Termination resistors¶

When a RS485 bus line becomes long, it is necessary to terminate it with 120 Ohm resistors. This ensures signal integrity.

What long constitutes is use case dependent. For the Plant Controller termination resistors shouldn't be theoretically be necessary unless the line is longer than 2km. But, if your line is very long, and you are experiencing problems with the signal to and from parts connected to the RS485 bus, connecting termination resistors might help.

The resistors won't be under very heavy load so basic ½ watt 5% leaded resistors will do the trick.