still don't have solution!!!

[texas5]

hi.please help me.i still can't generate my 120khz pwm using pic16f877a.the maximum that i can get is 50khz using hpwm.and 80khz using my own modification pwm(high--puase---low---pause).pleaseeeeeee....help me....

[Acetronics2]

Hi,

... use a 40 Mhz clock !!! ... Pic 18 F xxxx !!!

or a dedicated chip ...

Alain

[skimask]

hi.please help me.i still can't generate my 120khz pwm using pic16f877a.the maximum that i can get is 50khz using hpwm.and 80khz using my own modification pwm(high--puase---low---pause).pleaseeeeeee....help me....

With what code are you trying to generate this 120khz?
I don't see anything either...

[Macgman2000]

Why not just use an LM324 quad opamp. Set up a couple in a feedback oscillator at the frequency of your choice. Run the output of the oscillator (triangle wave) into a third gate as a comparator. From the pic all you need is a couple of resistors to set your DC level at the right place to slice a 50% duty cycle. Easy....you can turn it on and off when ever you want.

Nick

[rmteo]

You will not get 120KHz - the closest is 125KHz. Assuming a clock of 8MHz, this will give you 125KHz on CCP1 (RC2) with a PIC1F877A.

TRISC = 0  'PORTC all outputs
PR2 = 15  'Load Period Register
CCPR1L = 8  'Set 50% duty cycle
CCP1CON = %1100  'PWM mode
T2CON.2 = 1  'Start TIMER2

[skimask]

hi.please help me.i still can't generate my 120khz pwm using pic16f877a.the maximum that i can get is 50khz using hpwm.and 80khz using my own modification pwm(high--puase---low---pause).pleaseeeeeee....help me....

Come to think of it...we've already been over this!!!
If you check one of your other threads, I've already shown that you can generate 120khz using a 'non-standard' crystal.

[ardhuru]

Right, as Skimask says. Check up TipsTricks_41214A.pdf on the Microchip site and scroll down to the X10 carrier generation bit.

Regards,

Anand

[rmteo]

Yes, he can get 120KHz with a standard 12MHz crystal and setting PR2 = 24. I think his problem is that he does not seem to be able to get more than 50KHz with HPWM. It may be a PBP thing, I don't know, that is why I suggested setting up the HPWM manually. With a 8Mhz clock, you can get up to 500MHz PWM, albeit with little to no resolution on the duty cycle.

[skimask]

Yes, he can get 120KHz with a standard 12MHz crystal and setting PR2 = 24.

I don't remember the PR2 value, but I got the same thing using a 9.6Mhz crystal.
Your solution is better though...standard crystal and supported by PBP.

I think his problem is that he does not seem to be able to get more than 50KHz with HPWM. It may be a PBP thing, I don't know

PBP itself won't allow over 32Khz unless using LONG variables (PBPL 2.50), then you can (in theory) get 2Ghz out it...obviously won't happen...or will it? (see below or above whichever)
He's trying to do a square wave manually (bit high, wait, bit low, wait, repeat), bit bang the pins.

that is why I suggested setting up the HPWM manually. With a 8Mhz clock, you can get up to 500MHz PWM, albeit with little to no resolution on the duty cycle.

WOW! 500MHZ from 8MHZ! I want your chip!

[rmteo]

Here is a scope trace of 500KHz HPWM using a 8MHz clock:

Horizontal is 500ns/division, Vertical is 2V/division.

[skimask]

With a 8Mhz clock, you can get up to 500MHz PWM, albeit with little to no resolution on the duty cycle.

post #8

[rmteo]

OK, here is a brain teaser for you. With an 8MHz clock on a PIC16/18, what is the maximum frequency HPWM that can be achieved, and how would you do it (in terms of register values for CCPR1L and PR2)?
Hint: the answer is in the scope trace above.

[rmteo]

post #8

mea culpa. Should have been 500KHz.