W&T connects
Interfaces for TCP/IP, Ethernet, RS-232, RS-485, USB, 20mA, glass and plastic fiber optic cable, http, SNMP, OPC, Modbus TCP, I/O digital, I/O analog, ISA, PCI

Application for the Web-IO Digital:

Control and monitor Web-IO Digital with VB.Net


VB.net has established itself as the successor to MS Visual Basic. Visual Basic.net offers everything needed for programming TCP/IP applications. This makes Visual Basic.net a favorite tool for creating applications which communicate with the Web-IO Digital. Additional drivers or DLLs are not required.

Control with Visual Basic

Using the following program example you can represent your Web-IO Digital with its inputs and outputs in a Windows application. You can also switch the Web-IO outputs.

Preparations

You have already provided your Web-IO Digital

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

Visual Basic operating elements

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.

1. Starting the program

While the structure of graphical user interfaces in VB.net is just as easy to accomplish as with VB5 or VB6, the network communication under VB.net is somewhat more difficult to construct than with its predecessor. This is primarily because Microsoft no longer provides the Winsock control element with VB.net. Instead, network access requires that the Import Statement be used to instance the namespace for the socket classes used in the header of the source text.

In addition, the socket on which communication will be handled must be created and a buffer for the input data needs to be defined.


				Imports System.Net
				Imports System.Net.Sockets
				Imports System.IO
				Imports System.Windows.Forms
				Public Class Form1
				Inherits System.Windows.Forms.Form
				Dim TCP_client As Socket
				Dim receivebuffer(511) As Byte

2. Connection control

Establishing the connection

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
					closeconnections()
					MessageBox.Show(ex.Message, "Socket Error", MessageBoxButtons.OK, _
					MessageBoxIcon.Error)
					End Try
				End If
				End Sub
		
Opening the connection

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.

Connection is made

As soon as a connection is made with the Web-IO, the callback procedure is run. The status line shows that the connection has been opened, the operating elements are enabled for use and the Disconnect button becomes operable. The Connect button is blocked for operation. In addition a reference to a callback routine for data reception is created.


				Private Sub callback_connect(ByVal ar As IAsyncResult)
				bt_connect.Enabled = False
				gb_io.Enabled = True
				bt_disconnect.Enabled = True
				StatusBar1.Text = "Connected to " + tb_ip.Text + " : " + tb_port.Text
				timer_polling.Enabled = True
				Try
				TCP_client.EndConnect(ar)
				TCP_client.BeginReceive(receivebuffer, 0, 512, SocketFlags.None, New AsyncCallback(AddressOf
				callback_readdata), TCP_client)
				Catch ex As Exception
				closeconnections()
				StatusBar1.Text = "error on connecting"
				End Try
			End Sub
		
Disconnecting

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


				Private Sub bt_disconnect_Click(ByVal sender
			As System.Object, _
			ByVal e As System.EventArgs) Handles bt_disconnect.Click
				bt_disconnect.Enabled = False
				closeconnections()
			End Sub
		

In this case a corresponding procedure is invoked.


				Private Sub closeconnections()
				Dim ar As IAsyncResult
				timer_polling.Enabled = False
				Try
				TCP_client.EndReceive(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
				bt_connect.Enabled = True
				gb_io.Enabled = False
				bt_disconnect.Enabled = False
				StatusBar1.Text = "no connection"
			End Sub
		
Connection error

All the actions affecting TCP/IP communication are carried out within the Try-instruction. If errors occur, the CloseConnection procedure is also invoked.

3. 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 commands to the Web-IO


				Private Sub sendcommand(ByVal sendstring As String)
				Dim senddata As Byte() = System.Text.Encoding.ASCII.GetBytes(sendstring)
				Try
					TCP_client.Send(senddata)
				Catch ex As Exception
					closeconnections()
				End Try
				End Sub
		
Setting the outputs

The user sets the outputs by using the two check boxes cb_outputx. The program uses the MouseUP event of this object. If a Mouse Up, i.e. releasing the output check box, is used, the program carries out the corresponding procedure and - depending on whether the check box is set or not - passes the appropriate command to the Web-IO.


				Private Sub cb_output0_MouseUp(ByVal sender As Object, _
				ByVal e As System.Windows.Forms.MouseEventArgs) Handles cb_output0.MouseUp
				If cb_output0.Checked Then
					sendcommand("GET /outputaccess0?PW="+ tb_password.Text + "&State=ON&")
				Else
					sendcommand("GET /outputaccess0?PW="+ tb_password.Text + "&State=OFF&")
				End If
				End Sub
		

				Private Sub cb_output1_MouseUp(ByVal sender As Object, _
				ByVal e As System.Windows.Forms.MouseEventArgs) Handles cb_output1.MouseUp
				If cb_output1.Checked Then
					sendcommand("GET /outputaccess1?PW="+ tb_password.Text + "&State=ON&")
				Else
					sendcommand("GET /outputaccess1?PW="+ tb_password.Text + "&State=OFF&")
				End If
				End Sub
		
Querying output/input status

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
				sendcommand("GET /output?PW=" + tb_password.Text + "&")
			End Sub
		

				Private Sub bt_inputs_read_Click(ByVal
			sender As System.Object, _
			ByVal e As System.EventArgs) Handles bt_inputs_read.Click
				sendcommand("GET /input?PW=" + tb_password.Text + "&")
			End Sub
		
Read/clear counters

Also the counter states of the input counters can be read or cleared.


