Modbus device ID

The company I work for is developing a controller that has three
communications ports:  two RS485 and one TCP.  Modbus TCP and Modbus
RTU Master/Slave will be implemented.  It has been proposed that each
port have a different Modbus device ID, rather than one global ID.

I contend there is no benefit to this, and only adds confusion for
integrators.  Does anyone know of a precedent for this?

Thanks in advance.

> I contend there is no benefit to this, and only adds confusion for
> integrators.  Does anyone know of a precedent for this?

I would go for a slave ID for each port.

If I am a master it might be that I am talking with several slaves and 
each slave must have a unique ID. If your address is 5 and I as the 
master already have a slave with ID 5 then something has to change.

If you are allowing both 485 ports to be RTU slaves then how can you not 
make each port have a different ID? Or are you not going to allow them 
on the same chain. That would not be....

As a master I communicate to one slave device with two ports(hot stand-
by). I want both ports to have a different ID. 

I have worked with MANY slave devices over the years and I can not 
recall one that had a global slave device ID for multiple ports. Just 
look at how MODICON does a multi-port PLC. 

I can think of several other reasons but I will leave it at it will not 
be a confusion for integrators.