[Coco] [Color Computer] updated wikipedia article

Thu Nov 17 19:07:39 EST 2005

Perhaps I misinterpreted what exactly was the glaring error.  Are you saying
that the writer was mistaken not simply in claiming that the SAM has 12 address
bits when instead it has 16, but was more broadly mistaken in characterizing
there as being 12 bits in the SAM that correspond in the usual display modes to
12 analogous bits in the VDG?  I had not previously heard that claim, but
assumed it to be correct since it is certainly the case that certain VDG and SAM
input values "go together" in producing the common display modes, and that you
get unusual display modes by mixing the values in other than the common
combinations.

Art

On Thu, 17 Nov 2005 jdaggett at gate.net wrote:

> Art 
> 
> To me it appears to point someone unknowing of the Coco Internals 
> as thinking the two are near identical. At least that is my perception. 
> Then I maybe out of bounds from the rest of the group.
> 
> james
> 
> On 17 Nov 2005 at 15:07, Arthur Flexser wrote:
> 
> Date sent:      	Thu, 17 Nov 2005 15:07:37 -0500 (EST)
> From:           	Arthur Flexser <flexser at fiu.edu>
> To:             	CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> Subject:        	Re: [Coco] [Color Computer] updated wikipedia article
> Send reply to:  	CoCoList for Color Computer Enthusiasts <coco at maltedmedia.com>
> 	<mailto:coco-request at maltedmedia.com?subject=unsubscribe>
> 	<mailto:coco-request at maltedmedia.com?subject=subscribe>
> 
> > I'm not really seeing the "glaring" error.  To say that the SAM
> > contains a duplicate of the VDG's 12 bit address counter does not deny
> > that the SAM might have more address bits available as well, just that
> > 12 of its bits would normally duplicate the VDG's 12 bits.
> > 
> > Art
> > 
> > On Thu, 17 Nov 2005 jdaggett at gate.net wrote:
> > 
> > > 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
> > > Copies to:      	Subject:        	[Coco] [Color Computer] updated
> > > wikipedia article Send reply to:  	CoCoList for Color Computer
> > > Enthusiasts <coco at maltedmedia.com>
> > > 	<mailto:coco-request at maltedmedia.com?subject=unsubscribe>
> > > 	<mailto:coco-request at maltedmedia.com?subject=subscribe>
> > > 
> > > > 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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