Modbus RTU communication Toshiba PLC - Hitech HMI

3 posts in this topic

Hi Everyone,

I am trying to connect a Toshiba TRSPUX10A plc to a hitech PWS6600 HMI (Beijer electronics). I am using RS485 connection, and trying to get the communication going between the plc and hmi using Modbus RTU protocol.

The PLC is slave and and HMI is Master, and I have a Modbus slave tag table for the plc.

HMI Software: ADP3

PLC Software: TRPGMS01

Our supplier of the product cannot assist me as he passed away, and the manufacturers of the systems refer me to each other but with no luck. I have asked numerous system integrators however they only work with the systems they supply.

I want to read a Modbus slave tag: Holding register 4500001 in the plc and have it displayed on the hmi.

Please advise if anyone could assist.

Kind Regards







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Well, supplier is only one link in support chain. Did you contact manufacturer of your HMI? 

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See my lengthy introduction to Modbus in this thread (4th post down):

How do you know the PLC Modbus slave register is 450001?  Where did that register number come from?

The PLC has to be configured as a Modbus slave with a slave node ID number (maybe it defaults 1, sometimes 247, who knows?  You need to look it up and determine what the slave ID number is.

You need to research how to set up your HMI as a Modbus master.  It's somewhere in the HMI documentation, it has to be because an HMI has no I/O, it has to read its data digitally from some device.

You need to setup the serial settings on both devices to be the same (baud rate, 8 bit word, parity).

You need to dig out the wiring connections for the RS-485 connections.  A to A, B to B or + to +, - to -, unless one of them does it backwards, which happens more than it should.    If it's 4 wire RS-485, the jumper + to +, - to -.   You should connect signal ground with a 3rd wire.

If you can test  on the bench it's a lot easier than running back and forth.

I'd use a generic Modbus master to read the PLC's value first to confirm that you can actually read data from 450001 and interpret it (integer, floating point, long integer, whatever format).

Then start working through how the HMI reads a Modbus value.



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