PIC16F722A Datasheet, PDF (130/284 Pages) Microchip Technology – 28-Pin Flash Microcontrollers with nanoWatt XLP Technology

PIC16F/LF722A/723A
15.3.2 PWM PERIOD
The PWM period is specified by the PR2 register of
Timer2. The PWM period can be calculated using the
formula of Equation 15-1.
EQUATION 15-1: PWM PERIOD
PWM Period = PR2 + 1  4  TOSC 
(TMR2 Prescale Value)
Note: TOSC = 1/FOSC
When TMR2 is equal to PR2, the following three events
occur on the next increment cycle:
• TMR2 is cleared
• The CCPx pin is set. (Exception: If the PWM duty
cycle = 0%, the pin will not be set.)
• The PWM duty cycle is latched from CCPRxL into
CCPRxH.
Note:
The Timer2 postscaler (refer to
Section 13.1 “Timer2 Operation”) is not
used in the determination of the PWM
frequency.
15.3.3 PWM DUTY CYCLE
The PWM duty cycle is specified by writing a 10-bit value
to multiple registers: CCPRxL register and DCxB<1:0>
bits of the CCPxCON register. The CCPRxL contains
the eight MSbs and the DCxB<1:0> bits of the
CCPxCON register contain the two LSbs. CCPRxL and
DCxB<1:0> bits of the CCPxCON register can be written
to at any time. The duty cycle value is not latched into
CCPRxH until after the period completes (i.e., a match
between PR2 and TMR2 registers occurs). While using
the PWM, the CCPRxH register is read-only.
Equation 15-2 is used to calculate the PWM pulse
width.
Equation 15-3 is used to calculate the PWM duty cycle
ratio.
EQUATION 15-2: PULSE WIDTH
Pulse Width = CCPRxL:CCPxCON<5:4> 
TOSC  (TMR2 Prescale Value)
Note: TOSC = 1/FOSC
EQUATION 15-3: DUTY CYCLE RATIO
Duty Cycle Ratio = ^---C----C----P----R---x---L4---:-_-C-P---C-R---P-2---x--+-C----O1----_^{N----<----5---:--4--->-----}
The CCPRxH register and a 2-bit internal latch are
used to double buffer the PWM duty cycle. This double
buffering is essential for glitchless PWM operation.
The 8-bit timer TMR2 register is concatenated with
either the 2-bit internal system clock (FOSC), or 2 bits of
the prescaler, to create the 10-bit time base. The system
clock is used if the Timer2 prescaler is set to 1:1.
When the 10-bit time base matches the CCPRxH and
2-bit latch, then the CCPx pin is cleared (refer to
Figure 15-3).
DS41417A-page 130
 2010 Microchip Technology Inc.