Pi zero w, modbus rtu, arduino

Hello everyone.
I'm trying to connect a pi zero w with an arduino UNO using modbus rtu protocol. I use the usb integrated on pi pcb to connect to arduino's usb.
Arduino has a modbus program that I tested before with modscan and works properly, but I can't connect node red with it. I'm working with modbus read node from modbus contrib.
I can't find out what is happening. I tested all kind of baud rate, format message and different servers(ttyacm0, ttyso, ttyserial1, ttyserial2 but It doesn't work.
I notice that node-red can't send any message to arduino because comunication lights on arduino pcb are always off.
Could anyone please help me with this?
Thanks

Hi

Have a look at this article about configuration of the serial port on a Pi

Thanks a lot. You are very kind.
Finally I did it. I did install raspbian and node-red again and everything started to work.
I'm going to struggle with how to represent data on debug window. As you notice, I'm a beginner on node-red and on many other things related about code.
Have a good day.

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