Failed to Read Modbus RTU Master
Failed to Read Modbus RTU Master
I have trouble modbus rtu master setting on the Revolution Pi Connect S. After setting modbus master in pictory it won't show the output or input. Using RevPi for modbus master, and VSD ATV-320 for modbus slave. Trying to connect directly to a pc using VSD ATV-320 it can already. Why is using RevPi problematic in modbus connection? I have connected it to another modbus slave such as TK4S, it also works.
Re: Failed to Read Modbus RTU Master
Hello Anam,
Please use the steps in this helpful checklist to check whether the physical connection is correctly assembled:
RS-485 Checklist
If this works, then you are not far away from Modbus communication. Then take the steps from this checklist and check whether the setup is correct:
Modbus Checklist
I can also recommend this video tutorial - Modbus RTU Master:
https://revolutionpi.com/en/tutorials/video-tutorials
Please use the steps in this helpful checklist to check whether the physical connection is correctly assembled:
RS-485 Checklist
If this works, then you are not far away from Modbus communication. Then take the steps from this checklist and check whether the setup is correct:
Modbus Checklist
I can also recommend this video tutorial - Modbus RTU Master:
https://revolutionpi.com/en/tutorials/video-tutorials
-
krshackleton
- Posts: 1
- Joined: 25 Feb 2025, 03:51
Re: Failed to Read Modbus RTU Master
I also have a problem with Pictory and Modbus RTU Master. I found the tutorial "https://revolutionpi.com/documentation/ ... tu-master/" to lack a couple of important aspects (which is to a degree true in all the RevPi tutorials):
- there was no overview of what was to be achieved. In this case using Pictory to set up a Modbus RTU Master. Where does this configuration sit? Is it a global service? How can the results of this configuration be used?
- there was no useful debugging instructions. It took some time before I found that "check the Modbus_Master_Status register for the error code" meant "open a console and use piTest -r to . ."
There is a utility mbpoll which can be installed with apt. The command (using the necessary values):
mbpoll -m rtu -a 1 -r 0x03e8 -0 -c 3 -t 3 -b 9600 -P none -v /dev/ttyRS485
does produce the expected results, short-circuiting the first two suggestions offered. The 3rd link to video tutorials points to the web tutorial..
I also ran
$ tail -50 /var/log/revpi-server.log
and found an alarming number of Python exceptions, including some nodered messages though I have disabled nodered in Cockpit.
It seems a lot more simple to focus on command-line Python.
- there was no overview of what was to be achieved. In this case using Pictory to set up a Modbus RTU Master. Where does this configuration sit? Is it a global service? How can the results of this configuration be used?
- there was no useful debugging instructions. It took some time before I found that "check the Modbus_Master_Status register for the error code" meant "open a console and use piTest -r to . ."
There is a utility mbpoll which can be installed with apt. The command (using the necessary values):
mbpoll -m rtu -a 1 -r 0x03e8 -0 -c 3 -t 3 -b 9600 -P none -v /dev/ttyRS485
does produce the expected results, short-circuiting the first two suggestions offered. The 3rd link to video tutorials points to the web tutorial..
I also ran
$ tail -50 /var/log/revpi-server.log
and found an alarming number of Python exceptions, including some nodered messages though I have disabled nodered in Cockpit.
It seems a lot more simple to focus on command-line Python.