Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!usc!apple!dlyons
From: dlyons@Apple.COM (David Lyons)
Newsgroups: comp.sys.apple
Subject: Re: Reading the 80 column screen
Message-ID: <36476@apple.Apple.COM>
Date: 14 Nov 89 20:34:27 GMT
References: <1989Nov3.044252.8555@polyslo.CalPoly.EDU> <11@marilyn.UUCP>
Organization: Apple Computer Inc, Cupertino, CA
Lines: 25

In article <11@marilyn.UUCP> shawn@marilyn.UUCP (Shawn P. Stanley) writes:
>[...]
>Use a routine called BASCALC at $FBC1 to get the line address into $28-$29.
>Do this by loading the line number into the A-register before calling $FBC1.
>If the horizontal position is odd (I believe; maybe it's even), add 4 to
>location $29.  Then, divide the horizontal position by two and load with
>Y-register indirectly through $28-$29:
[code sample omitted]

Adding $400 to the pointer will move you from main text page 1 ($0400-$07FF) to
main text page 2 ($0800-$0BFF).  This won't help a whole lot, since half the
columns of the 80-column text screen are storedin *auxiliary* page 1, at
$0400-$07FF in auxiliary memory ("bank 1").  If you're writing code for use
on a GS only, you can address $01xxxx any way you want--for 8-bit Apple II
machines in general, you need to mess with some $C0xx softswitches (80STORE,
PAGE1, and PAGE2), as shown in the Technical Note excerpt I posted last week.
-- 

 --Dave Lyons, Apple Computer, Inc.          |   DAL Systems
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