[Coco] 1mb and 2mb memory upgrades

[tonym]

I'd be in for two or three 2MB boards.

Tony


---- Original Message ----
From: "Kip Koon" <computerdoc at sc.rr.com>
Sent: 3/14/2015 12:07:22 AM
To: "'CoCoList for Color Computer Enthusiasts'" <coco at maltedmedia.com>
Subject: Re: [Coco] 1mb and 2mb memory upgrades

Hi Al,
Yes, my 512KB Static Ram Memory Upgrade PCB uses 2 - 512KB chips since the data bus is 16 bits.  Why a 16 bit data bus for the add-on memory upgrade PCB since the 6809 is an 8-bit microprocessor? I don't know.  Maybe refreshing the dynamic ram played a part in their decision to make the memory expansion data bus 16 bits.  Two 8-bit data bus memory chips made the design much easier - less chips.  Therefore my 512KB Static Ram Memory Upgrade PCB is actually a 1MB Static Ram Memory PCB with the highest order address line grounded effectively blocking any access to the full 1MB.  Since the Coco 3's 12 pin address header only goes up to 9 bits for the multiplexed address bus, that translates to 9*2 or 18 address bits for a total of 262144 bytes of ram per write enable and 8-bit data bus.  Two write enables and 2 - 8 bit data buses equals 262144*2 = 524288 bytes of ram memory.  And there you have it.  A quick break down of why 2 - 512KB chips are used on my 512KB Static Ram Memory Upgrade PCB.  :)  

Kip Koon
computerdoc at sc.rr.com
http://www.cocopedia.com/wiki/index.php/Kip_Koon


> -----Original Message-----
> From: Coco [mailto:coco-bounces at maltedmedia.com] On Behalf Of Al Hartman
> Sent: Friday, March 13, 2015 1:19 PM
> To: CoCoList for Color Computer Enthusiasts
> Subject: Re: [Coco] 1mb and 2mb memory upgrades
> 
> I was under the impression that the Triad and Kip's new Memory upgrades are actually using larger RAM chips, and only providing 512k
> of the available memory.
> 
> So, except for the new circuitry to provide the access to the additional memory, there should be little additional power draw from a
> 1mb or 2mb board.
> 
> I want a 512k upgrade for my Coco 3, but it's not urgent and if a 2mb board is coming -- I might as well wait and just keep saving my
> money.
> 
> Somewhere I have an unused Dennis Lewandowski 256k upgrade for the Coco 1. I never used it, and I wonder if it's still workable. It's
> just a bunch of chips piggybacked and daisychained with wires. If I come across it, I'll take pictures and post it.
> 
> I have lots of little goodies like this, because I was often checking out possible new products for Spectrum Projects and Zebra Systems.
> 
> -[ Al ]-
> 
> 
> --
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> Coco at maltedmedia.com
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