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© Sealevel Systems, Inc.
7105-DB9 Manual | SL9053 9/2021
CARD SETUP, CONTINUED
Address and IRQ selection
The
ULTRA 485.OPTO22
is automatically assigned resources by your motherboard BIOS and or the
operating system.
Adding or removing other hardware or moving the adapter to a different PCI slot may change the
assignment of I/O addresses and IRQs.
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. Switch SW1 allows customization of this interface to specific
requirements. Each switch position corresponds to a specific portion of the interface. If multiple
ULTRA 485.OPTO22 adapters are configured in an RS-485 network, only the boards on each end should
have switches T, P & P ON. Refer to the following table for each position’s opera
tion:
Name
Function
T
Adds or removes the 120 ohm termination.
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).
L
Connects the TX+ to RX+ for RS-485 two-wire operation.
L
Connects the TX- to RX- for RS-485 two-wire operation.
Figure 4 - Switch SW1, Line Termination
1 2 3 4
ON
OFF
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P P T L L
