PIC18FXX8 Datasheet, PDF (131/402 Pages) Microchip Technology – 28/40-Pin High-Performance, Enhanced Flash Microcontrollers with CAN Module

The maximum PWM resolution (bits) for a given PWM
frequency is given by the following equation.
EQUATION 15-3:
PWM Resolution (max)
=
log


F--F--P^-O--W^{--S---CM---}
----------------------------- bits
log (2)
Note:
If the PWM duty cycle value is longer than
the PWM period, the CCP1 pin will not be
cleared.
PIC18FXX8
15.4.3 SETUP 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 15-4: EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 40 MHz
PWM Frequency
2.44 kHz 9.76 kHz 39.06 kHz 156.3 kHz 312.5 kHz
Timer Prescaler (1, 4, 16)
PR2 Value
Maximum Resolution (bits)
16
4
1
1
1
0FFh
0FFh
0FFh
3Fh
1Fh
10
10
10
8
7
416.6 kHz
1
17h
5.5
TABLE 15-5: REGISTERS ASSOCIATED WITH PWM AND TIMER2
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
INTCON
PIR1
PIE1
IPR1
GIE/
GIEH
PSPIF⁽¹⁾
PSPIE⁽¹⁾
PSPIP⁽¹⁾
PEIE/
GIEL
ADIF
ADIE
ADIP
TMR0IE
RCIF
RCIE
RCIP
INT0IE
TXIF
TXIE
TXIP
RBIE TMR0IF INT0IF RBIF 0000 000x 0000 000u
SSPIF
SSPIE
SSPIP
CCP1IF
CCP1IE
CCP1IP
TMR2IF
TMR2IE
TMR2IP
TMR1IF
TMR1IE
TMR1IP
0000 0000 0000 0000
0000 0000 0000 0000
1111 1111 1111 1111
TRISD
PORTD Data Direction Register
1111 1111 1111 1111
TMR2
Timer2 Module Register
0000 0000 0000 0000
PR2
Timer2 Module Period Register
1111 1111 1111 1111
T2CON
— TOUTPS3 TOUTPS2 TOUTPS1 TOUTPS0 TMR2ON T2CKPS1 T2CKPS0 -000 0000 -000 0000
CCPR1L Capture/Compare/PWM Register1 (LSB)
xxxx xxxx uuuu uuuu
CCPR1H Capture/Compare/PWM Register1 (MSB)
xxxx xxxx uuuu uuuu
CCP1CON
—
—
DC1B1 DC1B0 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.
Note 1: These registers or register bits are not implemented on the PIC18F248 and PIC18F258 and read as ‘0’s.
 2004 Microchip Technology Inc.
DS41159D-page 129