[sdiy] DsPIC timer issue when used as DCO!

[karl dalen]

Ok, i buy you argument around the core not being reset!
... But only to 5/24! :)

Regards
KD

--- Den fre 2009-12-11 skrev Colin f <colin at colinfraser.com>:

> Från: Colin f <colin at colinfraser.com>
> Ämne: RE: [sdiy] DsPIC timer issue when used as DCO!
> Till: synth-diy at dropmix.xs4all.nl
> Datum: fredag 11 december 2009 16.24
>  
> > > The waveshaper on the 3396 (and presumably the
> 397) 'folds 
> > over' the 
> > > top of  the wave once it reaches the upper
> limit.
> > 
> > No it does not, the folding takes action at +2.5V if
> +12v 
> > vcc, then continues into saturation to create very
> narrow 
> > clipped triangle, have look in the 3396 datasheet
> Colin if 
> > you dont beleve me.
> 
> >From the datasheet:
> "The waveform shaper operates as follows: From 0 to 5/24
> Vcc
> (+2.5v for Vcc = +12v), the convertor output increases
> minimum to
> maximum; from 5/24 Vcc to 5/12 Vcc (+5.0v for Vcc = +12v),
> the
> output decreases from maximum back to minimum; and beyond
> 5/12
> Vcc, the converter output remains at minimum."
> 
> So the saw core rises from 0 to 5v, causing the output
> waveshape for a
> triangle to rise from 0 to maximum, then return to
> minimum.
> 
> The saw core is not being reset, so the waveshaper output
> stays at minimum.
> That is a -ve DC level, so the high pass filtering in the
> output decoupling
> causes the very slow rising ramp you see.
> 
> > > Which brings us back to a timer error.
> > 
> > Sorry, no!
> 
> Sorry, yes ;-)
> 
> Cheers,
> Colin f
> 
> 
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