BufPtr As IntPtr
      Dim ReadAllCounter As structEADriver
      ReadAllCounter.Start_1 = 0
      ReadAllCounter.Start_2 = 0
      ReadAllCounter.StructType = &HB1
      ReadAllCounter.StructLength = 10
      BufPtr = Marshal.AllocHGlobal(Runtime.InteropServices.Marshal.SizeOf(ReadAllCounter))
      Marshal.StructureToPtr(ReadAllCounter, BufPtr, True)
      sendstructure(BufPtr, ReadAllCounter.StructLength)
    End If
  End Sub
							
						

The desired interval can be entered in the corresponding text field. When changes are made the timer interval is automatically adjusted.

							
  Private Sub tb_interval_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles tb_interval.TextChanged
    timer_polling.Interval = Val(tb_interval.Text)
  End Sub