Each RS485 port has an adjacent three-position biasing switch.
Each switch has these settings:
- BIA - (Default, middle) RS485 biasing and termination: 2.7K Ohm bias resistors with no termination resistor
- END - RS485 biasing and a termination: 562 Ohm bias resistors and 150 Ohm termination resistor
- MID - RS485 biasing or termination: 47.5K bias resistors with no termination resistor
Often, adding RS485 biasing can improve communications by eliminating indeterminate idle states. For example:
- BIA - (Default, middle) is often best if the RS485 trunk needs biasing when the controller is not installed at the end of the
trunk.
- END - is often best if the controller is installed at the end of an RS485 trunk of devices that is not already biased.
- MID - is often best if the controller is put in the middle of an already-biased RS485 trunk.
If desired, you can change the position of an RS485 port’s bias switch while the controller is running. Each RS485 port has
two LEDs. Refer to “RS485 LEDs” for details.