About Modbus Async networks

Each ModbusAsyncNetwork requires a serial port (typically, RS-485) on the host JACE platform. The JACE connects on the Modbus RTU or ASCII network and functions as the Modbus master.

Figure 6. ModbusAsyncNetwork with JACE as master device, here on an RS-485 Modbus RTU network

Communications rates are typically at 9600 baud, and the network transmission mode (protocol) may be either Modbus RTU 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 (as noted), networks are typically smaller. Depending on the number of available COM ports, a JACE may support multiple Modbus Async networks.

Figure 7. ModbusAsyncNetwork in JACE station

The station acts as 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.

Modbus Async Network configuration is straightforward, using the property sheet of the network object.