Chapter 3: Option Selection
Four configuration options are determined by jumper position as described in the following paragraphs.
Locations of the jumpers are shown in Figure 3-1, Option Selection Map.
422/485
This jumper selects either RS422 or RS485 communications mode.
Termination and Bias
A transmission line should be terminated at the receiving end in its characteristic impedance in order to
avoid “ringing”. Installing a jumper at the location labeled TERMIN applies a 120
Ω
load across the input
for RS422 mode. Similarly, installing a jumper at the location labeled TERMOUT applies 120
Ω
across
the transmit/receive input/output for RS485 operation.
In RS485 operations, where there are multiple terminals, only the RS485 ports at each end of the
network should have terminating resistors as described above. Also, for RS485 operation, there must
be a bias on the RX+ and RX- lines. The 422/485 feature provides this bias.
Baud Rate
The x1/x4 jumper selects either the standard 1.8432MHz clock or 7.3728MHz clock for input to the
UART. The x4 position provides capability for baud rates up to 460,800 KHz.
Interrupts
The IRQ number is assigned by the system. Use PCIFind.EXE to determine the IRQ that was assigned
to the card by the BIOS or Operating System. Alternately, in Windows 95/98/NT the Device Manager
can be used. The cardis listed under the Data Acquisition class. Selecting the card, clicking
Properties
,
then selecting the
Resources
tab will show the base address and IRQ assigned to the card.
Manual PCI-COM-1S
10
