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Hello,
Got a uart-to-rs485 converter board from the AliExpress .
Its schematic is very close to this one
It has a 120ohm resistor at data lines however it is not connected (R0 is absent).
As far as I can understand it is something related to impedance matching.
The question is: should I leave it like this (open) or short if all I want is to connect 2 identical modules to make a communication line between two UARTs? The picture below is what I bought, R13 seemed to be R0 from the pic above
I would say you should not short it. Leave it open as it is in the schematics diagram. If it’s a Uart line then it shouldn’t have an issue. But I would say you should check the datasheet and confirm what the manufacturer said about this.
This resistor is for the termination of the line. It is usually mounted at the 485 bus ends to avoid signal reflections and to adapt the bus impedance.
If the bus is short and few devices can work without them and also get a better consumption. If you have data integrity problems, solder the jumper that connects the resistor at one end of the bus.
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