Card Setup
OMG-ULTRA-485-PCI
Page
4
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 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.
1 2 3 4
ON
OFF
5
P P T L L
Figure 4 - Switch SW1, Line Termination
