Impulse 3440 User Manual
Page 12
Card
Setup
Sealevel Systems ULTRA COMM+422 Page
9
Line Termination
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-530/422/485 input in addition to a 1K ohm pull-up/pull-down combination
that bias the receiver inputs. Headers J1E through J4E allow the user to
customize this interface to their specific requirements. Each jumper position
corresponds to a specific portion of the interface. If multiple
ULTRA COMM+422 adapters are configured in an RS-485 network, only the
boards on each end should have jumpers T, P & P ON. Refer to the following
table for each position’s operation:
Name Function
P
Adds or removes the 1K ohm pull-down resistor in the
RS-422/RS-485 receiver circuit (Receive data only).
P
Adds or removes the 1K ohm pull-up resistor in the RS-422/RS-
485 receiver circuit (Receive data only).
T
Adds or removes the 120 ohm termination.
L
Connects the TX- to RX- for RS-485 two wire operation.
L
Connects the TX+ to RX+ for RS-485 two wire operation.
P
P
T
L
L
Figure 11 - Headers J1E - J4E, Line Termination