PIC16C76-10/JW Microchip Technology, PIC16C76-10/JW Datasheet - Page 74

• Manufacturer Part Number: PIC16C76-10/JW
• Description: 8-Bit CMOS Microcontrollers with A/D Converter
• Manufacturer: Microchip Technology

PIC16C7X
10.3
In Pulse Width Modulation (PWM) mode, the CCPx pin
produces up to a 10-bit resolution PWM output. Since
the CCP1 pin is multiplexed with the PORTC data latch,
the TRISC<2> bit must be cleared to make the CCP1
pin an output.
Figure 10-4 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 10.3.3.
FIGURE 10-4: SIMPLIFIED PWM BLOCK
A PWM output (Figure 10-5) 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 10-5: PWM OUTPUT
DS30390E-page 74
Note 1: 8-bit timer is concatenated with 2-bit internal Q clock
Note:
CCPR1L
CCPR1H (Slave)
Comparator
Duty cycle registers
TMR2 = PR2
PR2
or 2 bits of the prescaler to create 10-bit time-base.
TMR2
Comparator
PWM Mode
Applicable Devices
72 73 73A 74 74A 76 77
Duty Cycle
Clearing the CCP1CON register will force
the CCP1 PWM output latch to the default
low level. This is not the PORTC I/O data
latch.
Period
(Note 1)
DIAGRAM
TMR2 = Duty Cycle
Clear Timer,
CCP1 pin and
latch D.C.
TMR2 = PR2
CCP1CON<5:4>
R
S
Q
TRISC<2>
RC2/CCP1
10.3.1
The PWM period is specified by writing to the PR2 reg-
ister. The PWM period can be calculated using the fol-
lowing formula:
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
• The PWM duty cycle is latched from CCPR1L into
10.3.2
The PWM duty cycle is specified by writing to the
CCPR1L register and to the CCP1CON<5:4> bits. Up
to 10-bit resolution is available: the CCPR1L contains
the eight MSbs and the CCP1CON<5:4> contains the
two LSbs. This 10-bit value is represented by
CCPR1L:CCP1CON<5:4>. The following equation is
used to calculate the PWM duty cycle in time:
CCPR1L and CCP1CON<5:4> can be written to at any
time, but the duty cycle value is not latched into
CCPR1H until after a match between PR2 and TMR2
occurs (i.e., the period is complete). In PWM mode,
CCPR1H is a read-only register.
The CCPR1H 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 CCPR1H and 2-bit latch match TMR2 con-
catenated with an internal 2-bit Q clock or 2 bits of the
TMR2 prescaler, the CCP1 pin is cleared.
Maximum PWM resolution (bits) for a given PWM
frequency:
cycle = 0%, the CCP1 pin will not be set)
CCPR1H
Note:
Note:
PWM duty cycle = (CCPR1L:CCP1CON<5:4>) •
PWM period = [(PR2) + 1] • 4 • T
PWM PERIOD
PWM DUTY CYCLE
The Timer2 postscaler (see Section 9.1) is
not used in the determination of the PWM
frequency. The postscaler could be used to
have a servo update rate at a different fre-
quency than the PWM output.
If the PWM duty cycle value is longer than
the PWM period the CCP1 pin will not be
cleared.
=
(TMR2 prescale value)
log
log(2)
Tosc • (TMR2 prescale value)
(
F
F
1997 Microchip Technology Inc.
PWM
OSC
)
OSC
bits
•