				Private Sub bt_counter_read0_Click(ByVal sender As System.Object,
				_
				ByVal e As System.EventArgs) Handles bt_counter_read0.Click
				sendcommand("GET /counter0?PW=" + tb_password.Text + "&")
				End Sub
		

				Private Sub bt_counter_read1_Click(ByVal sender
				As System.Object, _
				ByVal e As System.EventArgs) Handles bt_counter_read0.Click
				sendcommand("GET /counter1?PW=" + tb_password.Text + "&")
				End Sub
		

				Private Sub bt_counter_clear0_Click(ByVal sender As System.Object,
				_
				ByVal e As System.EventArgs) Handles bt_counter_clear0.Click
					sendcommand("GET /counterclear0?PW=" + tb_password.Text + "&")
				End Sub
		

				Private Sub bt_counter_clear1_Click(ByVal
				sender As System.Object, _
				ByVal e As System.EventArgs) Handles bt_counter_clear0.Click
					sendcommand("GET /counterclear1?PW=" + tb_password.Text + "&")
				End Sub
		

Of course all the counters can be read or cleared at the same time.


				Private Sub bt_counter_readall_Click(ByVal
			sender As System.Object, _
			ByVal e As System.EventArgs) Handles bt_counter_readall.Click
				sendcommand("GET /counter?PW=" + tb_password.Text + "&")
			End Sub
		

				Private Sub bt_counter_clearall_Click(ByVal
			sender As System.Object, _
			ByVal e As System.EventArgs) Handles bt_counter_clearall.Click
				sendcommand("GET /counterclear?PW=" + tb_password.Text + "&")
			End Sub
		

3. Data reception from the Web-IO

Process and display the received data
  • All commands and requests to the Web-IO are acknowledged with a reply string. The replies have a specific structure depending on the type.
  • For the outputs: output;<binary value of the output status in hexadecimal format>
  • For the inputs: input;<binary value of the input status in hexadecimal format>
  • For the counters: counterx;<decimal counter state>
  • or counter;<decimal counter state 0 >; <decimal counter state 0 >;.....if you want to read all counters at the same time.
  • All reply strings are finished off with a 0 byte.
  • When data are received the corresponding Callback procedure is invoked

				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
				Dim receivestring As String
				receivestring = System.Text.Encoding.ASCII.GetString(receivebuffer,0, _
				receivebuffer.Length)
				receivebuffer.Clear(receivebuffer, 0, 512)
				Try
					TCP_client.BeginReceive(receivebuffer, 0, 512, SocketFlags.None, New AsyncCallback(AddressOf
			callback_readdata), TCP_client)
				Catch ex As Exception
					closeconnections()
				End Try
				Select Case Mid(receivestring, 1, 1)
					Case "i"
						If (Val(Mid(receivestring, 7, 1)) And 1) = 1 Then
						cb_input0.Checked = True
						Else
						cb_input0.Checked = False
						End If
						If (Val(Mid(receivestring, 7, 1)) And 2) = 2 Then
						cb_input1.Checked = True
						Else
						cb_input1.Checked = False
						End If
					Case "o"
						If (Val(Mid(receivestring, 8, 1)) And 1) = 1 Then
						cb_output0.Checked = True
						Else
						cb_output0.Checked = False
						End If
						If (Val(Mid(receivestring, 8, 1)) And 2) = 2 Then
						cb_output1.Checked = True
						Else
						cb_output1.Checked = False
						End If
					Case "c"
						Dim tabpos
						If Mid(receivestring, 8, 1) = "0" Then _
							tb_counter0.Text = Mid(receivestring, 10)
						If Mid(receivestring, 8, 1) = "1" Then _
							tb_counter1.Text = Mid(receivestring, 10)
						If Mid(receivestring, 8, 1) = ";" Then
							tabpos = InStr(9, receivestring, ";")
							tb_counter0.Text = Mid(receivestring, 9, tabpos - 9)
							tb_counter1.Text = Mid(receivestring, tabpos + 1, _
							Len(receivestring) - tabpos - 1)
						End If
				End Select
				End If
				End If
			End Sub
			

The Receive procedure uses the first character of the receive data to check whether these are input, output or counter messages. Depending on this, a determination is made for example as to which output has which status. With the counters it is possible both to query individual counter values as well as to read out all the counters at one time. The individual counter states are then output in decimal format in a semicolon delimited string.

4. Polling

Cyclical polling of particular values

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 And TCP_client.Connected) Then
					sendcommand("GET /input?PW=" + tb_password.Text + "&")
				End If
				If (cb_output_polling.Checked And TCP_client.Connected) Then
					sendcommand("GET /output?PW=" + tb_password.Text + "&")
				End If
				If (cb_output_polling.Checked And TCP_client.Connected) Then
					sendcommand("GET /output?PW=" + tb_password.Text + "&")
				End If
				If (cb_counter_polling.Checked And TCP_client.Connected) Then
					sendcommand("GET /counter?PW=" + tb_password.Text + "&")
				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
			

The sample program supports all common functions of the Web-IO in command string mode, optimized for the Web-IO 2x Digital Input, 2x Digital Output. For the other Web-IO models you may have to adapt the program. Additional program examples for socket programming can be found on the tool pages for the Web-IO. A detailed description for the socket interface of the Web-IO Digital models can be found in the reference manual.