Serial Port

[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