Re: Request a discrete refresh circuit schematic

["Bryan Parkoff" <nospam@nospam.com>]

"Bill Garber" <willy46pa@comcast.net> wrote in message 
J6GdnYNI18fr05HYnZ2dnUVZ_vqdnZ2d@comcast.com">news:J6GdnYNI18fr05HYnZ2dnUVZ_vqdnZ2d@comcast.com...
>
> "Ed Eastman" <noone@nowhere.net> wrote in message
> news:eeh3qo$2s6$1@unlnews.unl.edu...
> : Since there is no A2 hardware forum, I'll post it here...  (Sorry about
> : posting to the emulators group.)
> :
> : I need a circuit to refresh some stand alone ram for a RAM expansion
> : circuit I am designing.  (12M Ram on the IIgs)  I understand the basic
> : theory but I need an actual circuit with real RAM chips to help me
> : visualize the process. I've looked on the internet but the refresh
> : circuit is always glossed over and people are using a memory manger or
> : some such chip that I don't have access to.
> :
> : Would someone please send me a discrete schematic of a refresh circuit
> : on say, a 4 meg bank of RAM?  Or I'd be just as happy with a point to
> : some resources readily available via internet or book reference.
> :
> : I forgot to mention I'd like to use some old 8bit SIMMs I have laying
> : around.  Of course the circuit would be just as easy on a 72 pin simm.
> :
> : Thanxk,
> : Ed
> : eeastmanNO@SPAMgmail.com
>
> Ed,
>
> I sent you a private message. I hope you
> get it, because there is a lot of info in
> there. Let me know.
>
> Bill Garber
> Owner - Garberstreet Enterprizez
> Co-owner - GSE-Reactive.com
> (610)935-7676 (610)329-8996
Hello,

    The problem is that Apple IIgs' motherboard is limited to 8 MB of RAM. 
I doubt when you try to expand RAM to 12 MB.  It may be accessible maximum 8 
MB leaving free 4 MB RAM.  Do you think what you need to modify the logic on 
motherboard to break the limit of 8 MB?
    Think of Apple IIgs ROM 03.  It has 1.25MB built in.  You add 8 MB of 
RAM to be 9.25MB, but it is still accessible to 8 MB.  I wonder.
    Between $80 and $DF banks are for ROM like firmware of TransWarp GS on 
$BC bank and RAM Keeper.

Bryan Parkoff