Communication Issues with SLC5/03 and AB port splitter

Just was wondering if there was a way to write something in the program to recognize when the RS-232 communication is not working between PLC to Port Splitter, then to modem and HMI. It seems to work fine when we poll a little Data from PLC but if we start to pull alot more information via Modem for Scada, it tends to freeze the Port splitter. PLC is running still but would like to detect when RS-232 fails to POrt splitter.

You could set up a Scada heartbeat bit in processor memory. The Scada system would be responsibility for setting and clearing this bit periodically and the SLC would have timers monitoring the state of the bit. If communications break down, the bit won't change state and a monitoring timer would finish and set the fault.

Could you give me an example as to what it would look like in the SLC program?

I am not familiar with the port splitter, but you might be able to monitor the comms active status (S:33/4) bit in the PLC to detect when it stays off for a significant period of time.

I am not certain that it will go off, but I suppose you could test it.

As for the heartbeat logic, there are a couple of ways to do it. One example:

The HMI monitors B3/0 and sets B3/1 to match it. If B3/0 does not change states within 5 seconds, a comms alarm is set.

The PLC monitors B3/1 and sets B3/0 to the opposite state. If B3/1 does not change states within 5 seconds, a comms alarm bit is set.

Both bits should "flicker" at a pretty quick rate when everything is working normally.

Another method:

The HMI monitors N7:0 and sets N7:1 to match.

In the PLC, if N7:1<32767. Add 1 to N7:1 and write the result to N7:0. If N7:1>=32767, CLR N7:0.

I like the second method, since it makes it easier to "see" the rate of communication, and identify aberrations.

Paul

Thanks so much Paul for taking time to read and answer my question. I will try both methods and see what I get for my results.

You're Welcome!