[Coco] [Color Computer] updated wikipedia article

[jdaggett at gate.net]

Mike 

One glaring error that I see is in the following paragraph:

Due to limitations in 40 pin packaging, the SAM contains a duplicate of the VDG's 
internal 12 bit address counter. Normally this counter's settings are set to duplicate 
the VDG's display mode. However this is not required and results in the creation of 
some new display modes not possible when the VDG is used in a system alone.

The linear address counter for video memory in the SAM chip is a 16 bit counter 
and not a 12 bit counter. Setting the F0-F6 flip flops allows the video ram to be set 
on any 512 byte boundary within the 64K memory map. This difers from the 
MC6847. The VDG supplies the lower 12 bits of address and has to rely on external 
address decode logic to be able to map where video ram was located in 8K 
boundaries. Due to the increase capabilites of the SAM chip's linear address 
generator for video memory, the SAM chip inconjucntion with the VDG allowed 
increase of three semi graphics video modes.  

Also someone unfamiliar with the Coco line would think that the MC6883/74LS783 
and the MC6847 were developed exclusively for the Coco. This inference would not 
be true. Each chip can operate with any 8 bit computer on its own and not with 
exclusively with the MC6809/MC6809E.  Furthermore the MC6883 and the 
74LS783 are the same chip. The SAM chip is LSTTL logic and was done on a 
bipolar line as opposed to the VDG chip which is High Density NMOS and done on 
a MOS line. I am not sure that this is the "gospel" as to how it got two part numbers 
but one possibility is related to which camp the part went to. If sold under the LSTTL 
catalog it would have the 74LS783. Conversely if sold under the Motorola Computer 
Products it had the MC6883 label. I vaguely remember around the 1980 time frame 
that there was a growing number of parts that carried dual numbers and  there was 
a cleanup or consoldation of internal/external documentation. 

Finally the ACVC or GIME is woefully breif if one is trying to give a technical 
description of the hardware. The GIME chip is not 100% backwards compatible. It is 
not just an integration of the MC6883 and the MC6847. It is by far a more complex 
IC than the previous pair and a design of its own from the ground up.  

james

On 16 Nov 2005 at 19:52, Mike Pepe wrote:

To:             	ColorComputer at yahoogroups.com
From:           	Mike Pepe <lamune at doki-doki.net>
Date sent:      	Wed, 16 Nov 2005 19:52:32 -0500
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> Hi listers,
> 
> I was working on a "CoCo Tech" web page, but when I saw the entry for
> the Atari 8 bit machines on wikipedia I decided to integrate my work
> there instead.
> 
> http://en.wikipedia.org/wiki/TRS-80_Color_Computer
> 
> now includes a lot of hardware information, though I'm not sure if
> that would really be of interest to most people.
> 
> Comments are welcome.
> 
> -Mike
> 
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