********************************************************
** **
** Preliminary Documentation for BakLPT **
** A Turbo Pascal 4 unit to allow Background printing **
** Copyright (c) 1988, Richard S. Sadowsky **
** **
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Version: Alpha test version .6
Date : 8/3/88

BakLPT is a Turbo Pascal 4 unit that allows you to buffer the output to the
Lst device so it can be printed in the background while your application
continues to to process other things. The buffer may be up to 65521
bytes large, and it is declared on the heap. The BakLPT unit maintains
source compatability with the Turbo Pascal Printer unit, and the public
domain LPT Printer replacemnent unit.

Add BakLPT to your USES statement. Be sure to remove Printer or LPT if
they are included in the USES statement. This is the simplest way to
add background printing. By default, a 65521 byte print queue will be set
up on the heap, and all output to the Lst device is automatically placed
in it. At certain intervals, a "background" routine in BakLPT will send
characters from the queue out to the printer while allowing foreground
processing to continue (see Technical Notes below for an explanation of this
"Background" processing).

While there are many advanced features to BakLPT, here are the default
conditions:

FilterPrtSc = FALSE - While Queue is active, PrtSc's will be ignored.

QueueEnabled = TRUE - By default background printing is on.

QueueSize = 65521 - Biggest possible print queue (Current Limitations).

TICKS_TO_WAIT
= 18 - approximately 1 second intervals

CHARS_PER = 80 - send out 80 chars per interval

LPT Number = LPT1 - by default, BakLPT assumes LPT1

UserExitFunc = NONE - BakLPT will wait until buffer empties to exit.
See sample program TBakLPT for a more useful
UserExitFunc.

UserErrorFunc
= NONE - No int 17h error handler installed.


Each of these will be explained in detail (someday).

Current Limitations:

Maximum Queue Buffer size is 65521. This holds 1092 lines of 60
character lines, which is about 16 1/2 pages (at 66 lines per page).
These averages are VERY conservative and you will get more lines and
pages in most real world conditions since the average number of characters
per line is well under the 60 used above.

Do not attempt to use AssignQue on any text file other than the Lst
variable declared in BakLPT. Only one background device is currently
supported.

The UserErrorFunc is called from a hardware ISR, so user beware (will
elaborate later).

Requires the TPInt unit of Turbo Professional 4 (version 4.03 used here).

Turbo Professional 4 is a registered trademark of Sunny Hill Software,
used under license to TurboPower Software.

Turbo Pascal, Turbo Pascal Database Toolbox, Turbo Pascal Editor Toolbox,
and Sidekick are trademarks of Borland International.


Technical Notes:
Just guess for now.

For now, you're on your own from here. See sample program and source for
more info, and stay tuned for new docs Real_Soon_Now.