PIC18F45K80-I Datasheet, PDF (262/622 Pages) Microchip Technology – 28/40/44/64-Pin, Enhanced Flash Microcontrollers with ECAN and nanoWatt XLP Technology

PIC18F66K80 FAMILY
19.4 PWM Mode
In Pulse-Width Modulation (PWM) mode, the CCPx pin
produces up to a 10-bit resolution PWM output. Since
the CCPx pin is multiplexed with a PORTC or PORTB
data latch, the appropriate TRIS bit must be cleared to
make the CCPx pin an output.
Note:
Clearing the CCPxCON register will force
the corresponding CCPx output latch
(depending on device configuration) to the
default low level. This is not the PORTx
I/O data latch.
Figure 19-3 shows a simplified block diagram of the
CCPx module in PWM mode.
For a step-by-step procedure on how to set up the CCP
module for PWM operation, see Section 19.4.3
“Setup for PWM Operation”.
FIGURE 19-3:
SIMPLIFIED PWM BLOCK
DIAGRAM
Duty Cycle Registers
CCPR4L
CCP4CON<5:4>
CCPR4H (Slave)
Comparator
TMR2
(Note 1)
R
Q
S
RC2/CCP1
Comparator
PR2
Clear Timer,
CCP1 Pin and
Latch D.C.
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 19-2.
A PWM output (Figure 19-4) 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 19-4:
PWM OUTPUT
Period
Duty Cycle
TMR2 = PR2
TMR2 = Duty Cycle
TMR2 = PR2
19.4.1 PWM PERIOD
The PWM period is specified by writing to the PR2
register. The PWM period can be calculated using the
following formula:
EQUATION 19-1:
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 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 15.0 “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.
DS39977F-page 262
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