About Modbus Plus network

I have a Modbus Plus network which connects four Modicon Quentium PLCs.Now it is required to have another two new Modicon Quentium PLCs connected to the network.Then,what should i do to achieve it?What hardware do i need?How is it configured?What do i have to be aware of?Thank for any advice.

To some extent the answer to your question depends on the specific CPU number you are using. The Quantum has built in Modbus Plus on most of the CPUs, so that shouldn't be a problem. However, Modicon uses these goofy terminator kits for the wiring, and you should talk to your local distributor about this.

As far as programming, it depends on whether you are using peer COP or programmed message blocks for the data exchange.

Most of your questions are dependant on the physical arrangement of your existing network and where you plan to add the new devices. A copper wire (2 conductor) Modbus Plus network needs to have a single trunk line with all of the drops being "daisy chained". There are three different types of tap devices available from Schneider Electric (these are the terminators Tom mentioned). A standard Modbus Plus network can have 32 devices. If you add a booster/repeater you can expand the network to 64 devices.

Adding additional devices may not impact your existing application programs. As Tom stated, there are two different methods for exchanging data across a Modbus Plus network, both methods may exist in any one system. If your existing equipment does not need to initiate communications to the new processors, you will not have to make any changes at all if you use the MSTR function block. If you are using Peer Cop, then your existing processors will have to be re-configured.