Serial Port

[Mc Brain]

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,

[zigona]

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

[Mc Brain]

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

[dglienna]

Is your firewall blocking it?

[Mc Brain]

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

[David.Poundall]

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

[David.Poundall]

Actually - can you post some code

[Mc Brain]

On the receiver:

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:

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

[Mc Brain]

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

No. Handshaking = 0 comNone

[Mc Brain]

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.

[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.

' ---------------------------------------------------------------------
' 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.

[Mc Brain]

It seems I made it work.

[David.Poundall]

Hmmm have you tried ....

sText = txtSend.Text

??

[Mc Brain]

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.

' ---------------------------------------------------------------------
' 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.

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

[David.Poundall]

It seems I made it work.

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

[David.Poundall]

Cool