Chapter 3
Configuring Your SCXI Hardware and Software
3-50
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SCXI-1200 Module
The SCXI-1200 controls the operation of and digitizes the conditioned
analog signals from other SCXI modules. The SCXI-1200 has eight analog
input channels, which can be configured as eight SE or four DIFF; a 12-bit
successive-approximation ADC; two 12-bit DACs with voltage outputs; 24
lines of TTL-compatible digital I/O; and 16-bit counter/timer channels for
timing I/O.
You can use the SCXI-1200 module in two types of configurations:
•
connecting the SCXI-1200 module directly to the parallel port of the
computer
•
connecting the SCXI-1200 to the parallel connector of the SCXI-2000
or SCXI-2400 for connection to RS-232 or RS-485 serial ports.
The SCXI-1200 complies with the IEEE 1284 parallel port standard. This
IEEE protocol supports three different parallel port types—the original
Centronics or unidirectional port for printers, the PS/2 type bidirectional
port, and the 386-SL Enhanced Parallel Port (EPP).
Parallel Port Interface
If you plan to connect the SCXI-1200 directly to the parallel port of your
computer, read this section carefully.
An IBM-compatible computer can support up to three parallel printer ports,
which are designated LPT1, LPT2, and LPT3. Each port uses three
consecutive I/O addresses. When you power up your system, DOS assigns
the printer ports to the logical LPT designations in the following
order—LPT1, LPT2, and LPT3. The starting addresses of the parallel
printer ports, in the order assigned to LPT designations, are 3BC, 378,
and 278 hex. Therefore, if you have installed all three ports, 3BC hex is
LPT1, 378 hex is LPT2, and 278 hex is LPT3. If you have not installed port
3BC hex, port 378 hex becomes LPT1 and port 278 hex becomes LPT2.
If only one parallel port is present, it is LPT1.
The SCXI-1200 can use the parallel port hardware interrupts for
interrupt-driven data acquisition. Interrupt levels 7 and 5 are commonly
used for parallel ports. Refer to your parallel port reference manual for
details about interrupt selection.
When you use the SCXI-1200, you must know which port and interrupt
channel is being used. If you use the SCXI-1200 with NI-DAQ software,
however, you select the port and interrupt at configuration time.
