[Coco] hardware question - coco3 RAM subsystem

[Mark Marlette]

Stephen,

You will also need a MMU extension, video register and other GIME mirrored functions to get the CoCo to do more than 512k.

CPLD a must, not really but once you have been there, like it sounds you have. There is no looking back. :)

Regards,

Mark
Cloud-9


 
----- Original Message -----
From: "Stephen Adolph" <twospruces at gmail.com>
To: "CoCoList for Color Computer Enthusiasts" <coco at maltedmedia.com>
Sent: Thursday, March 26, 2009 12:38:56 PM GMT -06:00 US/Canada Central
Subject: Re: [Coco] hardware question - coco3 RAM subsystem

Hey thanks for the response and info.

(since reading that video and CPU are muxed on every clock cycle, I
understand better).

Two things are motivating me
1) I want to attempt the 2MB upgrade
2) I already have a custom PCB with CPLD mounted and a 2MB SRAM chip
mounted, from another project.

see comments below.  In general I love to support the people who make
hardware for vintage stuff.  I'll be after cloud nine for the CPU
upgrade.  But in this case I have already invested mega$$ in my Model
100 hardware projects - one of which was an MMU memory system that
mapped 6MB into the M100.



On Thu, Mar 26, 2009 at 1:20 PM, Mike Pepe <lamune at doki-doki.net> wrote:
> Hey Steve,
>
> When you say 2MB I assume you mean 2 megabit meaning they're probably
> 256k x 8 in size? I think that would work out well as you need to make a
> 16 bit wide array to most easily feed the GIME.

I think it is only an 8 bit data bus? ( I see 2 banks of RAM but only
8 bits of bus width to the GIME).

I have a single 2MByte SRAM chip on a board, with a low power CPLD,
running at 3.3 Volts.  Those chips are a little pricey but I got a
whole mess of them on ebay.

This chip is either 8 or 16 bits wide - I'll use it in 8 bit mode
unless I learn that I need 16 bits.

The entire card takes only 6 mA or so at 5V, so it will be very low
power compared to what is there now.  It was designed for the M100.

>
> If all you want is to upgrade a CoCo3 to 512k and you think your time is
> worth more than 40 bucks, go here
>
> http://www.cloud9tech.com/
>
> and click on the hardware tab for the upgrade board. I've bought
> probably 4 of them and they work great.
>

Yes..for all the other upgrades I will go there.  I like the challenge
of making hardware so I will reserve the memory upgrade for myself,
and get everything else from cloud9.

I don't want to make any new PCBs, but as I said I already have this hardware.

This card I have is not much larger than the existing RAM chips, so it
will fit in very nicely.  I'll post photos when done.

cheers Steve

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