Slave Polling Only Once and then not Responding

ABB Drive HMI Panel model ACS550 communicating through RS485 causing an error, others the same HMI panel communicating but the same panel causing the issue.

While reading the registers from Modscan software it is polling once but after one poll the controller stops communication. I tested it with the different units but its working fine for all why it is not communicating with that unit. Maybe it is gone to the Listening Mode?
 
I think the situation is that the HMI panel, a MODBUS master, is polling the drive, a MODBUS slave, and is causing a error/fault.

It is not clear whether Modscan can read data from the drive successfully or not. What is the result of Modscan reading the drive?

"I tested it but its working fine" contains no useful information because no one knows what the multiple 'it' devices are. Please restate the situation without the word 'it'.

What device seems to poll only once? What is the evidence/indication that a master's polling happens only one time?
 
M

Manoj Kumar Gupta

Don't actually know the exact issue, but I tested with exact same 2 or 3 Drive HMI. Others are polling each second (Normal Response), but only one panel is there which polls only once whenever the Drive is Restarted. I think the Modbus has gone to Listen Mode, what happens if the Modbus goes to the Listen Mode will it respond only once when the device is restarted.

We have also tested with our Communication device which is programmed for reading the register Addresses 40110, 40109 and other required addresses. Its also reading in the 1st iteration and not responding anything in the rest iterations.

Before this polling error, the panel was responding fine and working ok while communicating through RS485. We were experimenting with the write operation with the Drive and this happened.

Please tell me the steps to debug the same.
 
W
If the Master is able to talk to other slaves but only polls the one slave and quits, it is likely that you are getting an error message from the slave or an I/O timeout and your master does not handle the error and quits or sits there awaiting a response from the slave (e.g. I/O timeout).

You need to look at the Modbus messages from the Master and the response from the slave. This is probably the only way to see what is going on.

William (Bill) L. Mostia, Jr. PE
ISA Fellow, FS Engineer (TUV Rheinland)

Winner of the 2018 ISA Raymond D. Molloy Award

WLM Engineering

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Any information is provided on a Caveat Emptor basis.
 
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