Specifications

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4.5.2 Parallel Printer Port
The parallel printer port on the Little Board/286 is functionally identical to that found in a
standard AT with one exception: its eight data lines can be put in a mode in which they are used to
read the state of the printer port data lines (rather than being write only). Because you can use this
port as a two-way 8-bit bus, it can be very valuable in custom applications.
All data and interface control signals are TTL compatible, and the port can be utilized as a set of
general purpose digital I/O signals if it is not required for use with a parallel printer. There are
many non-printer applications for this port, including using it to control an LCD display panel,
scanning keyboards, sensing switches, and even interfacing with optically-isolated I/O modules.
Jumper options allow the port to be configured as either the primary or secondary printer device,
which differ in the particular I/O port base address (378h or 278h) used. Refer to Chapter 2 for
jumpering information.
Note
There is no means to alter the printer port's interrupt.
Although its I/O port address can be set to the standard LPT1
or LPT2 values, its interrupt remains at IRQ7. DOS does not
use the interrupt, while some printer port control software
does (such as print spoolers).
The parallel port hardware can be disabled by the board's ROM-BIOS at powerup or reset, based
on a parameter in the board's configuration EEPROM. The port enable/disable parameter is
normally set using the Ampro SETUP configuration utility (see Chapter 3). When the port is
disabled in this manner, its I/O port addresses and system interrupt becomes available on the AT
Expansion Bus for other devices in the system.
Bidirectional Printer Port Use
A unique "Printer Output Enable" (POE) signal, which can be used to control the data direction of
the printer port's eight data lines, is provided at the board's printer interface connector (J3 pin 26).
This signal is pulled low by a 1K resistor, R32, which normally keeps the printer port data lines in
the output direction. To use the printer port data lines bidirectionally, you must remove R32.
Note that with R32 removed, the POE signal must be grounded for normal parallel printer port
use.
A convenient way to generate the port output enable signal is simple to tie the POE signal (J3 pin
26) to one of the parallel port's output control lines (-STROBE, -AUTOFD, -INIT, or -SEL IN).
Ampro recommends using -INIT. Whichever line you use, be sure that your software controls that
line in such a way that you get the data direction you want.
In addition to the bidirectional use of the eight data lines, the four control lines (-STROBE, -
AUTOFD, -INIT, and -SEL IN) can be used as general purpose output lines. Similarly, the five
status lines (-ERROR, SEL OUT, PAPER EMPTY, -ACK, and BUSY) can be used as general
purpose input lines.