Modbus Master to Master

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Thread Starter

Jap

Gurus,

We have a requirement for talking to modbus PLC (non-redundant) to Honeywell C300 (Redundant). Both are working as modbus master. We need a solution which can support Modbus master to master communication for redundant C300 controller with non redundant PLC.

Your help is highly appreciated.
 
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Michael Batchelor

Two masters cannot talk. That's the nature of Modbus.

But you can get two Modbus to Modbus+ gateways, let the two maters talk to their respective gateway, then let the Modbus+ peer-2-peer devices talk.

You have to define your register map well, and this is not a fast communications pathway. But it can be done.

Or, if you can put another PLC between them with two Modbus slave ports, and allow both masters to have their own slave, this works too.
 
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Lynn August Linse

One could just use any low-cost Modbus slave as a shared resource: one master writes and the other reads. The risk here is that the writing Master 'stops' writing, so the reading master is seeing stale data.
 
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