Modbus RS485 problem


#1

Hi All,
I have an node red project where i need to connect to modbus registers.
Now i have had it working on an embeddedpi connected to ttyAMA0.
But suddenly ,and i don’t know why, its not working anymore.

I am reading sample modbus registers of a Simply Modbus slave on a Windows Vista laptop.
I have a usb to RS485 converter connected to the laptop and the same converter to a rpi 3 (ttyUSB0) and then i don’t have any problems. It just works. And this worked before on the embedded pi aswell, with ttyAMA0.

At this moment when i do a read on the ttyAMA0 it does receives the request on the windows slave. That is all working. I see the slave is also sending a respons of the read registers. But this respons is not received on the embeddedpi anymore. It gives a timeout on the node red module.

Is there something i mis? It looks like sending is working correctly. But receiving isn’t anymore.


#5

Hi @RDB
Is the device running resinOS?


#6

Yes it is running: Resin OS 2.9.6+rev1 (prod).
I have added a issue on the git of the node module too.

But i am not sure if its a hardware issue, setup issue, node issue…


#7

I seems the problem of the usb to rs485 converter i used.
I changed them for another type and now its all working again.