[Coco] Re: [Color Computer] CoCo 2 questions.

[Bob Devries]

Sorry to disagree here, but the TCC1000 is a glue chip, that took the place
of several chips on the original coco1 pcb.

----- Original Message -----
From: "Mike Pepe" <lamune at doki-doki.net>
To: <ColorComputer at yahoogroups.com>
Sent: Friday, May 13, 2005 7:35 AM
Subject: [Coco] Re: [Color Computer] CoCo 2 questions.


> Phil,
>
> Phill Harvey-Smith wrote:
> > Hi,
> >
> > Just got myself a cheap, (£4.99) CoCo 2 off ebay, not working at the
> > moment, but I intend to fix that :) I have a couple of questions :
> >
> > 1) It seems very different from the CoCo 1, much more compact, and seems
> >   to have some different chips. Does anyone know where I can get a
> > circuit sheet for this, I have the CoCo 1 tech ref, but this seems to
> > different.
>
> I might have one, I can check, but it would be NTSC not PAL- not much
> difference I would imagine.
>
> > 2) There are a couple of chips with numbers I don't recognise they are :
> >
> > HD61J204P / TCC1000, a 28 pin chip on the bottom left of the board.
>
> That's the BASIC ROM
>
> > SC7331P, a 40 pin chip in the top middle of the board, next to the 6821,
> > this seems to be connected to the keyboard, so I assume it's a PIA, but
> > that's a number I don't recognise.
>
> It's roughly the equivalent of a 6822, which was discontinued and
> replaced with this "custom" part. If it's dead, a 6822 or 6821 can be
used.
>
> > 3) There seem to be some wire links to select between 16K and 64K rams,
> > assuming that I can get some 64K, what type does it need (41464s at a
> > guess) ?
>
> Depends on the board. All can be upgraded with 8 4164 DRAMs. Some can
> take 2 64kx4 chips.
>
> > Also the machine seems to have a 74LS785, rather than a 74LS783, I have
> > tested this in my Dragon test board and it works ok, but wondered what
> > the difference was ?
>
> Functionally identical with the major difference being the 785 supports
> 256 column refresh RAMs (like 4164) whereas the 783 has a 7 bit counter
> and only can refresh 128 column (max) rams.
>
> -Mike
>
>
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