MVI56-MCM Modbus Controllogix problem

[engrselva]

The MODBUS module is attached w AB PLC. Port 1 (master) has problem in communicating w Mits PLC while Port2 is ok. Port1 can write data to Mits PLC, which is another end of Modbus communication, but unable to read.
Already checked w Mits PLC side using MODSCAN to verify if it is able to read data. it can read. But AB Plc cannot read data from Modsim.
Also did both Warmboot / Coldboot, still unable to read data from Mitsubishi PLC or Modsim.
Any one Please help me to resolve this strange behaviour of the module.

 

[Ken Roach]

Is this a new system you are commissioning, or has it been running for a while and recently failed ?

Is the connection RS-232, RS-422, or RS-485 ?

You must contribute significantly more information, including details about how you have configured and connected the MVI56-MCM module, for anyone to suggest how to make it work correctly.

 

[engrselva]

After lightning strike, the MVI56-MCM was found faulty, both port unable to communicate. So we changed to a new MVI56-MCM, than have this problem. Port 2 ok while Port 1 has problem.

 

[engrselva]

Thanks bradyk
After lightning strike, the MVI56-MCM was found faulty, both port unable to communicate. So we changed to a new MVI56-MCM, than have this problem. Port 2 ok while Port 1 has problem.

 

[Ken Roach]

Thank you for the additional information.

The configuration data for an MVI56-MCM module is stored entirely in the ControlLogix memory and is loaded on a warm boot or cold boot, so this is very unlikely to be a configuration problem.

The next troubleshooting step I would take is to connect to the Diagnostic port on the MVI56-MCM and put it into Data Analyzer mode. You can capture the text it's sending out using HyperTerminal or another terminal program (TeraTerm and RealTerm are my favorites) and post it here for examination.

 

[Ken Moore]

Could the lightning have damaged both ends of the communication network?

 

[Ken Roach]

Port1 can write data to Mitsubishi PLC, which is another end of Modbus communication, but is unable to read data.
I already checked the Mitsubishi PLC side using ModScan32 and verified that ModScan32 is able to read data from the Mitsubishi. But the MVI56-MCM cannot Read data from ModSim software or from the Mitsubishi PLC

.

The problem might be in the physical connection, even in the MVI56 connector that you are using to test the MVI56-MCM to ModSim connection.

If the MVI56-MCM module Transmit wire is OK but the Receive wire is broken, that would make the MCM module appear to be able to Write, but not to Read.

A Modbus Slave replies to a Modbus "write" with a confirmation of success (or failure) but as far as the slave knows, it should perform the Modbus function it's been instructed to perform. There is no second confirmation to the slave that the confirmation reply was received.

I suspect that the MVI56-MCM is recording timeout errors for the "write" commands. The data is probably still arriving at the Mitsubishi controller, but the MVI56-MCM isn't getting a confirmation so it considers the message a failure.

ModSim can probably talk to the Mitsubishi controller because it doesn't use the same cable as the MVI56-MCM module does.

Lightning and other high-energy events are very well known for damaging both ports and wiring. Sometimes the damage is visually evident, sometimes not.

 

[engrselva]

Hi Ken RoachThanks for detailed expalantion . Update you with details.