[Coco] [Color Computer] Re: POKE 65495,0

[Roger Merchberger]

Rumor has it that James Diffendaffer may have mentioned these words:

> >> Could it even be that different production runs of the SAM have
> >> different behaviors?
> >>
> >> JCE
> >>
> >
> >There was a second generation of the SAM chip called 74LS785 that I
> >think appeared in the
> >Coco2. One of its main features was to extend the refresh counter from
> >7 bits to 8 bits. This
> >allowed the usage of 64Kx1 dram chips. Since I don't have a spec sheet
> >on the 74LS785, so
> >I can't verify that any other functions have changed. From what I have
> >read the 74LS785 is
> >pin for pin compatible with the 74LS783/MC6883.
> >
> >james

I'm pretty sure that it was pin-compatible, but IIRC, there was a non-CoCo2 
mode that gave bankswitching capacity to the memory, and could be used to 
access up to 256K RAM, thru the use of 64Kx4 RAMs...

I had a HotCoCo with an article on using that SAM to upgrade the RAM to 
128K/256K w/a piggyback chip mod... but it's been a long time.

IIRC, the article started out something like "Yes, Virginia, you *can* have 
a 256K CoCo2"... and was in an issue around Christmastime.... possibly 
around '85-ish???

>Actually, I think the newer SAM included a built in latch to reduce
>the motherboard parts count.  I don't think the pinout would change
>much but it would function differently.

I don't *think* so, but again, my memory's rather rusty, as at the time, I 
didn't have $$$ for memory, let alone the SAM upgrade... and by the time I 
did have the money, it went into a shiny new CoCo3. ;-)

Laterz,
Roger "Merch" Merchberger

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