Microchip Technology MA160014 Data Sheet

 2010-2012 Microchip Technology Inc.

DS41412F-page 187

6.

Configure and start the 8-bit TimerX resource:

• Clear the TMRxIF interrupt flag bit of the 

PIR2 or PIR4 register. See 

 below.

• Configure the TxCKPS bits of the TxCON 

register with the Timer prescale value.

• Enable the Timer by setting the TMRxON 

bit of the TxCON register.

7.

Enable PWM output pin:

• Wait until the Timer overflows and the 

TMRxIF bit of the PIR2 or PIR4 register is 
set. See 

 below.

• Enable the CCPx pin output driver by 

clearing the associated TRIS bit.

14.3.3

PWM TIMER RESOURCE

The PWM standard mode makes use of one of the 8-bit
Timer2/4/6 timer resources to specify the PWM period.

Configuring the CxTSEL<1:0> bits in the CCPTMRS0
or CCPTMRS1 register selects which Timer2/4/6 timer
is used.

14.3.4

PWM PERIOD

The PWM period is specified by the PRx register of 8-bit
TimerX. The PWM period can be calculated using the
formula of 

.

When TMRx is equal to PRx, the following three events
occur on the next increment cycle:

• TMRx 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.

14.3.5

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 PRx and TMRx
registers occurs). While using the PWM, the CCPRxH
register is read-only.

 is used to calculate the PWM pulse

width.

 is used to calculate the PWM duty cycle

ratio.

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 TMRx register is concatenated with either
the 2-bit internal system clock (F

OSC

), or two bits of the

prescaler, to create the 10-bit time base. The system
clock is used if the TimerX 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 (see

Note 1: In order to send a complete duty cycle

and period on the first PWM output, the
above steps must be included in the
setup sequence. If it is not critical to start
with a complete PWM signal on the first
output, then step 6 may be ignored.

The Timer postscaler (see 

) is not used in the

determination of the PWM frequency.



 1



 4 T

 







T

OSC

 = 1/F

OSC



   











