Slave Id.  Add a slave by entering a slave identifier in the text field, and then press Add. (The new slave appears as a tab labelled with the slave id in the main window.) The Slave Id is what is called the "slave address" in the original Modbus specification, and is called the "unit identifier" in the Modbus/TCP specification. It should be in the range 1 to 255. A zero slave identifier is used in write requests as a broadcast identifier (each slave that receives the message should store the values supplied in the request, but should not send a reply). The original Modbus specification limited the range of slave identifiers to 1 to 247, for no apparent reason. The Modbus/TCP implementation guide suggests that Modbus/TCP slaves that can be uniquely identified by their IP address should use slave identifier 255. You may not add a slave when ModMultiSim is serving the master or running the slave simulation (i.e. when Serve Masters or Run Slave Simulation are highlighted).

Slave Name. This is an optional field. It enables you to have more meaningful identifiers for each slave in the main window than just the slave id. For the currently selected slave (i.e. the slave's whose registers are visible), the name will be displayed above the slave registers panel of the main window. The name may be entered at the time the slave id is added, or it may be added later. To add it later, or to edit a slave name that has already been added, enter the slave's id in the Slave Id field to enable text to be entered in the Slave Name field.