Modbus is a client-server protocol when it is used over serial communication networks. This protection relay implements the server side of the protocol. Depending on the chosen physical serial interface it is possible to build multidrop networks or point-to-point communication connections.
There can only be one Modbus client unit on a Modbus serial network. The Modbus client unit communicates with one Modbus server unit at a time. Usually the client reads, or scans, data from the servers cyclically. The client can also write data or give commands to the server units. Each server unit has a unique unit address. Thus, the client can identify the server with which it communicates. The Modbus standard also supports client broadcast transmissions.
Modbus serial protocol uses two link modes: Modbus RTU and Modbus ASCII. Both modes are supported by this protection relay.