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© Sealevel Systems, Inc.
7101 Manual | SL9160 9/2021
CARD SETUP, CONTINUED
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. Header E4 allows customization of this interface to specific
requirements. Each jumper position corresponds to a specific portion of the interface. If multiple
ULTRA
530.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 7 - Headers E3, Line Termination