Modbus. Slave to Slave comms.

Gents,

Is it possible to send data from one slave station to another on Modbus?

I have a network with a PC running as a Modbus Master out of it's serial port, (sorry driver unknown at this point in time), and then a Modicon Momentum processor and several AB MicroLogix 1500's as slaves.

What I want to do is get data from the Modicon processor to the MicroLogix 1500's using some kind of messaging function.

If this where all DF1 Half duplex I know I could do it, but does Modbus typically support this kind of thing?

You will need to make the master read the required data from the Modicon slave and then write that data back to the AB slaves.

A serial Modbus network can only have one active Master at a time.
Only if your PC was not active could your Momentum do what you want.

How about adding a second Modbus port to your Momentum? The PC could be the master to the Momentum which would then be the master to the MicroLogix.

Good thinking Jim. I'm just not as familiar with Modicon as I should be. The project is just a proposal at this stage and I've just realised that I'm short on some detailed info about the existing installation...but if what you suggest is doable, then it looks like the way to go.

Thanks