[sdiy] DsPIC timer issue when used as DCO!

[Colin f]

> > 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