ModBus RS 485 network


Thread Starter


Hello ,
In a ModBus RS485 network , generaly terminating resistors are used along with a capacitor. I would like to know how do we calculate the value of the resistor and capacitor for both ends and do we need resistor and capacitor both, or only resistor is enough.
I appreciate if any body can hint about this

Schneider Electric's Momentum Processor Guide #870USE10100 has information on 2-wire and 4-wire RS485 cabling. For 2-wire they recommend (1) resistor set and (1) set of jumpers. For 4-wire they use (2) resistor sets.

They list resistors as 1/4W, 121 ohm, 1%.

another reference for serial communications is """ .