Hi There,
Could someone explain how the MVI56-MCM determines if a slave device is failed or not. I have written a simple timer based ladder that triggers the module to update it's ".P1Slaves(x)" registers (4 seperate triggers per MCM module). The problem I have is that on every other scan of my timer logic some of the slave registers report healthy the next scan bad! I have used a Modbus monitor on my network and the data stream does not show any errors to the affected devices. I've 'scoped the RS485 network too and the waveform looks nice and square and no noise.
I have tried slowing down the poll interval of my commands, increased timeouts, retry counts, interval between commands, all to no real effect. I just get the same problem, just slower.
I understand that the MCM puts the slave device 'to sleep' for the duration of the 'ErrorDelayCntr' and then wakes it up again to retry if it can now talk to the device.
Does the MCM determine if a device is bad by using the retries and timeouts and then if it cannot communicate it then updates the "slave status register" or does the MCM look for a specific watchdog or heartbeat from the slave device?
I have 5 MCM modules on my control scheme all talking to a varity of Schneider and Alstrom breakers and each module has the same problem.
Many thanks for whatever advice anyone can offer.
