Datasheet

© 2010 Microchip Technology Inc. DS70139G-page 89
dsPIC30F2011/2012/3012/3013
12.4.2 PWM PERIOD
The PWM period is specified by writing to the PRx
register. The PWM period can be calculated using
Equation 12-1.
EQUATION 12-1:
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 remains low.
- Exception 2: If duty cycle is greater than PRx,
the pin remains high.
• The PWM duty cycle is latched from OCxRS into
OCxR.
• The corresponding timer interrupt flag is set.
See Figure 12-2 for key PWM period comparisons.
Timer3 is referred to in Figure 12-2 for clarity.
FIGURE 12-2: PWM OUTPUT TIMING
PWM period = [(PRx) + 1] • 4 • Tosc •
(TMRx prescale value)
Period
Duty Cycle
TMR3 = Duty Cycle
TMR3 = Duty Cycle
TMR3 = PR3
T3IF = 1
(Interrupt Flag)
OCxR = OCxRS
TMR3 = PR3
(Interrupt Flag)
OCxR = OCxRS
T3IF = 1
(OCxR)
(OCxR)