PIC18F4321 Datasheet, PDF (147/396 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with 10-Bit A/D and nanoWatt Technology

PIC18F4321 FAMILY
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.
When the CCPRxH and 2-bit latch match TMR2,
concatenated with an internal 2-bit Q clock or 2 bits of
the TMR2 prescaler, the CCPx pin is cleared.
The maximum PWM resolution (bits) for a given PWM
frequency is given by the equation:
EQUATION 15-3:
PWM Resolution (max)
=
log
⎛
⎝
F--F--P^-O--W^{--S---CM---⎠⎞}
----------------------------- bits
log (2)
Note:
If the PWM duty cycle value is longer than
the PWM period, the CCPx pin will not be
cleared.
TABLE 15-4: 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)
10
10
10
8
7
6.58
15.4.3 PWM AUTO-SHUTDOWN
(CCP1 ONLY)
The PWM auto-shutdown features of the Enhanced CCP
module are also available to CCP1 in 28-pin devices. The
operation of this feature is discussed in detail in
Section 16.4.7 “Enhanced PWM Auto-Shutdown”.
Auto-shutdown features are not available for CCP2.
15.4.4 SETUP FOR PWM OPERATION
The following steps should be taken when configuring
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
CCPRxL register and CCPxCON<5:4> bits.
3. Make the CCPx 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 CCPx module for PWM operation.
© 2007 Microchip Technology Inc.
Preliminary
DS39689E-page 145