PIC16F628-20P Datasheet, PDF (66/170 Pages) Microchip Technology – FLASH-Based 8-Bit CMOS Microcontroller

PIC16F62X
11.3 PWM Mode
In Pulse Width Modulation (PWM) mode, the CCP1 pin
produces up to a 10-bit resolution PWM output. Since
the CCP1 pin is multiplexed with the PORTB data latch,
the TRISB<3> bit must be cleared to make the CCP1
pin an output.
Note:
Clearing the CCP1CON register will force
the CCP1 PWM output latch to the default
low level. This is not the PORTB I/O data
latch.
Figure 11-2 shows a simplified block diagram of the
CCP module in PWM mode.
For a step-by-step procedure on how to set up the CCP
module for PWM operation, see Section 11.3.3.
FIGURE 11-2:
SIMPLIFIED PWM BLOCK
DIAGRAM
Duty cycle registers
CCPR1L
CCP1CON<5:4>
CCPR1H (Slave)
Comparator
TMR2
(Note 1)
RQ
S
RB3/CCP1
Comparator
PR2
Clear Timer,
CCP1 pin and
latch D.C.
TRISB<3>
Note 1: 8-bit timer is concatenated with the 2-bit internal
Q clock, or 2 bits of the prescaler to create 10-bit
time-base.
A PWM output (Figure 11-3) 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 11-3:
PWM OUTPUT
Period
Duty Cycle
TMR2 = PR2
TMR2 = Duty Cycle
TMR2 = PR2
11.3.1 PWM PERIOD
The PWM period is specified by writing to the
PR2register. The PWM period can be calculated using
the following formula:
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 CCP1 pin is set (exception: if PWM duty
cycle = 0%, the CCP1 pin will not be set)
• The PWM duty cycle is latched from CCPR1L into
CCPR1H
Note:
The Timer2 postscaler (see Section 8.0) is
not used in the determination of the PWM
frequency. The postscaler could be used to
have an interrupt occur at a different fre-
quency than the PWM output.
DS40300C-page 64
Preliminary
 2003 Microchip Technology Inc.