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© Sealevel Systems, Inc. 7106e Manual | SL9268 11/2022
Line Termination Selection via Hardware
Typically, each end of the RS-485 bus must have line-terminating resistors (RS-422 terminates at the receive
end only). A 120-ohm resistor is across each RS-422/485 input in addition to a 510-ohm pull-up/pull-down
combination that biases the receiver inputs. DIP switches SW1 allow the user to customize this interface
to their specific requirements. Each switch position corresponds to a specific portion of the interface. If
multiple 7106e adapters are configured in a RS-485 network, only the boards on each end should have
switches T, PU, and PD ON.
If using the board in an RS-485 two-wire network, enable the two switches labeled ‘L’, which tie the
positive/negative transmit/receive pairs together.
Switch Default
Selection if ON
T
ON
Enables RS-422/RS-485 120 ohm termination between RD+ and
RD–
PU
ON
Enables RS-422/RS-485 RD+ 510 ohm pull-up to 5V (biasing)
PD
ON
Enables RS-422/RS-485 RD– 510 ohm pull-down to GND
(biasing)
L
OFF
Enables RS-485 two-wire mode, connecting TX– to RX–
L
OFF
Enables RS-485 two-wire mode, connecting TX+ to RX+
