Specifications

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Note
There is no means to alter the printer port's interrupt, so
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).
Bidirectional Parallel Port Usage
The parallel printer port can be used as a normal AT printer port, or it can be used for general
purpose programmable I/O. By using the port's input and output handshake signals on along
with its 8-bit bidirectional data lines, many types of interfaces for specialized devices can be
created, including writing data to LCD display panels, scanning keyboards, etc.
When configured as a bidirectional data bus, the parallel port cannot be used to support a standard
printer.
Refer to Chapter 3 for typical system software configuration information, and to Chapter 4 for
hardware details regarding nonstandard uses of this interface.
2.4.4 Serial Ports
The board's serial/parallel controller option (U22, U15, U16, U8, and associated circuitry) must
be installed for the serial port function to be available. Two AT (and PC) compatible serial ports
appear at header connectors J2 and J3. Each provides three RS232C output signals and five
RS232C input signals, to facilitate connecting a broad range of serial devices to the Little
Board/286 on either port (see Table 2-13).
Both ports support software selectable standard baud rates up to 19.2K bits/second (limited by the
RS232C drivers), 5-8 data bits, and 1, 1.5, or 2 stop bits. The serial ports appear at the standard
port addresses of 3F8-3FFh (primary port) and 2F8-2FFh (secondary port), using interrupts IRQ4
and IRQ3, respectively.
These two serial ports can be used for connection of printers, modems, terminals, remote hosts, or
other serial devices. The main interface consideration is that the device be RS232C compatible.
Many devices, such as printers and modems, require handshaking in one or both directions.
Consult the documentation of the external serial device for information regarding possible
handshake and other interface considerations.
Support in the ROM-BIOS allows a device connected via one of the board's serial ports to be used
as the system "console" (keyboard and display), as an alternative to the use of a video controller,
monitor, and keyboard. This is further discussed in Chapter 3.
Table 2-13 gives the connector pinout and signal definitions for both J2 and J3. In addition, the
pins to which each signal should be wired for compatibility with the COM port external serial
connectors of PC's (DB25) and AT's (DB9) are also indicated. The pinout of both serial
connectors is such that when direct flat ribbon cable is used between either header and a DB9
connector, the resulting DB9 matches the standard AT serial expansion port connector pinout.