Subject: Re: 1meg cards for the //e
Newsgroups: comp.sys.apple2.programmer
From: dempson@actrix.gen.nz (David Empson)
Date: Sat, 29 May 1999 00:08:50 +1200
Message-ID: <1dsjfh1.1gf0yseme55l4N@dempson.actrix.gen.nz>
References: <373A5843.4A4BF5BA@insolwwb.net> <19990527192520.08829.00009663@ng-ch1.aol.com>
Organization: Empsoft
X-Newsreader: MacSOUP 2.3
NNTP-Posting-Host: 202.49.157.176
X-Original-NNTP-Posting-Host: 202.49.157.176
X-Trace: 29 May 1999 00:05:57 NZST, 202.49.157.176
Lines: 43
Path: lobby!newstf02.news.aol.com!portc02.blue.aol.com!howland.erols.net!newspeer.monmouth.com!newsfeed.clear.net.nz!usenet.net.nz!news.iprolink.co.nz!news.actrix.gen.nz!dempson



BluPhoenyx <bluphoenyx@aol.com> wrote:

> There were a couple of vendors. I don't know if all of them used the same
> methods, but Applied engineering's method is this.

The competitor (whose name I forget) is apparently identical, except
they use $C071 for the bank select register.

> You place a value between $00-$0f here then access the aux memory as normal.

Note that this includes the language card areas as well as the main 48K
section.  The AUXZPSTACK switch selects between main and auxiliary
memory for the zero page, stack and language card memory areas, and the
bank select register for the auxiliary memory card determines which 64K
bank will be accessed in these areas.

This is rather tricky to manage, so most programs just waste the extra
16K of RAM and limit themselves to the main 48K bank (at least the
$0200-$BFFF area).

As far as I know, the 80-column and double hi-res video buffers only
exist in bank 0 of the card, but I'm not sure whether the 80STORE and
PAGE2 softswitch combination always access this bank or the currently
selected bank.  (Does anyone else know this detail?)

> The Apple slot card is different though. I don't have any info on it.

It isn't bank switched, and you cannot execute code directly out of the
RAM on these cards.  It uses a one-byte window into the RAM, with a
three byte address register.  The address is automatically incremented
whenever you read or write a byte through the window, hence the "slinky"
nickname (it slinks through memory as you access it).

The officially supported method of accessing the RAM on these cards is
through SmartPort calls (reading or writing an arbitrary number of bytes
from or to an arbitrary location in the card).  You can also use them as
a simple RAM disk (supported automatically by ProDOS - no need to patch
anything, because the card has firmware which includes a ProDOS driver).

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand