PIC18F258 Datasheet, PDF (129/384 Pages) Microchip Technology – High Performance, 28/40-Pin Enhanced FLASH Microcontrollers with CAN

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
Timer Prescaler (1, 4, 16)
PR2 Value
Maximum Resolution (bits)
2.44 kHz
16
FFh
10
9.76 kHz
4
FFh
10
39.06 kHz
1
FFh
10
156.3 kHz
1
3Fh
8
312.5 kHz
1
1Fh
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
GIE/
GIEH
PEIE/
GIEL
TMR0IE INT0IE
RBIE TMR0IF INT0IF
RBIF 0000 000x 0000 000u
PIR1
PSPIF
ADIF
RCIF
TXIF
SSPIF CCP1IF TMR2IF TMR1IF 0000 0000 0000 0000
PIE1
PSPIE
ADIE
RCIE
TXIE
SSPIE CCP1IE TMR2IE TMR1IE 0000 0000 0000 0000
IPR1
PSPIP
ADIP
RCIP
TXIP
SSPIP CCP1IP TMR2IP TMR1IP 0000 0000 0000 0000
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.
 2002 Microchip Technology Inc.
Preliminary
DS41159B-page 127