PIC16F72-E Datasheet, PDF (44/136 Pages) Microchip Technology – 28-Pin, 8-Bit CMOS FLASH Microcontoller with A/D Converter

PIC16F72
Maximum PWM resolution (bits) for a given PWM
frequency is calculated using Equation 8-3.
EQUATION 8-3: PWM MAX RESOLUTION
PWM Maximum Resolution =
log
(
FOSC
FPWM
)
bits
log(2)
Note:
If the PWM duty cycle value is longer than
the PWM period, the CCP1 pin will not be
cleared.
For a sample PWM period and duty cycle calculation,
see the PIC™ Mid-Range MCU Reference Manual
(DS33023).
8.3.3 SET-UP 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
CCPR1L register and CCP1CON<5:4> bits.
3. Make the CCP1 pin an output by clearing the
TRISC<2> bit.
4. Set the TMR2 prescale value and enable Timer2
by writing to T2CON.
5. Configure the CCP1 module for PWM operation.
TABLE 8-3: EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 20 MHz
PWM Frequency
1.22 kHz 4.88 kHz 19.53 kHz 78.12 kHz 156.3 kHz 208.3 kHz
Timer Prescaler (1, 4, 16)
PR2 Value
Maximum Resolution (bits)
16
0xFF
10
4
0xFF
10
1
0xFF
10
1
0x3F
8
1
0x1F
7
1
0x17
5.5
TABLE 8-4: REGISTERS ASSOCIATED WITH PWM AND TIMER2
Address Name Bit 7 Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
Value on
POR, BOR
Value on
all other
RESETS
0Bh,8Bh INTCON GIE PEIE TMR0IE INTE
10Bh,18Bh
RBIE TMR0IF INTF
RBIF 0000 000x 0000 000u
0Ch
PIR1
— ADIF
—
—
SSPIF CCP1IF TMR2IF TMR1IF -0-- 0000 0000 0000
8Ch
PIE1
— ADIE
—
—
SSPIE CCP1IE TMR2IE TMR1IE -0-- 0000 0000 0000
87h
TRISC PORTC Data Direction Register
1111 1111 1111 1111
11h
TMR2
Timer2 Module Register
0000 0000 0000 0000
92h
PR2
Timer2 Module Period Register
1111 1111 1111 1111
12h
T2CON
— TOUTPS3 TOUTPS2 TOUTPS1 TOUTPS0 TMR2ON T2CKPS1 T2CKPS0 -000 0000 -000 0000
15h
CCPR1L Capture/Compare/PWM Register1 (LSB)
xxxx xxxx uuuu uuuu
16h
CCPR1H Capture/Compare/PWM Register1 (MSB)
xxxx xxxx uuuu uuuu
17h
CCP1CON —
—
CCP1X CCP1Y CCP1M3 CCP1M2 CCP1M1 CCP1M0 --00 0000 --00 0000
Legend: x = unknown, u = unchanged, - = unimplemented, read as ‘0’. Shaded cells are not used by PWM and Timer2.
DS39597C-page 42
© 2007 Microchip Technology Inc.