Modbus and HMI

[robjcook]

Hi group first time I have visited this site looks great.

Has anybody had experience setting up comms between a modicon PLC and a Mitsubushi E100 HMI using modbus. I can't get them to talk to each other over the network although I have set the terminal up for Modbus but not sure if it needs to be setup as a Slave RTU or master ?

Any comments please

 

[Jim Dungar]

Politically Correct (?)

Your HMI is the requester (master) and the Modicon PLC is the responder (slave). Make sure the HMI and PLC are both set up as RTU (default = 9600 baud, 8 bit, Even parity, 1 stop bit) or as ASCII (default = 2400 baud, 7 bit, Even parity, 1 stop bit).

 

[Steve Bailey]

Modbus RTU doesn't have a peer-to-peer mode, so one of the devices needs to be the master, the other the slave. Generally, the HMI device is the master.

The obvious things to check are that the baud rate, parity, handshaking, data bits, and stop bits are the same for both devices. Make sure that the master is asking for data from the same ID number that the slave is set as. Try to get a cabling diagram showing the connections between the HMI and PLC you're using. Make sure they're both set for the same electrical standard (RS232 or RS485).