PIC18F47J53 Datasheet, PDF (266/586 Pages) Microchip Technology – 28/44-Pin, High-Performance USB Microcontrollers with nanoWatt XLP Technology

PIC18F47J53 FAMILY
18.4 PWM Mode
In Pulse-Width Modulation (PWM) mode, the CCP4 pin
produces up to a 10-bit resolution PWM output. Since
the CCP4 pin is multiplexed with a PORTB data latch,
the appropriate TRIS bit must be cleared to make the
CCP4 pin an output.
Figure 18-3 shows a simplified block diagram of the
CCP1 module in PWM mode.
For a step-by-step procedure on how to set up the CCP
module for PWM operation, see Section 18.4.3
“Setup for PWM Operation”.
FIGURE 18-3:
SIMPLIFIED PWM BLOCK
DIAGRAM
Duty Cycle Registers
CCP4CON<5:4>
CCPR4L
CCPR4H (Slave)
Comparator
R
TMR2
(Note 1)
S
Comparator
PR2
Clear Timer,
CCP1 pin and
latch D.C.
Q
RC2/CCP1
TRISC<2>
Note 1:
2:
The 8-bit TMR2 value is concatenated with the 2-bit
internal Q clock, or 2 bits of the prescaler, to create
the 10-bit time base.
CCP4 and its appropriate timers are used as an
example. For details on all of the CCP modules and
their timer assignments, see Table 18-2 and
Table 18-3.
A PWM output (Figure 18-4) has a time base (period)
and a time that the output stays high (duty cycle). The
frequency of the PWM is the inverse of the period
(1/period).
FIGURE 18-4:
PWM OUTPUT
Period
Duty Cycle
TMR2 = PR2
TMR2 = Duty Cycle
TMR2 = PR2
18.4.1 PWM PERIOD
The PWM period is specified by writing to the PR2
register. The PWM period can be calculated using the
following formula:
EQUATION 18-1:
PWM Period = [(PR2) + 1] • 4 • TOSC •
(TMR2 Prescale Value)
PWM frequency is defined as 1/[PWM period].
When TMR2 is equal to PR2, the following three events
occur on the next increment cycle:
• TMR2 is cleared
• The CCP4 pin is set
(An exception: If the PWM duty cycle = 0%, the
CCP4 pin will not be set)
• The PWM duty cycle is latched from CCPR4L into
CCPR4H
Note:
The Timer2 postscalers (see Section 14.0
“Timer2 Module”) are not used in the
determination of the PWM frequency. The
postscaler could be used to have a servo
update rate at a different frequency than
the PWM output.
DS39964B-page 266
Preliminary
 2010 Microchip Technology Inc.