Client (master) operations

The Modbus driver supports three types of client devices: ModbusAsyncDevice, ModbusTcpDevice, and ModbusTcpGatewayDevice. Each client device component represents a remote Modbus slave. The host station on a Modbus master network regularly polls these slave devices with requests, which provide Modbus data. Remote client devices listen for these Modbus queries from the master (host station) and send responses. Each type of client supports proxy points. Data exchange occurs with both writable and read-only proxy points, client preset objects, and (if needed) reads and writes to file records, for string data.

Each type of client device is specific to a particular type of parent network. You cannot drag a ModbusAsyncDevice from a palette to a ModbusTcpGateway or a ModbusTcpGatewayDevice to a ModbusTcpNetwork. This is not a problem when working in the device manager for any of the three client networks, as the New window (used to add devices) automatically selects the proper child device component.

The three types of Modbus client devices are similar in that each has a single frozen Points device extension managed by the default Modbus Client Point Manager view. Each Points device extension supports the same type of proxy points, as well as preset and file record objects.

In addition to common Points slots, all three types of Modbus client devices provide similar properties. This includes overrides of network level Modbus Config settings, ping address setup for the parent network’s Monitor ping, device base address configurations for Modbus data items, and slots for configuring device-level polling.