"Interfacing the IBM PC parallel printer port" - читать интересную книгу автора (Stewart Z.)


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==== Version 0.96 9/1/94 Zhahai Stewart [email protected]

Interfacing the IBM PC Parallel Printer Port

1. Overview

This document is called an FAQ because it answers many commonly asked
questions about the IBM parallel port, but it is formatted more as a brief
tutorial. Read it twice before asking for more info; some stuff comes
late.

Most of this I puzzled out for myself from various documention and
experiences. The IBM documentation has some errors; I've had to cross
correlate various sources including schematics to get a consistent and
workable picture. Since the first version, others have contributed
information, proofreading, and suggestions (see acknowledgements).

Starting with the original IBM PC, IBM defined a standard parallel printer
port which has become very widespread. This port uses a female DB-25S
connector on the computer, and a special male DB-25P to Centronics male 36
pin "IBM Printer cable" is used to connect to standard Centronics parallel
printers. This DB-25 connector is possible because about half of the
Centronics pins carry just electrical ground.

The original definition was embodied in the "IBM Printer Adaptor", and the
"IBM Monochrome Display and Printer Adaptor" cards.

2. Conventions used in this document.

An electrical "high" (on a pin or line) is TTL high, +2.4 to +5 volts.
An electrical "low" is TTL low, 0 to +0.8 volts.

A data high is a 1, a data low is a 0.

The connection between data (eg: a register bit) and pins is direct if a
data 1 is associated with an electical TTL high, and inverted if data 1
is associated with TTL low. An overall connection (data to TTL to data)
is considered direct if outputing a 1 produces a 1 on input at the other
end, or inverted if outputting a 1 produces a 0 on the other end.

Pin labels, like "-Strobe" or "+Busy", are as defined by the printers and
by IBM. The prefix "-" (or draw a line over the name) implies that the
signal is "active low"; that is, that when the signal is in its active state
when electically low. The "+" prefix means "active high", just the opposite.