The Industrial Raspberry Pi Forum

Posted: **19 Nov 2020, 13:35**

Hello,

I want to set up a gateway betwen two networks which enables modbus communication. Another requirement is to do so through the web interface of revpi connect. On both sides (on both networks) I only have one slave and the gateway should periodically update one side with the registers of the other side. I think that by having two masters on the revpi who share their registers it could work out but I can't see how to do so.

Is it possible at all ? Is there a recommended way ? Being able to simply forward the modbus messages could work out as well, I can have one network hold a master.

Marc

Posted: **24 Nov 2020, 10:20**

Hi Marc, this is an interesting requirement.
I have understood your requirement looks like this:

Code: Select all

[Modbus TCP Slave] - [Modbus TCP Master] - [Modbus TCP Master] - [Modbus TCP Slave]

Just configure two Modbus TCP Masters so they will communicate with each slave.
Now comes the "glue" you just have to write some code that copies the Output data from Master A to Input data of Master B and vice versa.

With RevPiModIO Python library it would consist of just a few lines of code. Just an example to point you there:

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#!/usr/bin/env python3
# BitMirror.py
# Mirror DIO channel 1 input to DIO channel 1 output

import revpimodio2
import time

rpi = revpimodio2.RevPiModIO(autorefresh=True)

while True:
	rpi.io.O_1.value = rpi.io.I_1.value
	time.sleep(0.02)

But you could also use the raw method by just looking at the offsets via "piTest -d" and seek and write them, more or less like so:

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#!/usr/bin/python3
import time
#LED ein- und ausschalten
f=open("/dev/piControl0","wb+",0)
while True:
	f.seek(119)
	f.write(b'1')
	time.sleep(1)
	f.seek(119)
	f.write(b'0')
	time.sleep(1)

The Industrial Raspberry Pi Forum

Sharing registers between modbus masters

Sharing registers between modbus masters

Re: Sharing registers between modbus masters