GE 90-30 to Series 6 CCM Com

I have an application were I am gathering data from a Series 6
via a 90-30 PCM module using RS-422 CCM protocol. The Series 6
has an IOCCM module in it with a Panelmate connected to port 1.
When I connect the PCM to port 2 I get communications errors on both ports. If either the Panelmate or the PCM are connected by themself, communications works fine. Does anybody have any advice on how to correct this problem.

Thankyou

What baud rate are you trying to use? You may need to slow it down when you're trying to use both ports.

19.2k Baud

Back when the 90-30 first came out, there was an advisory from GE Fanuc against trying to communicate at 19.2 kbaud when using both ports of the CMM311 at the same time. They suggested no faster than 9600 baud. Similar limits probably apply to the Series Six IOCCM module. Try reducing your baud rate to 9600 on both ports. If you still get faults, try going to 4800 baud. If reducing the baud rate reduces the frequency of the faults, you'll know you're on the right track.

Also, in the Series Six ladder logic, check the DPREQ or WINDOW instruction that controls the communication between the PLC CPU and the IOCCM module. That could be unconditional (executed every scan) or timed. If it is timed, have it executed more frequently. Most people make this unconditional, but it's worth checking just to make sure.

The Series 6 always prefers to talk the same speed on both ports,
and works best at 2400 or 9600 baud.