[Coco] CoCo 3 512k SRAM Upgrade Z-BUSS DEMULTIPLEX

[coco at yourdvd.net]

OKAY, I THINK I MAY HAVE SOLVED THIS. FIRST THIS IS MY SUGGESTION FOR
DEMULTIPLEXING THE Z-BUS:





              ----------------
              |              |
RAS*----------|>             |
              |           OUT|
              |          8..0|}-----------}TO STATIC RAM
              |              |             ADDRESS 17..9
              | NEGATIVE-EDGE|
              | TRIGGERED    |
              | LATCH        |
              |              |
              |              |
              |              |
Z-BUS 8..0----|              |
              |              |
              ----------------






              ----------------
              |              |
CAS*----------|>             |
              |           OUT|
              |          8..0|}-----------}TO STATIC RAM
              |              |             ADDRESS 8..0
              | NEGATIVE-EDGE|
              | TRIGGERED    |
              | LATCH        |
              |              |
              |              |
              |              |
Z-BUS 8..0----|              |
              |              |
              ----------------


NEXT I WILL INCLUDE WHAT I THINK WILL BE A FUNCTIONAL REMAINDER OF THE
CIRCUIT. -R


> -------- Original Message --------

> Subject: Re: [Coco] CoCo 3 512k SRAM Upgrade (Renamed Thread)

> From: coco at yourdvd.net

> Date: Sun, April 22, 2007 7:36 am

> To: CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>

> 

> I have the service manual in my hands. What I'll do is make a truth

> table from the access diagrams and then we can work from that. The way

> memory access is performed is different than I originally thought - I

> had thought about using a 512Kx8 static RAM because I thought the we0

> and 1 signals functioned like r/w* lines, but NOT QUITE :-) -r >

> -------- Original Message -------- > Subject: [Coco] CoCo 3 512k SRAM

> Upgrade (Renamed Thread) > From: coco at yourdvd.net > Date: Sun, April

> 22, 2007 7:24 am > To: CoCoList for Color Computer Enthusiasts  > > 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 follows: 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 years...) 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 > > 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 > > >

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