Modbus ExceptionCode 0x01 (IllegalFunction)

Well, either that device has a funny way of telling you you’re reading something you can’t, or it simply doesn’t support the Read Holding Registers request.

I was wrong to point you to those settings - there’s only one kind of request for reading. It’s writing that has a single and multiple version.

Time to start looking at configuration somewhere other than Ignition.

It’s all good.

Yeah, quite strange, especially since all of the registers I am asking for under this device are returning with good, changing values that match the PLC.

I’ll keep digging into the device and it’s communication configuration.

Cheers, Kevin.

With bridges in the middle and a PLC answering to the same query alternatively with good and exception answers, I check for timing issues. Mostly the timeout configured at the bridge for that device or in general.
It’s odd because I’ve never seen an Ethernet bridge answering with an exception code 1 in a case of timeout. The normal response is no response. But I don’t know all of them.

But I’d check if that’s the case first. Are you sure that the tag pointing to Holding register 4413 is updating? Are there other queries raising an exception? Another thing to check is if the update periods match the scan periods configured. if not, you’re missing scans.