Modbus is a Modicon PLC and the host for its communication between the serial communications protocol invented. The physical layer RS232, 485 and other asynchronous serial standard. Because of its openness and by the amount of PLC and RTU manufacturers to adopt. Modbus communication with the Lord from the way the query - the appropriate mechanism to send queries only the main points from the station to give response can not take the initiative to send data from the station. Master station can send one check from the station can also broadcast messages to all from the station. Separate from the station only to respond to queries sent to it, not respond to radio messages. MODBUS communication protocol has two modes of transmission: RTU mode and ASCII mode. Mitsubishi 700 Series converter from RS-485 terminal can use ModbusRTU communication protocol for communication operation and parameter setting.
Object:
1. Mitsubishi PLC: FX2N FX2N-485-BD
2. Mitsubishi Inverter: F700 Series, A700 Series.
Through the network cable connection between the specific reference to the figure below.
FX2N-485-BD and n inverters connected graph
1. Mitsubishi Inverter settings
Communication between the PLC and frequency converter, the communication specifications must be set in the inverter, each parameter initialization settings, need to reset the converter or inverter power off.
No. Name Description parameter settings
Pr331 Communications Station No. 1, No. 1 set the converter station
Pr332 communication speed of 96 set the communication speed is 9600bps
Pr334 Parity Stop bit length 2 even parity, 1 stop bit length
Pr539 communication check time not to communicate checksum 9999
Pr549 Select 1 ModbusRTU agreement protocol
Pr551 PU mode operation right choice 2 PU PU operation mode of operation as the interface to the right
Agreement for ModbusRTU communicate, Pr551 must be set to 2, Pr340 is set to a value other than 0, Pr79 is set to 0 or 2 or 6. Through the RS-485 communications terminals to ModbusRTU agreement, you must run the NET network mode.
2. Mitsubishi PLC s setting
Set on the communication format D8120
D8120 set value 0C87, the data length is 8 bits, even parity, 1 stop bit, baud rate 9600pbs, without the title character and the terminator.
Modify D8120 settings, to ensure that PLC power off once.
3. Communication program
Communication protocols and transducer used ModbusRTU part of PLC programs as follows:
4. Procedure Description:
1. When X1 connected once, inverter is transferred into the state.
2. When connected to an X2 after the write inverter operating frequency of 60HZ.
3. When connected to an X3, the inverter into the stopped state.
When the directive, the inverter instruction address is 0, the broadcast instructions, all from the station PLC converter only accepts an order, do not send a response message to the host. -->