Modplus RTU Comm Problems


Thread Starter


I am having issues with slave devices dropping offline about once every 10-15 minutes or so. Has anyone had this similar issue and what have they done to resolve? I can see the master tx 3 times, and with no response from slave after 3rd time, it times out and goes offline, then moves on to another slave device. This happens to only 1 or 2 slave devices in a series modbus rtu circuit with about 9 slaves in series, at different time intervals. I have checked the wiring, grounding, termination resistors, comm, programming of slaves, o'scoped the signal, all these look good. Any other help would be appreciated.
Have you set it up in a full duplex or half duplex mode? Can you sequence your messages to occur only when the previous message has completed (either completed succesfully or failed).
I have seen this before.

Our products do this, and it is configurable within the newer systems. Basically we perform a self-test every 15 minutes which lasts about 10-15 seconds. During the self-test NOTHING else happens. No communication, no calculation of the process variable, nothing... it is normal operation.