Serial Port

I have two computers connected to each other through the serial port with an RS232 cable. I tried with some snippets I found out there, but I cannot make anything going out of the port to the other computer (MSComm1.OutBufferCount is always 0 regardless what I wrote on its Output property). Does anybody have any example I can try? TIA,

Do you have the right cable? It should be "cross-over"

It's the same RS232 cable I've used before to transmit files from one machine to another (using Norton Commander, for example).

Is your firewall blocking it?

Nope, both firewalls are disabled and stil the OutBufferCount remains equals to zero. Any ideas?

Are you using any handshaking (RTS/CTS) in your code?

Actually - can you post some code

On the receiver:

VB Code:

Private Sub Form_Load()
    ' Use COM2.
    MSComm1.CommPort = 2
    ' 9600 baud, no parity, 8 data, and 1 stop bit.
    MSComm1.Settings = "9600,N,8,1"
End Sub
'*************
 
Private Sub MSComm1_OnComm()
    Stop
End Sub

On the sender:

VB Code:

Option Explicit
 
Private Sub Command1_Click()
    Dim sText As Variant
    
    With MSComm1
        .PortOpen = True
        sText = Chr$(Val(txtSend.Text))
        
        .Output = sText
        Do
            DoEvents
        Loop Until .OutBufferCount = 0
        .PortOpen = False
    End With
End Sub
 
Private Sub Form_Load()
    ' Use COM1.
    MSComm1.CommPort = 1
    ' 9600 baud, no parity, 8 data, and 1 stop bit.
    MSComm1.Settings = "9600,N,8,1"
End Sub

Quote:

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Originally Posted by David.Poundall

Are you using any handshaking (RTS/CTS) in your code?

---

No. Handshaking = 0 comNone

The cable is Ok, and the firewall is not blocking since I receive these events on the receiver:

comEvDSR: When I open the port on the sender to send a data out (twice)
comEventBreak: When I close the port after (not) sending the data.

OK - just a couple of points. I am referring to a comprehensive PLC comms routine that I have been successfully running for the past 5 years. But as you may imagine it was written five years ago. Anyway - enough of my problem and on to yours.

Here are a few snippets of my code that works. Unlike yours it works in binary mode though.

My receive code just unloads the Rxbuff array. The data received event fires when I receive the correct number of incoming bytes as PLC comms is quite predictable.

VB Code:

' ---------------------------------------------------------------------
' Globals
Public Rxbuff() As Byte
 
' ---------------------------------------------------------------------
' Code behind the Form containing the comm control
Private Sub MSComm1_OnComm()
     Select Case MSComm1.CommEvent          
          Case comEvReceive         ' Received RThreshold # of chars.
               Rxbuff() = MSComm1.Input
               Call HandleReceivedData              
     End Select
End Sub
 
' ---------------------------------------------------------------------
' called at comms kickoff
Sub InitialiseComms()
     frmPlcComms.MSComm1.CommPort = ComPort
     frmPlcComms.MSComm1.Settings = "9600,E,7,1"
     frmPlcComms.MSComm1.PortOpen = True
     frmPlcComms.MSComm1.DTREnable = True
     frmPlcComms.MSComm1.RTSEnable = True
     frmPlcComms.MSComm1.InputMode = comInputModeBinary
     frmPlcComms.MSComm1.InputLen = 0       'Forces entire buffer read
End Sub
 
' ---------------------------------------------------------------------
' send code
Sub Transmit()
    Dim txbuff() As Byte, k as long
    Dim SendBuffer(1) As Variant                       ' VIP for sending Binary
 
    frmPlcComms.MSComm1.InBufferCount = 0     'Flush the RX Buffer
          
    ' Dim the TX buffer
    redim txbuff(0 to 100)
 
    k = 0
    ' Send pre-amble
    txbuff(k) = &H2   : k = k+1
    txbuff(k) = &H31  : k = k+1
    txbuff(k) = &H31  : k = k+1
 
    ' Add further text to the byte buffer as byte...
 
    ' Trim the TXbuffer
    ReDim txbuff(0 to k-1)
 
    SendBuffer(1) = txbuff()
    frmPlcComms.MSComm1.Output = SendBuffer(1)
 
    ' Set the  RX buffer length to the value expected from the PLC
    frmPlcComms.MSComm1.RThreshold = 1          ' Note - Not typical.
    
End Sub

Something in that lot may jog your thinking.

It seems I made it work.

Hmmm have you tried ....

VB Code:

sText = txtSend.Text

??

Quote:

---

Originally Posted by David.Poundall

OK - just a couple of points. I am referring to a comprehensive PLC comms routine that I have been successfully running for the past 5 years. But as you may imagine it was written five years ago. Anyway - enough of my problem and on to yours.

Here are a few snippets of my code that works. Unlike yours it works in binary mode though.

My receive code just unloads the Rxbuff array. The data received event fires when I receive the correct number of incoming bytes as PLC comms is quite predictable.

VB Code:

' ---------------------------------------------------------------------
' Globals
Public Rxbuff() As Byte
 
' ---------------------------------------------------------------------
' Code behind the Form containing the comm control
Private Sub MSComm1_OnComm()
     Select Case MSComm1.CommEvent          
          Case comEvReceive         ' Received RThreshold # of chars.
               Rxbuff() = MSComm1.Input
               Call HandleReceivedData              
     End Select
End Sub
 
' ---------------------------------------------------------------------
' called at comms kickoff
Sub InitialiseComms()
     frmPlcComms.MSComm1.CommPort = ComPort
     frmPlcComms.MSComm1.Settings = "9600,E,7,1"
     frmPlcComms.MSComm1.PortOpen = True
     frmPlcComms.MSComm1.DTREnable = True
     frmPlcComms.MSComm1.RTSEnable = True
     frmPlcComms.MSComm1.InputMode = comInputModeBinary
     frmPlcComms.MSComm1.InputLen = 0       'Forces entire buffer read
End Sub
 
' ---------------------------------------------------------------------
' send code
Sub Transmit()
    Dim txbuff() As Byte, k as long
    Dim SendBuffer(1) As Variant                       ' VIP for sending Binary
 
    frmPlcComms.MSComm1.InBufferCount = 0     'Flush the RX Buffer
          
    ' Dim the TX buffer
    redim txbuff(0 to 100)
 
    k = 0
    ' Send pre-amble
    txbuff(k) = &H2   : k = k+1
    txbuff(k) = &H31  : k = k+1
    txbuff(k) = &H31  : k = k+1
 
    ' Add further text to the byte buffer as byte...
 
    ' Trim the TXbuffer
    ReDim txbuff(0 to k-1)
 
    SendBuffer(1) = txbuff()
    frmPlcComms.MSComm1.Output = SendBuffer(1)
 
    ' Set the  RX buffer length to the value expected from the PLC
    frmPlcComms.MSComm1.RThreshold = 1          ' Note - Not typical.
    
End Sub

Something in that lot may jog your thinking.

---

Yes, the key was the "RThreshold" and I had found it (almost at the same time you posted it) at http://www.programmers-corner.com/sourcecode/111.

VB Code:

'enable the oncomm event for every reveived character
    .RThreshold = 1

Quote:

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Originally Posted by Mc Brain

It seems I made it work.

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That's good news. How did you do it ?

Cool