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

Mike Pepe lamune at doki-doki.net
Fri May 13 12:09:23 EDT 2005

Phill Harvey-Smith wrote:

> Humm I get a forbidden error, though I can get to the other two files in
> http://www.doki-doki.net/~lamune/temp/
> file permissions on coco2b.tif perhaps ?

Yeah, oops... try that again please.

> Right, though I meant 8x4164 :) 

Actually you can indeed put 8 41256 chips in a CoCo 1/2 with a 74LS785. 
A 41256 ram also has 256 refresh cycles. There was a circuit provided in 
Rainbow ages ago that let you have 4 banks of 64k by installing 41256 
DRAMs and a LS785...

...Would like to find that article again...

> Indeed, for £4.99, remembering that CoCos where a lot less common here in the UK.


> Ahh, so effectivley it and the SAM become a chipset that can't operate
> independent of each other (well you could use the sam on it's own but not the
> 6847TI), also I suppose iliminating the latch means 1 less chip so drives down
> production costs when you are making thousands of them.

The SAM/VDG connection isn't really relevant in the CoCo/Dragon world 
because of course both chips are always present. The internal latch is 
absolutely a cheap-factor enhancement.

> Heheheh, well I suppose if they mentioned it, people without it would also want
> lower case etc, and perhaps they didn't want to offer an upgrade path :)

Well the T1 chip is not drop-in compatible with the regular 6847- 
presumably though you can bypass the TTL latch and make a minor mod or 
two to the older board to drop in a T1. It's on my list of things to try.

> Though I do seem to remember that someone mentioned a mod that you could do to
> allow you to use an external character rom to get lower case, shame that's not
> on the web somewhere.

Yes, that's also on my list. Check the 6847 data sheet if you can find 
one, it shows you how to add the external CG ROM. It only takes one 
counter TTL chip and a ROM.

> Hehehe, well I don't think either of my CoCos, or any of my Dragons for that
> matter has not been modded in some way :), even if it's just to upgrade them to
> the latest version of basic, and max 64K ram :)

That's about all you can ask for!

Anyway, hope that helps

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