[Coco] Re: Color Computer 3 prototype

[jdaggett at gate.net]

Nick

I am convinced that the board has the GIME chip in discrete form. 

One proof is that there is nine (9) 74LS151 chips. These are 8 to 1 
multiplexer ICs. The only reason one would need 9 of them is to 
form the Z-Bus output. 

In conjucntion there are three 4 to 16 decoders. These from the 
lower four bits of th eaddress buss will along with a chip select from 
a PAL will address individual registers in the FF9x block, FFCx 
block and FFDx block. FFAx and FFBx are the pallete rams and 
there are two 74LS189 chips that are 16x4 sram. Two comprises a 
16x8 sram. That handles the MMU ram and another two forms the 
pallette register. 


I think I am within a week of being able to decipher a detailed block 
diagram of the board and what is the GIME. I won't be able to tell 
which individual IC goes to what section though. What I will be able 
to do is suggest a possible start for someone to do a reverse 
engineering of the board. 

james

On 21 Jan 2005 at 16:14, Nickolas Marentes wrote:

From:           	Nickolas Marentes <NickM at qm.qld.gov.au>
To:             	"Coco List (coco at maltedmedia.com)" 
<coco at maltedmedia.com>
Date sent:      	Fri, 21 Jan 2005 16:14:07 +1000
Subject:        	[Coco] Re: Color Computer 3 prototype
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> I wonder if that board is really the CoCo2 Plus (or CoCo
> Deluxe...whatever it was being called). I just don't feel that the
> circuit contains enough to have a GIME.