Modifying Darrel's SSPWM resolution?

[retepsnikrep]

This is probably a question for Darrel.

Anyway i'm using his excellent SSPWM to generate a 2khz pwm output on a 16F88 pic running at 8mhz.

The 1% Duty resolution available as standard works fine.
But can that be increased to 0.1% resolution? Or perhaps 0.5% resolution.

What would I need to change? I see DutyCycle is a byte variable so that needs to be a word if DutyCycle was going to be expanded to 1000 units. It looks like simply a matter of the maths to calculate the TMR1 duty periods but that's not my strong point

http://www.pbpgroup.com/modules/wfse...d.php?fileid=3

Thanks Peter

[retepsnikrep]

Still looking for a bit of advice/guidance re this if possible please.

[Darrel Taylor]

The CalcSPWM: routine calculates the prescaler and ON/OFF times for the PWM.
Then the Timer interrupts do the rest.

You can calculate those times any way you want.
SSPWM calculates for different OSC frequencies, PWM frequencies and dutycycles.
But if you know the OSC and PWM frequency ahead of time, it will be easier for you to do the math.

[retepsnikrep]

In my application the osc is always 8mhz and the frequency is always 2khz, the duty changes from 10-90%.
Your routine works very well I just want to try and increase the resolution to 0.1%

[retepsnikrep]

I'm going to try using a few different values for the duty and get my software to display your calculated values for T1CON, TICKS, TMR1_ON_TICKS, TMR1_OFF_TICKS. Then I will use TICKS & T1CON as constants and remove all the calculation stuff does that sound reasonable? My maths & pic knowledge is not good enough to see how all your calculation routines work

I'll just leave the final duty calculation part in

W1 = Ticks * DutyCycle ' Calc # of Ticks for ON and OFF periods
TMR1_ON_TICKS = div32 100
TMR1_OFF_TICKS = Ticks - TMR1_ON_TICKS

[retepsnikrep]

I tinkered around and found that with my 8mhz int clock and 2khz pwm the prescaler was being set to 1 and ticks was 1000 per cycle. 50% duty Time on/off was 500 ticks each. This suggests that resolution can be increased to 0.1% by changing DutyCycle to a word variable and using 500 instead of 50 to represent 50% duty. I have adjsted the calculation so it now ranges from 0-1000 in steps of 1 instead of steps of 10. I also removed all the calculation routines as ticks are now known as is prescaler etc. That save quite a few bytes as well

Darrel any comments?

Peter