Darrel's Multiple Software PWM

[Sean_Goddard]

I have these files somewhere. if I can find them I will post them (if that's OK with Darrel)

[mister_e]

I've uploaded the whole package few weeks ago
http://www.picbasic.co.uk/forum/show...&postcount=210

[passion1]

Steve

Thank you for pointing me in the right direction!

I just realized that Darrel's code is a slow SPWM and cannot handle high frequencies (e.g. up to 20KHz).

I would like to generate two frequencies simultaneously where the one is a
multiple of the other, e.g Freq 1 = 10 kHz, Freq 2 = 20KHz
I do not need to vary the duty cycle. I only need a duty cycle of 50%, thus
either on or off.

Darrel's code would have been perfect if it could handle higher frequencies.

I cannot use the hardware PWM because all PICs with multiple PWM outputs that I know of, share the same timebase.
Thus the frequency must be the same on all the outputs, but the duty cycles are individually controllable. I don't know of a PIC that's an exception

In short, I am looking for a software PWM that is capable of handling 2 different frequencies simultaneously, where each frequency may vary up to 20KHz. I have looked everywhere but could not find any example code to this.

I will appreciate any help or suggestions.

[paul borgmeier]

Are the two fequencies always a factor of 2X apart? (10kHz and 20kHz)
What else does this PIC need to do?
Do the two PWM need to be in phase?

[Sean_Goddard]

PWM and maybe a programmable divider OR a divider and a MUX to select the appropriate frequency multiple.

Whats your application btw please??

[passion1]

Thank you guys.
I got the following clever code from MeLabs support, that solves my problem. It produce simultaneous frequencies of 20KHz, 10KHz, and 5KHz:

DEFINE OSC 20 ' Use a 20MHz crystal for best results

freq_delay VAR WORD

freq_delay = 25 ' 25uS for 20KHz top frequency ((1/20K)/2)
TRISB = %11111000 ' freq pins to outputs

' Output 20KHz on RB0, 10KHz on RB1, 5KHz on RB2
' Adjust freq_delay to compensate for loop overhead
loop:
PAUSEUS freq_delay
PORTB = (PORTB & %00000111) + 1 ' count binary 000 to 111
GOTO loop