If the host has multiple RS-485 or RS-232 ports to be used for client (master) access to Modbus networks, add one ModbusAsyncNetwork for each physical port.
Communications rates are typically at 9600 baud, and the network transmission mode (protocol) may be either Modbus RTU (Remote Terminal Unit) or Modbus ASCII (either one is supported). If Modbus RTU over RS-485, up to 31 slave devices may be attached—or more, if repeaters are used. The address range for Modbus devices on a serial network is from 1 to 247, however, networks are typically smaller. Depending on the number of available COM ports, a host may support multiple Modbus Async networks.
The station acts as the Modbus master to all other Modbus devices on the attached COM port. Each child device is represented by a ModbusAsyncDevice, and has a unique Modbus address (1 to 247), as well as other Modbus config data and starting addresses for Modbus data items (coils, inputs, input registers, holding registers). There are typically many child ModbusAsyncDevices.
Only one ModbusTcpNetwork is needed, even if the host has two Ethernet ports connected to two different (non-routed) TCP/IP LANs. The destination IP addresses of child ModbusTcpDevices automatically determine the Ethernet port.
The driver supports one or more ModbusTcpGateways. Often, Modbus TCP/serial gateways are on the same LAN as other Modbus TCP devices.