I am fairly new with using GE plc's . I am using a IC693CMM311 communication module using both ports in RTU mode in a application and would like to know if there is an easy way to monitor when i lose communications with the external device. Are there some sort of status bits for this?

Can you post your external devices that you are communicating with?

I don't recall anything off the top of my head, but I'm shure there is something in the manual. It can be found at http://globalcare.gefanuc.com 

The manual is GFK-0582.

Can you post your external devices that you are communicating with?

I am communicating with some Graphic Panels that a vendor configured for us. The vendors devices reads and writes to a few %R registers in the plc.There are no comm_req in the plc logic at all. All I had to do was set my cmm311 card up to rtu only,plus baud rates. The problem is, when the graphic panes are swithed off, nothing in the registers will change. I need to be able to detect this "off" position. I do notice that the US1 light on the cmm311 constantly flashes while the graphic panel is on, then goes off when GP is off. I was hoping there was a simple way to monitor that led.?

I've been reading the manual and it seems like i may have to set up a comm_req instruction to monitor the serial port. I have never set one up and it seems kinda confusing.

thanks

That is pretty standard that the operator interface requests and posts information to the PLC without any intervention from the PLC program. There probably is a status indicator to let you know that communication is active. It may be hardwired, but it probably does some type of status bit. I would have to look that up; however, the best way to handle checking communication loss either between PLC's or a graphic interface from the PLC side is to work up some sort of heartbeat between the two devices. In a PLC to PLC communication, this would require setting up a timed bit toggle that would be transmitted to the other PLC. The other PLC would check the heartbeat bit to make sure it is cycling as required. This would also work with your situation. The operator interface could be programmed to toggle a bit at a predetermined rate and the PLC could check that. This is an unusual circumstance as most operator interfaces have some way to indicate a communication loss to the operator. Generally if you lose the operator interface, you lose the ability to operate the system and indication is necessary to let the operator know. Your situation is unusual as you want to detect on the PLC side to be able to take action. You mention that nothing in the registers will change. Are you just referring to the fact that the operator cannot enter setpoints or something else?

Russell

i have an extra input pre-programmed in the graphic panel. Im going to wire the keyswitch to that and keep power on the grphic panel when turning the swith off. This will solve my issue for now.

Ok I am glad that helps, but now help me out. How does that take care of your comm status? I am now completely confused....

it wont actually help with the comm status. It will only let me know if the operator decides to "shut off" his panel. I was hoping to use "comm status" as a way to do this. As of right now, if i do lose comms, the plc will not know.