Herbert Graf wrote:
> I'm using a dsPIC30F2010. I've configured the PWM for free running mode,
> no post scale, no pre scale, no dead time (yet), nothing fancy.
>
> I load PTPER with 99 (comes from a macro, value confirmed with the
> ICD2), and then load PDC1 with whatever I want.
>
> I put a scope to the PWM pin and voila, a duty cycle of half what I
> expect!??!

First, which PWM generator are you using?  The one that is most like other
PICs is called the "output compare" module.  The "motor control PWM" is a
new and different beast.  I have used both of these, and never encountered
such a symptom.  There were some flakys is early versions of the '2010
output compare module, but those have all been fixed.  Anyway, those had to
do with spurious pulses caused by unrelated events.

The motor control PWM module has a lot of options.  I'm guessing you are
using it and have the mode set incorrectly in one of the many control
registers.  A factor of two sounds suspiciously like you are thinking single
slope and it's doing dual slope, or the other way around.  I vaguely
remember that there was a factor of two difference between some of the
modes.

Do you really need all the flexibility of the motor control PWM, or will the
simpler output compare module do it?

Unlike other PICs where everything you need is in the data sheet, on the
dsPIC you need their equivalent of the midrange reference manual.  It's
called "dsPIC30F Family Reference Manual".  Unfortunately there isn't a
single DS number for this manual because they gave each chapter a different
one.

You need to read section 15, "Motor Control PWM" (if that's what you're
using) completely and thoroughly.  Actually, I've found it's useful to skim
a section once to get the general flavor, then read it carefully word for
word.  Only then are you ready to write code.


*****************************************************************
Embed Inc, embedded system specialists in Littleton Massachusetts
(978) 742-9014, http://www.embedinc.com
_______________________________________________
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist