Impulse 7205 User Manual
Page 7
Installation
Sealevel Systems ULTRA COMM+2.LPCI Page
4
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-422/485 input in addition to a 1K ohm pull-up/pull-down combination
that biases the receiver inputs. Headers J1A and J2A 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+2.LPCI adapters are configured in a 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 6 - Headers J1A and J2A, Line Termination