[Coco] Coco Sound - Cartridge Input

[Andrew]

I was recently looking over the service manual for the CoCo 2, and was 
reading about the fact that there was a sound input line from the 
cartridge connector (IIRC, it bypassed the DAC).

Without researching it (I may be wrong), did only the SSC use that line? 
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)...?

...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.

I just recently purchased and received a set of several SN76489 chips; 
it seems strange to me that Tandy/RS neglected the sound capabilities of 
the CoCo so much, and never saw fit to add something like this chip in. 
It would likely have been a cheap addition, even back then - it was 
certainly used on plenty of other machines of the era.

I also wished they had done something like dual processors or similar, 
though that would have boosted the complexity and cost of the system 
significantly for the time - so it's understandable that they didn't.

Oh - and one other thing if anyone can answer: What is the difference 
between the two PIA chips on the CoCo (2? not sure if same on the 3)?

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.

Lastly - I know of a source here in Phoenix which has tubes upon tubes 
of 6821, and a particular variant of the 6809 (unfortunately, not the 
68B09E) - among other vintage parts.

It's Apache Reclamation and Electronics, if anyone cares to know. I've 
purchased small numbers of these and other parts from them, but I know 
for certain they have a ton more stock of these parts (seen 'em with my 
eyes). If I had the money I'd purchase the entire stock, but they know 
what they have...

Over last weekend I grabbed some MOS parts (some RIOT chips and some 
TIAs - I think those were the parts - plus a particular 65xx CPU 
variant); got those and some 40 pin wire-wrap sockets...

--
Andrew L. Ayers
Glendale, Arizona
https://github.com/andrew-ayers