I've done a fair amount of playing around with PIC16F876's. They
have two built in PWM generators. You set the overall carrier
frequency by writing to a register and then control duty cycle as
you need it. Turns out to be very low overhead.

Hope this helps.
Bruce/ND8I


"xpyttl" wrote in message
...
I'm pretty disappointed at the amount of flame this posting generated.

snip

Secondly the shape of the waveform is an issue. It's real easy to
generate
square waves from the PIC, but in most cases, these will generate lots of
spurious output. Depending on the application and the sort of encoding
you
will use, you will need to come up with nice sine waves. There really are
3
ways to do this ... in many applications you can simply get away with a
good
low pass filter between the PIC and the radio. This will take a bunch of
tweaking, though, and you will need a good scope, and preferably a
spectrum
analyzer to get it right. You can also generate the sine wave by having
the
PIC output the sine wave using pulse width modulation and a little
filtering. In my experience, you can get extremely good sine waves this
way, BUT the PIC is 100% dedicated to the task, which means your data
rates
will need to be low. The third approach is to build an oscillator that
you
can control with the PIC. Given that you will probably need only two
frequencies, this may not be such a bad approach.

snip