[sdiy] DCO theory

[GothGeek Sysadmin]

I'll probably be wearing my dunce cap after this one but the ongoing
conversation on building a cheap microcontroller based synth has gotten
me thinking and confused at the same time.

Exactly how do the Roland style DCO's work?

I assumed that they just converted a pulse train into a square wave
and then mutilated in analog from there to the few waveforms they
offer ( speaking from the viewpoint of a Juno6/60/206 owner ).

I in fact have a tube of Scenic SX28's I've been meaning to play with in
just this application.  The timing on these is tight enough that I, perhaps
erroneously, have been thinking of using a few in just this way.  My
thinking is with this chip since its timing is tight enough I would just
lower the clock frequency enough to make normal instruction delay a useful
constant, generate a few pulse streams on the 4 pins of Port A, and use B
and C for inputting 14bit data and an address.
These chips are so cheap tho that even just spitting out a single pulse
stream would be cost effective. I picked these up at under $1ea as they
are still labeled Scenix and not Ubicom.

Is my basic understanding of (Roland) DCO's correct at least or are there
18hundred different ways  of making a DCO.

Thanks!

-- 
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 - Tom Arnold -       When I was small, I was in love,                  - 
 - Sysabend   -       In love with everything.                          -
 - CareTaker  -       And now there's only you...                       - 
 --------------         -- Thomas Dolby, "Cloudburst At Shingle Street" -