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Address and IRQ selection
The OMG-ULTRA-485-PCI is automatically assigned resources by your motherboard BIOS. Only the I/O address
may be modified by the user.
Adding or removing other hardware 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 OMG-ULTRA-485-PCI 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 operation:
Name
T
P
P
L
L
OMG-ULTRA-485-PCI
Adds or removes the 120 ohm termination.
Adds or removes the 1K ohm pull-down resistor in the
RS-422/RS-485 receiver circuit (Receive data only).
Adds or removes the 1K ohm pull-up resistor in the RS-422/RS-
485 receiver circuit (Receive data only).
Connects the TX+ to RX+ for RS-485 two-wire operation.
Connects the TX- to RX- for RS-485 two-wire operation.
P P T L L
ON
OFF
1 2 3 4
Figure 4 - Switch SW1, Line Termination
Function
5
Card Setup
Page 4
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