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Have trouble getting modbus comms from a Omni Flow Computer 6000 through a Modicon multiplexer BM85 to a Modicon Quantum PLC with Modbus Plus on the PLC. Already have modbus data coming from a Allen Bradley PLC and HMI to the Modicon with no troubles. These are slave devices though and i need to be a master. I can talk to the Modicon PLC through the Multiplexer to do any programming to the PLC. Any ideas?

Hello,

Read the Omni flow MODBUS documents. I am not being flippant.

Omni flow computers can support standard MODBUS but really are ENRON MODBUS.

You must be sure to read the correct registers and have the flow computer set up correctly.

Good luck,

Mark
http://www.peakhmi.com/

Mark is correct - the Omni flow has a mode which I believe they call 'Modicon Compatibility Mode' which defaults off, but allows most (all?) Modicon devices to talk to the Omni Flow, so the BM85 should work.

Also, you may need to avoid the magic-sized, user-configured region of the Omni register map where you poll say 100 registers but might only get 6 bytes back (or even 0 bytes). Few Modbus masters support such unpredictable response sizes.

Hi,

FieldServer using their gateway can convert Modbus Omniflow to Modbus RTU, have a look at www.fieldserver.com

Thanks,

Richard