Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!ll-xn!mit-eddie!bbn!rochester!cornell!batcomputer!braner
From: braner@batcomputer.tn.cornell.edu (braner)
Newsgroups: comp.sys.atari.st
Subject: Re: how do I print-screen (Alt<help>) on Epson LQ-500/800?
Message-ID: <4675@batcomputer.tn.cornell.edu>
Date: 3 May 88 20:56:54 GMT
References: <8804281839.AA00314@ucbvax.Berkeley.EDU> <476@philmds.UUCP>
Reply-To: braner@tcgould.tn.cornell.edu (braner)
Organization: Cornell Theory Center, Cornell University, Ithaca NY
Lines: 18
Summary: Actually it is much simpler

In article <476@philmds.UUCP> leo@philmds.UUCP (L.J.M. de Wit) writes:
>    1) Alter the bios, as follows...  (much follows)

- actually replacing the screen dump routine is rather simple, since there
is a vector to it (albeit not well publicized).  The LONG at the address
$502 points to the standard routine, called by both the Alt-Help mechanism
and the XBIOS Scrdmp() function (in turn called by various paint programs).
You can simply replace the contents of that vector with the address of your
custom screen dumper, which should be a Terminate-and-stay-resident TOS
program you can place in the auto folder.  You have to do something to avoid
reentry of the actual dump code if one presses Alt-help while the dump
is in progress.  Also, you should provide for abortion on request or if
the printer does not respond.

I have actually written such a beast for my printer (an Apple Dot Matrix,
no kiddin!) (which is really a modified NEC 8023), so if there is much demand
I can post the source code.  Warning: it is in assembly language.

- Moshe Braner