Well after some research I guess I can answer my own question :biggrin: A 120ohms resistor is generally only recommended if the transmission lines are more than 1000 feet, this is also why a rs232 to rs485 converter with a built-in terminal resistor which cannot be disabled is a bad thing.
The...
Is it true that if using a RS485 connection that is short, just a few feet, with any standard RS232 to RS485 converter, then I don't need to use a 100ohms terminal resistor? What is the difference of using a resistor or not using one? what does it do exactly? :confused:
The units I am working with are pretty old, from around 1985, there are two towers of 5 parallel SCR's. Interesting setup and amazingly it still works after more than 20 years of daily use!