Impulse 7402 - Manual (Page 8)

Card Setup
Sealevel Systems ULTRA COMM+422.PCI Page 5
Line Termination
Typically, each end of the RS-485 bus must have line terminating resistors
(RS-422 terminates 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 biases the receiver inputs. Headers J1A – J4A 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.PCI
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 6 - Headers J1A – J4A, Line Termination