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PORS232 connection from PC to PLC slower than using USB2RS232 cable?
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copied!<p>I had a PC connected to a PLC (Mitsubishi Q Series) via a USB2RS232 cable. The cable was plugged into the PC side, which was then plugged into a Serial cable and then into the PLC. I hade the baud rate set to 19200 and everything worked fine. My problem was that every now and then the PC would blue screen on me. When I checked through the dump files the problem seemed to be related to the driver for the USB2RS232 cable (ftdi). I update to the latest driver but still bluescreening (Pc was running Windows 7).</p> <p>Anyway I replaced the PC with another which had a dedicated RS232 port. Now I keep getting communication issues which is indicated by the response by the PLC. Just by chance I lowered the baud rate down to 9600 on both the PC and PLC. The issue seems to have gone away.</p> <p>My question is why would removing the USB2RS232 cable cause me to have to slow down the communication? Both devices can communicate at speeds greater than 19200 and I would have thought going from serial port (PC) to serial port (PLC) with a serial cable would be better.</p> <p>EDIT: Problem maybe solved - still testing</p> <p>Thanks to some of the input from you guys, I may have solved the problem. Here are the following points I went by to get the speed back up to 19200 when using straight RS232 to RS232.</p> <ul> <li>Even though no noise was detected on the equipment, a shielded cable was used.</li> <li>The PC program would wait 100ms between sending data to the PLC. I read somewehere that 100ms is a good approx for PLC scan time.</li> </ul>

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