No signal on RS485 modbus port - RevPi Connect

[b.kolodziej]

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:

RevPi1.jpg (94.14 KiB) Viewed 3015 times

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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[nicolaiB]

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

[b.kolodziej]

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

[nicolaiB]

Hi Bartek,

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

Nicolai