Apple II Computer Info
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### Created : Friday, February 7, 1997 Modified: Friday, February 7, 1997
### File Type: "TEXT" File Creator: "LMAN"
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Newsgroups: comp.sys.apple2
Subject: Re: Hacking GS memory card?
Date: Fri, 7 Feb 1997 20:57:58 +1300
Organization: Empsoft
Lines: 34
NNTP-Posting-Host: dempson.actrix.gen.nz
X-Newsreader: MacSOUP 2.2b6
> I've been poking around Apple's 1meg memory board for the //gs, trying
> to increase it's memory capacity... hopefully to 4meg. Anybody have
> any experience/knowledge in gs memory handling?
Yep. I have the IIgs hardware reference, and I'm quite familiar with
how standard memory cards are implemented (the more oddball ones are
somewhat of a mystery).
> I desolered the eight dram chips already on the board and ran some wires
> to a socketed 256k SIMM on a proto-board. This tested ok. I then tacked a
> wire to the unused FRA9 (pin3) line, ran that through the same type of
> inverter/resistor (as the other address lines are handled) and brought it
> to A9 of a 1meg simm. It would only give me 768k.d
You have missed an important step. There is a pin on the memory slot
which tells the motherboard what size of RAM is installed on the card.
The Apple IIgs Memory Expansion Card is set for 256KB rows, so the
motherboard doesn't use FRA9, and the row address lines decode into
multiples of 256KB.
If the appropriate pin is set for 1MB RAM then FRA9 contains the next
multiplexed address bit, and the row address lines decode into multiples
of 1MB.
The pin in question is called MSIZE. It is pin 27 on the slot
connector. It is unconnected for a card with 256KB rows, connected to
ground for a card with 1MB rows.
--
David Empson
Apple II Computer Technical Information : Apple II Family Hardware Info
ftp://ground.ecn.uiowa.edu/2/apple2/miscinfo/hardware : May 2001 : 206 of 572
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