[sdiy] Roland DCOs

[Dave Manley]

Here's a labled pic of the voice ckt I posted to AH at the time:

http://www.sonic.net/~dlmanley/p08VoiceLabeled.jpg

Unfortunately, the pics (I believe taken by Stephen Johnson) were a bit 
blurry and made it impossible to dig all the details out, but what Eric 
describes is essentially correct (except there's one dsPIC per two 
voices).  Looking at the pics again, the clock osc labeling is not clear 
enough to make out, but looks like 4?00, so perhaps it is 40MHz.

-Dave



Eric Brombaugh wrote:
>
> I seem to recall a similar discussion on AH back when the first 
> internal photos of the DSI P08 came out a few months ago. From what I 
> recall of that thread, the P08 uses a bunch of the motor control dsPIC 
> chips. There's one dsPIC per voice controlling a CM3396-like chip. The 
> motor control variety has a bunch of nice PWM outputs that can 
> presumably provide the digital divider output, plus there's an 
> 8-channel SPI DAC being used for the numerous voltage control points 
> on the '3396. To top it all off there's another dsPIC that talks to 
> the keyboard, panel controls & MIDI, coordinating the behavior of the 
> per-voice dsPICs.
>
> At the time, I sat down and figured out the frequency resolution you'd 
> get from the dsPIC dividers and it looked pretty decent. Here's what I 
> wrote then:
>
> -----------------
> I was curious about which dsPIC was being used. Notice that it's the 
> 'MC' version - that probably means that he's using the motor control 
> PWM channels to generate the waveshaper drive pulses.
>
> The motor control time base has 15-bit resolution with a 1/4/16/64x 
> prescaler - that should give plenty of frequency accuracy. I've no 
> idea what the dsPIC clock rate is, but assuming it's running near it's 
> maximum, 40MHz is a good ballpark. Given that, you get the following 
> resolution at the various prescaler settings:
>
> 1:1 - Range is 2441Hz and up. Resolution is ~0.15Hz at 2441, ~2.3Hz @ 
> 10kHz.
> 1:4 - Bottom of range is 610Hz. Resolution there is 0.03Hz, 0.6Hz at 
> 2.4kHz.
> 1:16 - Bottom of range is 152Hz. Resolution is 0.009Hz, 0.15Hz at 600Hz
> 1:64 - Bottom of range is 38Hz. Resolution is 0.002Hz, 0.04Hz at 150Hz
>
> Those resolutions give about 1/10 cent accuracy at the low ends of the 
> range and 1/2 cent at 4x higher. Not too bad.
>
> Not sure what the overall frequency range of the '08 is, but if it 
> goes lower than 38Hz then the dsPIC is may be running slower than 40MHz.
> -----------------
>
> Eric
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