I wrote a serial communications program, named serialComm, in VB6 using the MSCOMM control. serialComm is intended to talk to an external device, call it PLC. The RS232 port is made with a USB/RS232 converter.
My machine is running Windows 7. serialComm works fine on my machine, both from within VB6, and when I run the installed one outside of VB6. But when I sent it to my customer and they installed it on their Win7 machine it does not work. Their machine does not have VB6 installed.
The customer is using the very same USB/RS232 converter and they can communicate with the PLC via Hyperterminal. When they run serialComm, the proper port opens and all looks good but there is simply no response from the PLC.
We checked the RS232 transmit line (pin 3 of the 9-pin D is Tx from the PC) and when the command is sent we get a single 70 micro-second wide pulse. It should be several bit transitions because we are sending about 9 characters. We also checked the receive line to be sure and there was nothing on it, just flat lined.
Not sure if it matters but both machines have .NET v4.0.30319 on them.
Any insight into this problem would be greatly appreciated. Thank you.