Newsgroups: comp.sys.apple2
Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!m.cs.uiuc.edu!ernie!bazyar
From: bazyar@ernie (Jawaid Bazyar)
Subject: Re: I'm wondering if anyone else is interested in the following...
Message-ID: <1991Apr24.171642.4678@m.cs.uiuc.edu>
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Reply-To: bazyar@cs.uiuc.edu (Jawaid Bazyar)
Organization: Mutation Testing Facility, University of Illinois
References: <14942@darkstar.ucsc.edu>
Date: Wed, 24 Apr 91 17:16:42 GMT
Lines: 32

In article <14942@darkstar.ucsc.edu> unknown@ucscb.ucsc.edu (The Unknown User) writes:
>
>	I am planning on designing a memory board that will take 4
>megabyte SIMMs. This is a memory board for the GS that is.
[...]
>	If someone is interested in this, please E-MAIL me about it.
>From what Todd Whisell has told me, apparently it will only be DMA to 4 
>megs (plus whatever's on the motherboard), so a greater amount of DMA ability 
>isn't a good reason to get one of these... 

    Good luck. You're going to have to expend quite a bit of effort to 
get this working.  I thought about supporting 4meg SIMMs when I designed
my RAM card (built, but not yet working- noise problems).  The memory
slot has an MSIZE signal to choose between 256K and 1M banks.  This
goes back to the FPI (CYA) to tell it how to mux the addresses for the
card.  To support 4Meg SIMMs (and making it DMA compatible) would require
latching the bank address during certain clock cycles, and combining that
with a recombined address (also constructed over different clock cycles)
to produce an address, which would then have to be re-muxed.  In short,
what you'd need would be a new DRAM controller on the board.  Stick to
1M SIMMs and your life is much easier.

>-- 
>/unknown@ucscb.ucsc.edu Apple IIGS Forever! WANT ULTIMA VI //e or GS?-mail me.\
>\CHEAP CDs info-mail me. McIntosh Junior:  The Power to Crush the Other Kids. /


--
Jawaid Bazyar               |  "Twenty seven faces- with their eyes turned to
Senior/Computer Engineering |    the sky. I have got a camera, and an airtight
bazyar@cs.uiuc.edu          |     alibi.."
   Apple II Forever!        |  I need a job... Be priviliged to pay me! :-)
