[Coco] CoCo 3 512k SRAM Upgrade (Renamed Thread)

coco at yourdvd.net coco at yourdvd.net
Sun Apr 22 10:24:03 EDT 2007

To Sylvain Rousseau:

I've renamed this thread. I have been looking into your schematic. Now,
from a quick research of the G.I.M.E. I find that a write cycle is as
The G.I.M.E. writes data by BYTE via the we0* or we1* 256k bank selects.
Whilst a read cycle is as follows:
The G.I.M.E. reads data by WORD, 8 bits via cas low followed by latching
the next 8-bits on cas rise and reading it from the latch. (I am using
''WORD'' to represent 16-bits, but it's had so many meanings over the

This will help later on in the day as I work on this.

Anyway, your schematic indicates that you are using negative-edge
triggered latches to demultiplex the z-bus. If this is the case, the
inversion of the ras and cas prior to entering the latches should be
removed. However, I need to find the CoCo 3 timing diagrams, if I had
those, I could solve this in a few hours. Are they online? Perhaps a
copy of the CoCo 3 Tech Ref Manual and/or service manual - if anyone
knows of a readily available download of these, I could solve this in a
couple of hours. I work best from truth tables and timing diagrams
rather than schematics.

Theoretically, during a read cycle, both we0 and we1 should be high, but
if there is the slightest chance that this isn't the case, ANDing the
two signals cannot be used to generate the *we signal. But I need to go
search for the timing diagrams.

Any info anyone might have would be appreciated, because CoCo 3 RAM
access is actually amazing that it even works considering one byte of
the word is latched then fed to the gime and finally to the cpu -
propagation delay from hades, I would think...

I'll keep digging - rob

> -------- Original Message --------
> Subject: Re: [Coco] Re : Re : FREE Services For Members Of The CoCoList
> at Malted Media
> From: coco at yourdvd.net
> Date: Sun, April 22, 2007 5:33 am
> To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> I see what I believe may be some potential problems with the schematic
> but before I go and make a fool of myself, I am going to go fetch the
> data sheet for the sram and examine the gime memory timings. I'll get
> back to you in a few hours. -rob > -------- Original Message --------
> > Subject: [Coco] Re : Re : FREE Services For Members Of The CoCoList
> at > Malted Media > From: Sylvain Rousseau  > Date: Sat, April 21,
> 2007 4:22 pm > To: CoCoList for Color Computer Enthusiasts  > > Yes,
> Mr. Merchberger host it for we at this address: >
> http://zmerch.30below.com/coco/coco3sram.pdf Thank you again Mr. >
> Merchberger. Sylvain ----- Message initial ---- De : Mark Marlette ? >
> : coco at maltedmedia.com Envoy? le : vendredi 20 avril 2007, 13 h 16 min
> > 11 s Objet : Re: [Coco] Re : FREE Services For Members Of The
> CoCoList > at Malted Media IIRC there were some level problems in your
> circuit. I > think you posted a .jpg of it. I looked at it quickly.
> Don't totally > remember. Working other designs and sometimes they all
> run together. > Heck maybe it was my levels that were off.... :) Mark
> Quoting > coco at yourdvd.net: > What 512k static ram are you using? the
> first to > hit the scene were > semistatic requiring something like an
> 8ms? > refresh or so (these were > hitachi). The current ones are
> fully > static. The 4464 used in the 128k > machine use a
> bidirectional i/o > line like the static rams. The 41256 > has a
> seperate din and dout > line but these are shorted together in the >
> coco 3 memory circuit. > did you account for the 256k bank switch? > >
> if all else fails you > can make one of these: > >
> ftp://ftp.maltedmedia.com/coco/TUTORIALS/How_To_Upgrade_To_512k_Without_A_Commercial_Memory_Board.zip
> > > D?couvrez ce qui fait jaser les gens ! Visitez les groupes de >
> l'heure sur Yahoo! Qu?bec Groupes. http://cf.groups.yahoo.com/ -- Coco
> > mailing list Coco at maltedmedia.com >
> http://five.pairlist.net/mailman/listinfo/coco<hr>-- Coco mailing list Coco at maltedmedia.com
> http://five.pairlist.net/mailman/listinfo/coco

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