• Vb Serial Port Example

Posted: 25 Mar 05 (Edited 25 Mar 05) You can use the MSComm control to access COM ports. This will let you read or write data directly to a COM port, much like using HyperTerminal to directly access a port. You can also use this control to control a modem using AT commands. The MSComm control comes with VB6. Add it to your project by going to the Project-Components menu item and adding 'Microsoft Comm Control 6.0' to your project.

You can then select the control in your toolbox and add it to a form. Here is a very basic example of using the MSComm control. This will open COM1, send a string to the port, and get back any response from the attached device.

Please note that if you need to send binary data instead of ANSI text, you will need to assign a Byte array to the.Output property instead of a string. Likewise, if you want to recieve binary data, you will need to set the.InputMode property and assign.Input to a Byte array. Dim s As String With MSComm1 ' First we initialize a few properties. ' Set the COM port number.CommPort = 1 ' The communication settings. The values are: ' baud rate, parity, data bits, stop bits.Settings = '9600,n,8,1' ' Recieve and send thresholds, described below.RThreshold = 1.SThreshold = 1 ' Open COM1 and begin communications.PortOpen = True ' Send the string 'some data' to the output buffer.Output = 'some data' ' Get the current contents of the input buffer. S =.Input End With In addition to the.Settings property, there are a number of other properties that relate to the communication protocol used for the port, such as.Handshaking,.RTSEnable, and.EOFEnable. The correct settings for each property will depend on the device with which you are attempting to communicate.

If you are having trouble getting a device to respond, you should check the documentation for your device and for the MSComm control and make sure that all the control's properties are set correctly. Doing anything interesting with the MSComm control will require using the control's OnComm event. This event will be fired whenever the.CommEvent property of the control changes, which is basically whenever anything interesting happens on the COM port. Which comm events you need to worry about will depend on what you are trying to do. One of the more common events is comEvRecieve, which is triggered when the control recieves data from the attached device.

This is useful when you need to capture a large stream of incoming data. Please note, however, that comEvRecieve is governed by the value of the.RThreshold property, which holds the number of characters that should be recieved before the OnComm event is fired. If.RThreshold is set to zero (the default), then the the OnComm will not be fired for incoming data. The same is true of.SThreshold and the comEvSend event which is fired when data is sent. Here is an example of using the OnComm event in a very simple terminal emulator program.

This program has three button (Dial, HangUp, and SendCmd) and two text boxes (CmdBox and OutputBox). It will use a modem on COM1 to dial some remote system, send it some commands entered by the user, and dump any data it gets back into a text box. (Note: This code has not been tested. It is for educational use only. Error checking and other details have been omitted for clarity). Private Sub Form1Load With MSComm1.CommPort = 1.Settings = '9600,n,8,1'.RTSEnabled = True.RThreshold = 1.Handshaking = comNone End With OutputBox.Multiline = True End Sub ' Dial a hard-coded phone number and wait for ' the modem to connect. Private Sub DialClick With MSComm1 If.PortOpen Then MsgBox 'Port already opened.'

Exit Sub End If.PortOpen = True.Output = '.Output = 'ATDT 5551234' & vbCrLf OutputBox.Text = 'Dialing 555-1234' ' Wait for the carrier detect signal, which ' indicates that the modem is connected. Do Until.CDHolding OutputBox.Text = OutputBox.Text & '.'

DoEvents Loop End With End Sub ' Hang up the modem. Private Sub HangUpClick OutputBox.Text = OutputBox.Text & 'Hanging up.' With MSComm1.Output = '.Output = 'ATH0'.PortOpen = False End With End Sub ' Send the text entered in the command box to the ' remote system, then clear the box. Private Sub SendCmdClick With MSComm1 If.PortOpen Then.Output = CmdBox.Text & vbCrLf CmdBox.Text = vbNullString Else MsgBox 'Port is closed.' End If End With End Sub Private Sub MSComm1OnComm Select Case MSComm1.CommEvent ' Capture any incoming data and write ' it to the output box. Case comEvSend OutputBox.Text = OutputBox.Text & MSComm1.Input ' Capture changes in the carrier detect line.

' This will detect if the modem has been 'disconnected. Case comEvCD If Not MSComm1.CDHolding Then HangUpClick OutputBox.Text = OutputBox.Text & 'Disconnected.'

End If End Select End Sub.

MSComm Control Example The following simple example shows basic serial communications using a modem: Private Sub FormLoad ' Buffer to hold input string Dim Instring As String ' Use COM1. MSComm1.CommPort = 1 ' 9600 baud, no parity, 8 data, and 1 stop bit. MSComm1.Settings = '9600,N,8,1' ' Tell the control to read entire buffer when Input ' is used.

MSComm1.InputLen = 0 ' Open the port. MSComm1.PortOpen = True ' Send the attention command to the modem. MSComm1.Output = 'ATV1Q0' & Chr$(13) ' Ensure that ' the modem responds with 'OK'. ' Wait for data to come back to the serial port. Do DoEvents Buffer$ = Buffer$ & MSComm1.Input Loop Until InStr(Buffer$, 'OK' & vbCRLF) ' Read the 'OK' response data in the serial port.

' Close the serial port. MSComm1.PortOpen = False End Sub Note The MSComm control can use polling or an event-driven method to retrieve data from the port. This simple example uses the polling method. For an example of the event-driven method, see help for the OnComm event. There are loads more examples around here, try using the search feature in the upper right corner. The OnComm event for the MSComm control is what you will be most concerned with. Thank u for reply i am sending the data by this code and getting the data back in the text box but i want that the data which is coming in the textbox is should be loop,it should not be stop until i end my program.

And I am sending this data to robots which they reply data back to me in vb form. And What code u send is correct but it does not show me the vb Form it directly send data to robot by which it walks,but does not display the data in text box.

Vb Serial Port Example

And I dont Know how to use loop to get the data in textbox in a loop That data should be display in consecutive or sequential manner in the Textbox or label control. Private sub Command1click Dim bytetosend(0 To 1) As Byte Dim buffer As Variant bytetosend(0) = &H59 buffer = bytetosend MSComm1.Output = buffer Do dummy = DoEvents Loop Until MSComm1.InBufferCount 5 datain = MSComm1.Input Text2.Text = Hex$(Asc(Mid$(datain, 1, 1))) Label1.caption=Hex$(Asc(Mid$(datain, 1, 1))) Thank u very, much if u read this mail today then please reply me today only if u can and not make it possible then give me a reference from which i can query this. Thank u Thank u Thank u.