Hi All,

I am using 4 wire RS-485 for Modbus communication. I have 5 Modbus RS-485 slaves which should communicate with DCS. The DCS (Master) is having one RS-485 Modbus port.

My question is can I connect the 4 wires from each RS-485 Modbus slave device in parallel and then send it to Modbus Master RS-485 (DCS)?

Will this configuration work? What will be the things which I need to take care of?

Regards,
has100

 

> can I connect the 4 wires from each RS-485 Modbus slave device in parallel
> and then send it to Modbus Master RS-485 (DCS)?

Parallel? Yes, but it depends on whether the RS-485 connection on the DCS side is 4 wire or 2 wire.

If it is 2 wire on the DCS end, then you convert the 4 wire to 2 wire by jumpering (+) to (+) and (-) to (-), or A to A, B to B and use 2 wires.

Connecting a 3rd wire to signal ground from device to device is also advisable.

> What will be the things which I need to take care of?

Read my reply in this thread:
http://control.com/thread/1411750426#1411826356

Substitute your slave device wherever it mentions the word 'drive' (the slave device in the thread).

Get one working first, then add one at a time.

 

Probably not, a daisy chain is recommended. The impedance gets very low with parallel connections.

Regards
cww

 

I must clarify. They are normally bussed in parallel. But it sounded
like you want to run a wire to each and connect the near ends in
parallel. Like a star topology. That can cause problems, especially if all the legs are terminated as they should be. The proper way is to go from node to node terminating at the ends. So, they are in parallel along the transmission line, rather than 5 transmission lines in parallel.

Regards
cww