PIC18F6X2X Datasheet, PDF (165/386 Pages) Microchip Technology – 64/80-Pin High Performance, 64-Kbyte Enhanced FLASH Microcontrollers with A/D

PIC18F6X2X/8X2X
FIGURE 17-1:
SIMPLIFIED BLOCK DIAGRAM OF THE ENHANCED PWM MODULE
Duty Cycle Registers
CCPR1L
CCP1CON<5:4>
CCPR1H (Slave)
Comparator
R
TMR2
(Note 1)
S
Comparator
PR2
Clear Timer,
set CCP1 pin and
latch D.C.
P1M1<1:0>
2
CCP1M<3:0>
4
CCP1/P1A
TRISx<x>
P1B
Q
Output
Controller
TRISx<x>
P1C
TRISx<x>
P1D
TRISx<x>
ECCP1DEL
CCP1/P1A
P1B
P1C
P1D
Note: The 8-bit timer TMR2 register is concatenated with the 2-bit internal Q clock, or 2 bits of the prescaler, to create the 10-bit
time base.
17.4.2 PWM DUTY CYCLE
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
CCPRxL:CCPxCON<5:4>. The PWM duty cycle is
calculated by the equation:
PWM Duty Cycle = (CCPR1L:CCP1CON<5:4>) •
TOSC • (TMR2 Prescale Value)
CCPR1L and CCP1CON<5:4> can be written to at any
time but the duty cycle value is not copied into
CCPR1H until a match between PR2 and TMR2 occurs
(i.e., the period is complete). In PWM mode, CCPR1H
is a read only register.
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 opera-
tion. When the CCPR1H and 2-bit latch match TMR2,
concatenated with an internal 2-bit Q clock or two bits
of the TMR2 prescaler, the CCP1 pin is cleared. The
maximum PWM resolution (bits) for a given PWM
frequency is given by the equation:
( ) ^{log FOSC}
PWM Resolution (max) =
FPWM _bits
log(2)
Note:
If the PWM duty cycle value is longer than
the PWM period, the CCP1 pin will not be
cleared.
TABLE 17-4: 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
 2003 Microchip Technology Inc.
Advance Information
DS39612A-page 163