[Coco] CoCo Internals (was: Coco Sound - Cartridge Input)

[tim lindner]

On Fri, Jan 4, 2019 at 12:08 AM Andrew <keeper63 at cox.net> wrote:
> Without researching it (I may be wrong), did only the SSC use that line?

The Orch-90 cart used it as well. Mono thru the TV, Stereo thru it's own jacks.


> Or what about the Spectrum Analyzer cartridge (how did that work -
> unless I didn't read the schematic properly and that line doesn't bypass
> the DAC)...?

It used audio from the cassette port. Did frequency counting with the
zero crossing circuit.


> ...and did the CoCo 3 have a similar input line from the cartridge
> connector? I didn't check it's service manual to find out.

Yes.


> There was one chip that is the 6821 - plain and simple. But there's a
> second chip that has a different number (don't recall what), but in the
> SM is marked as being a 6821 "select" chip? This is mentioned a couple
> of times in the SM, but it never says what it means by "select", or the
> reason for the different number. Maybe more is said in the datasheet for
> the 6821; I haven't looked.

The difference between the PIAs is the amount of current they can push
thru the output pins. This make the keyboard more reliable.



-- 
--
tim lindner

"Proper User Policy apparently means Simon Says."