PIC18F47J53 Datasheet, PDF (267/586 Pages) Microchip Technology – 28/44-Pin, High-Performance USB Microcontrollers with nanoWatt XLP Technology

PIC18F47J53 FAMILY
18.4.2 PWM DUTY CYCLE
The PWM duty cycle is specified by writing to the
CCPR4L register and to the CCP4CON<5:4> bits. Up
to 10-bit resolution is available. The CCPR4L contains
the eight MSbs and the CCP4CON<5:4> contains the
two LSbs. This 10-bit value is represented by
CCPR4L:CCP4CON<5:4>. The following equation is
used to calculate the PWM duty cycle in time:
EQUATION 18-2:
PWM Duty Cycle = (CCPR4L:CCP4CON<5:4>) •
TOSC • (TMR2 Prescale Value)
CCPR4L and CCP4CON<5:4> can be written to at any
time, but the duty cycle value is not latched into
CCPR4H until after a match between PR2 and TMR2
occurs (that is, the period is complete). In PWM mode,
CCPR4H is a read-only register.
The CCPR4H register and a two-bit internal latch are
used to double-buffer the PWM duty cycle. This
double-buffering is essential for glitchless PWM
operation.
When the CCPR4H and two-bit latch match TMR2,
concatenated with an internal two-bit Q clock or two
bits of the TMR2 prescaler, the CCP4 pin is cleared.
The maximum PWM resolution (bits) for a given PWM
frequency is given by the equation:
EQUATION 18-3:
PWM Resolution (max)
=
log


F--F--P^-O--W^{--S---CM---}
-------l--o---g----_--2----_-------bits
Note:
If the PWM duty cycle value is longer than
the PWM period, the CCP4 pin will not be
cleared.
TABLE 18-5: EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 40 MHz
PWM Frequency
2.44 kHz 9.77 kHz 39.06 kHz 156.25 kHz 312.50 kHz 416.67 kHz
Timer Prescaler (1, 4, 16)
16
4
1
1
1
1
PR2 Value
FFh
FFh
FFh
3Fh
1Fh
17h
Maximum Resolution (bits)
14
12
10
8
7
6.58
18.4.3 SETUP FOR PWM OPERATION
To configure the CCP module for PWM operation:
1. Set the PWM period by writing to the PR2
register.
2. Set the PWM duty cycle by writing to the
CCPR4L register and CCP4CON<5:4> bits.
3. Make the CCP4 pin an output by clearing the
appropriate TRIS bit.
4. Set the TMR2 prescale value, then enable
Timer2 by writing to T2CON.
5. Configure the CCP4 module for PWM operation.
 2010 Microchip Technology Inc.
Preliminary
DS39964B-page 267