Hello,

I've communicated with my device (M3) over Modbus Poll. Standard setting and Modbus ASCII. This worked fine and I tried to write a C++ program which would do the same.

I'm handling the device like a file:<pre>









m_hCom = CreateFile(m_sComPort,
GENERIC_READ | GENERIC_WRITE,
0, // exclusive access
NULL, // no security
OPEN_EXISTING,
0, // no overlapped I/O
NULL); // null template

// This request is exactly the same like the one ModbusPoll sends
char strASCII[] = "3A 30 31 30 33 30 30 30 30 30 30 30 34 46 38 0D 0A";

iBytesWritten = 0;
// Talk to the M3
//WriteFile (m_hCom, str, strlen (str), &iBytesWritten, NULL);

bWriteRC = WriteFile (m_hCom, strASCII, strlen(strASCII), &iBytesWritten, NULL);

memset(sBuffer,0,sizeof(sBuffer));
// Read output of the M3
bReadRC = ReadFile (m_hCom, &sBuffer, sizeof(&sBuffer), &iBytesRead, NULL);

if (bReadRC && iBytesRead > 0)
{
sResult = sBuffer;
}
else
{
sResult = "Read Failed";
dwError = GetLastError();

sprintf(sMsg, "Read length failed: RC=%d Bytes read=%d, "
"Error=%d ",
bReadRC, iBytesRead, dwError);
AfxMessageBox(sMsg);
} // end if</pre>
And you guess it, i get the Read length failed error.
The whole program, my sources are out can be found here http://www.ontrak.net/mfc.htm (Link on the bottom). Simple serial communication.

Can anyone here help me?

Regards
Andreas

 

You did not call the
SetCommConfig function
You may have wrong baud rate, handshake ...

google: msdn commconfig

Here is our Modbus class.
You walk through it's source code
http://tinyurl.com/az4llre

 

Thank you very much, will do.