Scott Dattalo wrote:

> If I understand you correctly, you basically want a 16-level pwm output
> with a frequency somewhere between 20-30 khz from a 16c84(?) running off
> of a 4Mhz crystal. If you do the arithmetic, that comes out to between
> 50 - 33 instruction cycles per pulse. (4Mhz / 4 / 20khz) That's tough!

You're telling me! I'm using a 12c508.

> You might wish to check out my single-cycle resolution 256 level pwm or
> 32 level pwm:
>
> http://www.interstice.com/~sdattalo/technical/software/pic/pwm.txt
> http://www.interstice.com/~sdattalo/technical/software/pic/pwm256.txt

Thanks, I'm going there now...

> However, it might be more feasible to implement an intertwined
> isochronous routine (iir - okay I made it up). Do you remember Dwayne

I thought that an isochronous approach should work.

> Reid's pulse sampling problem a couple of months ago? I don't have time
> to elaborate right now, but maybe someone else can (Dwayne?). But
> basically, you can get a resolution of about 3 instruction cycles with
> the algorithm. So in your case, you could have 16 levels * 3
> instructions/level for 48 instructions per pulse. This also gives you 16
> instructions per pulse for other processing (like sampling Vds and
> determining the next pulse width).

Just over 20kHz! Dwayne! Give us you input!

I'll post a shematic of the circuit I built later.

--
Friendly Regards

Tjaart van der Walt
mailto:tjaart@wasp.co.za

|--------------------------------------------------|
|                WASP International                |
|R&D Engineer : GSM peripheral services development|
|--------------------------------------------------|
|SMS mailto: tjaart@sms.wasp.co.za  (160 chars max)|
|     http://www.wasp.co.za/~tjaart/index.html     |
|Voice: +27-(0)11-622-8686  Fax: +27-(0)11-622-8973|
|          WGS-84 : 26¡10.52'S 28¡06.19'E          |
|--------------------------------------------------|