Chapter 3: Option Selection
To help you locate the jumpers described in this section, refer to Figure 3-2, Option Selection Map at the
end of this section. Operation of the serial communications section is determined by jumper installation as
described in the following paragraphs.
Terminations
A transmission line should be terminated at the receiving end in its characteristic impedance. Installing a
jumper at the locations labeled LDxO and LDxI apply a 120
Ω
load across the transmit/receive input/output
for RS422 operation.
120
Tx+/Rx+
TX-/Rx-
LDxO
Figure 3-1
: Simplified Termination Schematic
In RS422 operations where there are multiple terminals, only the RS422 ports at each end of the network
should have terminating impedance as described above. To so terminate the COM A port, place a jumper
at the location labeled LDAO. To terminate the COM B, COM C, and COM D ports, place jumpers at
locations labeled LDBO, LDCO, and LDDO respectively. Similarly, inputs are terminated at jumpers
labeled LDAI, LDB1, etc.
Also, for RS422 operation, there must be a bias on the Tx+ and Tx- lines. If the card is not to provide that
bias, contact the factory technical support.
Data Cable Wiring
SignalPin Connection
TX+
2
TX-
3
RX+
9
RX-
1
Ground
5
Baud Rate Ranges
The jumpers labeled CLK X1 and CLK X4 provide means to select baud rates in either of two ranges.
When in the "X1" position, the baud rate range is up to 115,200 baud. When in the CLK X4 position, the
baud rate range is 200 to 460,800 baud.
Interrupts
Please note that, in Windows NT, changes must be made to the system registry to support IRQ sharing.
The following is excerpted from "Controlling Multiport Serial I/O Cards" provided by Microsoft in the
Manual PCI-COM-422/4
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