RS-485 Resistor Calculator

Using equations from RS-485: Passive failsafe for an idle bus by Thomas Kugelstadt, Senior Applications Engineer at Texas Instruments.

Step 1: Calculate RFS

Supply voltage: V
Tolerance:
Noise margin: mV
RT1:
For proper termination, use 100 ohm for Cat5 cable, 120 ohm for standard RS-485 cable. If your cable is short enough so you don't care about reflections, you can try higher values.

Step 2: Calculate RT2

RFS:

Step 3: Determine max. number of devices

RT2: