Hi Paul,

I am working on a HOT project. I intend to use a 12C508 with internal
oscillator.

My problem as below.

I have 2 pins of the PICmicro to select the tones. Totally I have 4
sweeps
to generate.

I have to generate the following sweep freq's.

1. 500 Hz to 1200 Hz  - 3 Sec
2. 800 Hz to 970 Hz  - 1 Sec
3. 1200 Hz to 500 Hz  - 1 Sec
4. 2400  to 2850 Hz.  - 0.143 Sec

I have to check the DIP switch change to change the Freq band during my
freq generation. I also have to maintain 15 % duty cycle.

Could you expalin  "phase accumulator" technique in a bit more detail or
if
you can give me code snipped to try it out on a PICmicro it would be
great.
Expecting to finish the project with some help

Thanks for your guidance.

Pailoor


Paul B. Webster VK2BZC wrote:

> Ravi Pailoor wrote:
>
> > For one of my projects,  I need to generate a square wave from 500 Hz
> > to 1200 Hz in steps of around 2 to 3 Hz.
>
>   What is the acceptable jitter?
>
>   If 16µS is acceptable jitter, use a crystal which is any multiple of
> 65536 x 4 = 262144 Hz such as 3.670MHz and I think you can use a "phase
> accumulator" technique where you add the frequency value (in Hertz) to
> a 16-bit accumulator 65536 times per second, the MSB of which is your
> desired square wave.
>
>   A 3.670 MHz crytal would require this to be performed in 14 clock
> cycles (and no other calculations) but if you can tolerate a jitter of
> 32µS or use double the crystal frequency, you have 28 clock cycles in
> which to loop and it becomes much easier.
> --
>   Cheers,
>         Paul B.