MODBUS TCP coms

[rpoet]

Cross-post from my post on the AD Tech Support forum:

Does it seem plausible that a PC communicating with a DL-06 over Ethernet via an ECOM100 could cause the PLC to momentarily hang if the coms fails "ungracefully," and garbage data is sent to the ECOM100?

Here's the situation, and what I think is happening:
I have a PC application reading and occasionally writing a few registers in the DL-06. The PC application is crashing (unrelated to the PLC) and the PLC is hanging for a fraction of a second. I have a hardware watchdog that's tripping the e-stop relay because it isn't seeing the 10Hz heartbeat that the PLC is supposed to be sending. It all happens more or less at the same time, so I have to put in several software traps in the PLC for testing. We'll see what that ends up showing.

I'm going back in tonight for more troubleshooting. I'm planning on pulling the Ethernet cable from the ECOM100 card, as communications with the PC is not critical to testing the process, and seeing if I can get the PC application to crash without taking down the PLC.

Thoughts?


-rpoet

 

[danw]

Almost everything whose primary task is not inherently communications (like a USB/485 converter or an Ethernet switch) has comm tagged on as an after-thought.

Was when I was in a manufacturing environment 35 years ago, still is today. Mr. Morley did not invent his PLC to communicate to other PLCs, he invented it to replace relay logic.

So is your scenario plausible? Absolutely, in my book, even more likely as the trend to out-source the development of comm because comm is not within the core competence of the product itself.

Please keep us posted on the outcome.

Dan

 

[rpoet]

For anyone interested, here's the outcome of my MODBUS coms issues:

http://forum.automationdirect.com/showthread.php?p=54997


-rpoet

 

[danw]

thanks