PIC Code - PWM (50% Duty Cycle)

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devonsc

Joined: 30 Nov 2004
Posts: 116
Helped: 1

30 Nov 2004 20:15 PIC Code - PWM (50% Duty Cycle)

Hi there,

I'm a newbie in using PIC microcontroller and would like to ask something regarding the duty cycle of a PWM coding.

If its not too much trouble, can anyone briefly explain how do I determine the duty cycle of a PWM duty cycle in the coding? Is it true that 255 (decimal) is equivalent to 100% duty cycle while 0 (decimal) is equivalent to 0% duty cycle? If this is right, does it mean that I should write:

movlw d'127'

for a duty cycle of 50%? Advice needed..Please? Thanks in advance..

nicleo

Joined: 06 Sep 2004
Posts: 717
Helped: 60

01 Dec 2004 3:23 PIC Code - PWM (50% Duty Cycle)

Which PIC microcontroller that you're using? Some PIC microcontrollers, e.g. PIC16F877A, has built-in PWM module.

The following article might help:
http://ww1.microchip.com/downloads/en/DeviceDoc/31014a.pdf

Here has many links on using PWM of PIC microcontroller:
http://www.microchip.com/stellent/idcplg?IdcService=SS_GET_PAGE&nodeId=1490&filterID=409

IanP

Joined: 05 Oct 2004
Posts: 6492
Helped: 1542
Location: West Coast

01 Dec 2004 3:43 Re: PIC Code - PWM (50% Duty Cycle)

Your guess is correct: for 50% the number is 127d.

devonsc

Joined: 30 Nov 2004
Posts: 116
Helped: 1

02 Dec 2004 12:45 Re: PIC Code - PWM (50% Duty Cycle)

Thanks a lot.

By the way, I'm using PIC 16F876.

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btbass

Joined: 20 Jul 2001
Posts: 1187
Helped: 113
Location: Oberon

04 Dec 2004 0:03 PIC Code - PWM (50% Duty Cycle)

The PIC16f876 has 2 PWM modules with a resolution of 10bits. So your period could have a count of 1024. The data sheet gives formulas for calculating the duty cycle based on the frequency and resolution.