Microchip Technology MA300015 Data Sheet

© 2011 Microchip Technology Inc.

DS70150E-page 87

13.4.2

PWM PERIOD

The PWM period is specified by writing to the PRx
register. The PWM period can be calculated using

.

PWM frequency is defined as 1/[PWM period].

When the selected TMRx is equal to its respective
period register, PRx, the following four events occur on
the next increment cycle:

• TMRx is cleared.

• The OCx pin is set.

- Exception 1: If PWM duty cycle is 0x0000, 

the OCx pin will remain low.

- Exception 2: If duty cycle is greater than PRx, 

the pin will remain high.

• The PWM duty cycle is latched from OCxRS into 

OCxR.

• The corresponding timer interrupt flag is set.

See 

 for key PWM period comparisons.

Timer3 is referred to in the figure for clarity. 

PWM Period   = [(PRx) + 1] • 4 • T

OSC

 •

(TMRx Prescale Value)

Period

Duty Cycle

TMR3 = Duty Cycle (OCxR)

TMR3 = Duty Cycle (OCxR)

TMR3 = PR3

T3IF = 1

(Interrupt Flag)

   OCxR = OCxRS

TMR3 = PR3

(Interrupt Flag)

   OCxR = OCxRS

T3IF = 1