The Industrial Raspberry Pi Forum

Hi All!

I was trying to use the ModbusRTU Master on the RS485 (/dev/ttyRS485) port. I would like to talk with Modbus Slave devices, but I found some troubles. The ModbusRTU MASTER was configured as in the tutorial wideo (https://www.youtube.com/watch?v=gaJ6-D4 ... volutionPi), the configuration was saved as start-config, and the driver was reseted. On the picture you can see the configuration: After configuring the hardware I was trying to send some data via the RS485 and the piTest tool. The command I was trying to use was "piTest -r 11,6,h" in order to obtain 6 bythes (3 words) from the slave device. Unfortunately the communication fails - I can't observe any data communication on the rs485 line on the oscilloscope which is connected to the A and B lines of the RS485 port.

Then I decided to just echo this port with command "echo "x" > /dev/ttyRS485" and it was successful - the data communication on the lines was established, so the port is working.

I found same issues with the RS485 to USB converter attached to the USB2 port - communication with piTest gives no transmission with piTest, and works with echoing the port from the terminal line.

How can I configure this port to be accesible with the "piTest" tool. Is there any configuration mode to enable this port to work with the "piTest" tool?

Greetings!


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Hi,

could you please try if the steps mentioned here viewtopic.php?f=10&t=3242 solves your issue? The official patch will be distributed via our repositories this week.

Nicolai

Hi Nicolai
I've tried the solution shown in your prevenious post and it works well. The only thing that must be done is to restart the pimodbus-master.service.
I hope that in the next update of the system this bug will be fixed.

Greetings
Bartek

Hi Bartek,

I'm glad to hear that it is working with the fix.

Nicolai