GE-PLC Communication Problem

Hi,
I have some problems communicating with the older style GE-Fanuc PLC's. They are the series-90 28 point micro. I am using a Red Lion HMI with them. I was able to communicate and load a program to two of the four PLC's at the site but the other two I was not able to communicate with. The two that i downloaded a new program two work fine with there HMI, but the ones that I was not able to communicate with where not able to communicate with there HMI either, the PLC's are still working with the old program but i would like to revise the program. I looked at the cables and everything looked tight and clean. Any help would be greatly appreciated.

Which port are you using for HMI communications? Are you sure the port is configured for the proper protocol? Have you tried using the other port? The port is RS485. That's why you need the converter for communications with your PC. The converter is powered by the port. Check for +5VDC between pins 5 and 7 on the port.

CG_Kevin sent me the following email:

Hi,
I am using the programming port for the HMI and also using the Programming port for the programming that i am trying to due. I am in Pennsylvania and the PLC's are in Long Island NY. So the next time that I go out i will check for the +5V on the pins. What i do not understand is that the other two PLC's at the site are configured the same way and they work fine. Maybe an Electrical surge? I also tried switching to the Com port for the communication between the PLC and the HMI but that did nothing. It seems strange that both ports are bad on 2 of the 4 PLC's.

Thank you for your help.

Kevin, I posted your email here because somebody else might be able to add to my comments. Do you have to use the converter for HMI communications, or can the Red Lion unit support RS485? If the HMI is RS485, you don't need the port's 5 VDC supply. In that case, the HMI would communicate just fine, but the programming software wouldn't be able to talk.

It's also possible that somebody felt the need to change the baud rate or one of the other port parameters. Default port values for the programming software is 19200 baud, Odd parity, 8 data bits, 1 Stop bit.

I have had similar problems with the 90-30 communicating to a Dupline setup. 5 other systems with the same configuration worked fine. After double checking and replacing the Dupline transeaver, the GE com module, cables, configuration setup etc.. in a final act of desperation we replaced the CPU in the 90-30. Apparently the CPU was the problem. Go figure, it alway turns out to be the last thing you check.