Impulse 7204 User Manual
Page 8
Card
Setup
Sealevel Systems ULTRA 485+2.PCI Page
5
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 485+2.PCI 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