Modbus Question

This is probably a dumb question, but I am very new to modbus communications.

When a slave on my modbus rtu to tcp gateway shuts down I obviously get some read errors when polling in Ignition, however when I lose one slave, I lose all communications. If I delete the tags that are reading from the device that is shut down, the rest of my tags from the devices that are powered up start reading again with no issues. Is there a common practice for how to handle this?


When a slave device goes down do your logs get read timeout errors or do they get errors about receiving an ExceptionCode such as GatewayTargetDeviceFailToRespond or SlaveDeviceFailure?

Thanks for the response. I was getting timeout errors.

When I adjusted my timeout on the modbus gateway from 10 seconds down to 1 it appears my problems with the good slave went away. My scan class in Ignition was set for 10 seconds. Could there be a correlation here? Thanks!

Turning the timeout configuration of the Modbus gateway down to less than or equal to the “Communication Timeout” you have configured for the device in Ignition is probably ideal (2000ms by default).

When it’s longer like you had it, you end up getting a bunch of timeouts in a row, and then you end up reconnecting, all the while the other slaves being addressed on the connection aren’t getting any requests sent out.