[Coco] CoCo 1 vs 2 detection (was 86-87 GIME chip detect challenge)

[Darren A]

On Sat, Dec 7, 2013 at 4:33 PM, John Kowalski wrote:

>
> I'm not sure there would be a way to detect the SALT chip, unless
> there were some way to send a signal through it and measure how long
> it takes for it to make it to the other side.
> (Going on the assumption that the SALT is faster than the (741?), a
> signal coming out of the SALT should stabilize/change state faster
> than it would on the 741)
>
>
I think I may have found a way to detect a CoCo1 vs a CoCo2.  At least it
worked in the very limited test of the two machines I have.  Rather than
look for the SALT chip it tries to detect if the machine has the custom
integrated DAC chip.

The theory is that the custom chip in the CoCo 2 does not allow
bidirectional flow through the analog switch, whereas the MC14529B used in
the CoCo 1 does.  The test selects the cassette port as the audio source
and then toggles the single-bit sound output while looking for a change on
the cassette data input.  If the predicted change is seen then it would
appear that bidirectional flow through the switch is occuring and the
machine is a CoCo 1.

Should anyone care to try it and report their findings, below is the Basic
program I used to perform the test:

10 POKE &HFF23,&H33
20 POKE &HFF22,&HFA
30 POKE &HFF23,&H37
40 AUDIO ON
50 POKE &HFF22,0
60 A=PEEK(&HFF20) AND 1
70 POKE &HFF22,2
80 B=PEEK(&HFF20) AND 1
90 AUDIO OFF
100 PRINT "THIS APPEARS TO BE A COCO";(A<>B)+2

Darren