ABB NETA-21 - Bus Termination Configuration

Electrical installation 31
Switching on the bus termination
To avoid signal reflection, add 120-ohm termination to the last devices at each end of the
bus line.
You can use the internal resistor of RS-485/EIA-485 adapters or an external passive
termination resistor. The internal termination switch activates also the pull-up and pull-
down resistors.
EIA-485 device EIA-485 device EIA-485 device
Ter mi nati on
activated
Ter mi nati on
activated
Te r m i n a t i o n
deactivated
Termination
deactivated
EIA-485 device
Te r m . Te r m . Te r m . Te r m .
ON OFF
OFF ON
J2
J2
J2 J2