schexb
Member
Going to preface this by saying I am a complete modbus newbie, so apologies if my terminology is off...
We have a Prosoft PLX31-EIP-MBTCP modbus module set up to communicate with our CompactLogix PLC (5069-L310ER). There is an external service associated with one of our manufacturing processes that writes a heartbeat to one of the coils on the PLX module, and then reads the same coil. Problem was the heartbeat wasn't.... beating. On a call w/ our IT and the external company's service tech, we confirmed the connection is good, they can see our PLC, etc - but the heartbeat kept failing, and we weren't seeing the bit flip in the PLC. The issue was resolved when we picked a higher numbered coil and it started flipping on and off as expected.
First thing I did was cross reference the PLX tag to see if it was used anywhere else in the PLC, which it wasn't. Soooo questions:
Thanks in advance!
We have a Prosoft PLX31-EIP-MBTCP modbus module set up to communicate with our CompactLogix PLC (5069-L310ER). There is an external service associated with one of our manufacturing processes that writes a heartbeat to one of the coils on the PLX module, and then reads the same coil. Problem was the heartbeat wasn't.... beating. On a call w/ our IT and the external company's service tech, we confirmed the connection is good, they can see our PLC, etc - but the heartbeat kept failing, and we weren't seeing the bit flip in the PLC. The issue was resolved when we picked a higher numbered coil and it started flipping on and off as expected.
First thing I did was cross reference the PLX tag to see if it was used anywhere else in the PLC, which it wasn't. Soooo questions:
- I am familiar with messages - is it possible there could be a message somewhere else overwriting this? Could I even - in theory - use a message to overwrite this specific tag?
- Regardless of the answer above - is it possible to see message's being written to a PLC without knowing where they are coming from or what they might be writing to?
- If it's not a message, where else might make sense to look?
Thanks in advance!