PIC16F818/819
The maximum PWM resolution (bits) for a given PWM
frequency is given by the following formula.
9.3.3
SETUP FOR PWM OPERATION
The following steps should be taken when configuring
the CCP module for PWM operation:
EQUATION 9-3:
1. Set the PWM period by writing to the PR2 register.
FOSC
log( )
2. Set the PWM duty cycle by writing to the
CCPR1L register and CCP1CON<5:4> bits.
FPWM
Resolution
bits
=
log(2)
3. Make the CCP1 pin an output by clearing the
TRISB<x> bit.
Note:
If the PWM duty cycle value is longer than
the PWM period, the CCP1 pin will not be
cleared.
4. Set the TMR2 prescale value and enable Timer2
by writing to T2CON.
5. Configure the CCP1 module for PWM operation.
Note:
The TRISB bit (2 or 3) is dependant upon
the setting of configuration bit 12
(CCPMX).
TABLE 9-3:
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
16
0xFF
10
4
1
1
0x3F
8
1
0x1F
7
1
0xFF
10
0xFF
10
0x17
5.5
Maximum Resolution (bits)
TABLE 9-4:
REGISTERS ASSOCIATED WITH PWM AND TIMER2
Value on
all other
Resets
Value on
POR, BOR
Address
Name
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
0Bh,8Bh
INTCON
GIE
PEIE
TMR0IE
INTE
RBIE
TMR0IF
INTF
RBIF
0000 000x 0000 000u
10Bh,18Bh
0Ch
8Ch
86h
PIR1
—
—
ADIF
ADIE
—
—
—
—
SSPIF
SSPIE
CCP1IF TMR2IF TMR1IF -0-- 0000 -0-- 0000
CCP1IE TMR2IE TMR1IE -0-- 0000 -0-- 0000
1111 1111 1111 1111
PIE1
TRISB
TMR2
PR2
PORTB Data Direction Register
Timer2 Module Register
11h
0000 0000 0000 0000
92h
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 Register 1 (LSB)
CCPR1H Capture/Compare/PWM Register 1 (MSB)
xxxx xxxx uuuu uuuu
xxxx xxxx uuuu uuuu
16h
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.
2004 Microchip Technology Inc.
DS39598E-page 69
MICROCHIP [ MICROCHIP ]
