Page 3-1
Manual 00650-521-1
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
S
load
across the input for RS422 mode. Similarly, installing a jumper at the location labeled
TERMOUT applies 120
S
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. PCI-COM422/485 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 PCI-COM422/485 by the BIOS or Operating System. Alternately, in Windows
95/98/NT the Device Manager can be used. The PCI-COM422/485 is 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.
