Mitsubishi PLC and inverter communication case

Modbus is a serial communication protocol invented by Modicon for communication between its PLC and host. Its physical layer adopts asynchronous serial standards such as RS232 and 485. Due to its openness, it is adopted by a large number of PLC and RTU manufacturers. The Modbus communication method adopts a master-slave query-response mechanism. Only when the master station issues a query can the slave station respond, and the slave station cannot actively send data. The master station can issue a query to a certain slave station, or broadcast information to all slave stations. The slave station only responds to queries sent to it individually, not broadcast messages. The MODBUS communication protocol has two transmission modes: RTU mode and ASCII mode. Mitsubishi 700 series inverters can use the ModbusRTU communication protocol from the RS-485 terminal for communication operation and parameter setting.

Target:

1. Mitsubishi PLC: FX2N+FX2N-485-BD
2. Mitsubishi inverter: F700 series, A700 series.

The two are connected via a network cable, see the figure below for details.

Connection diagram of FX2N-485-BD and n inverters

1. Mitsubishi inverter settings

When the PLC communicates with the inverter, the communication specifications must be set in the inverter. After each parameter initialization, the inverter must be reset or the inverter power must be turned on and off.

When communicating with the ModbusRTU protocol, Pr551 must be set to 2, Pr340 to a value other than 0, and Pr79 to 0, 2, or 6. When communicating with the ModbusRTU protocol through the RS-485 terminal, it must be run in NET network mode.

2. Mitsubishi PLC settings

Set the communication format D8120

The setting value of D8120 is 0C87, that is, the data length is 8 bits, the parity check is 1 stop bit, the baud rate is 9600pbs, ​​and there is no header character and terminator character.

After modifying the D8120 setting, make sure to turn the PLC power on and off once.

3. Communication procedures

Some PLC programs that use the ModbusRTU protocol to communicate with the inverter are as follows:

4.Procedure Description:

1. When X1 is connected once, the inverter enters the forward state.
2. When X2 is connected once, the inverter operating frequency 60HZ is written.
3. When X3 is connected once, the inverter enters the stop state.

When the inverter instruction address is 0 in the instruction, it is a broadcast instruction. All slave inverters only accept instructions from the PLC and do not send response information to the host.