[Coco] Re: CoCo Orchestra-90

[Torsten Dittel]

Andrew schrieb:
 
> I did a quick scan-thru of the O-90CC manual, and something I found
> which seemed disappointing was no mention of how (or if it were
> possible) to control the cartridge from BASIC, ML or OS-9.
 
> Does anyone know if this is possible? Is there an "unravelled"-style
> book or document describing how to do this? Did Rainbow or another
> magazine ever publish anything about such access?

The O-90CC's hardware is nothing more than two 8-bit
Digital-Analog-Converters (DACs). You can take a multimeter, POKE some
values between 0 and 255 to the memory locations

&HFF7A (left channel) 
&HFF7B (right channel)

and measure how the voltage changes. If you connect the Pak to your
amplifier and to the changes fast enough (e.g. a sine wave) or a
digitized (sampled) voice, you would listen it (you should use assembler
for doing so).

If you need multiple voices (e.g. 4-part harmony) you have to do
something called time multiplexing or you have to add the samples and
divide the result by the number of voices.

Hope that helps to get an idea.

Torsten

PS: it should be possible to use parts of the Paks ROM routines to
output something from BASIC but I guess the ROM isn't documented.