Datasheet

PIC18F2331/2431/4331/4431
DS39616D-page 150  2010 Microchip Technology Inc.
The CCPR1H register and a 2-bit internal latch are
used to double buffer the PWM duty cycle. This double
buffering is essential for glitchless PWM operation.
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 following equation:
EQUATION 16-3:
16.5.3 SETUP FOR PWM OPERATION
The following steps should be taken when configuring
the CCP1 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 16-3: EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 40 MHz
TABLE 16-4: REGISTERS ASSOCIATED WITH PWM AND TIMER2
Note: If the PWM duty cycle value is longer than
the PWM period, the CCP1 pin will not be
cleared.
PWM Resolution (max) =
FOSC
FPWM
log
log(2)
bits




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)1641111
PR2 Value FFh FFh FFh 3Fh 1Fh 17h
Maximum Resolution (bits) 10 10 10 8 7 6.58
Name Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
Reset Values
on Page:
INTCON GIE/GIEH PEIE/GIEL
TMR0IE INT0IE RBIE TMR0IF INT0IF RBIF 54
PIR1
— ADIF RCIF TXIF SSPIF CCP1IF TMR2IF TMR1IF 57
PIE1 — ADIE RCIE TXIE SSPIE CCP1IE TMR2IE TMR1IE 57
IPR1 — ADIP RCIP TXIP SSPIP CCP1IP TMR2IP TMR1IP 57
TRISC PORTC Data Direction Register 57
TMR2 Timer2 Register 55
PR2 Timer2 Period Register 55
T2CON
— TOUTPS3 TOUTPS2 TOUTPS1 TOUTPS0 TMR2ON T2CKPS1 T2CKPS0 55
CCPR1L Capture/Compare/PWM Register 1 Low Byte 56
CCPR1H Capture/Compare/PWM Register 1 High Byte 56
CCP1CON
— — DC1B1 DC1B0 CCP1M3 CCP1M2 CCP1M1 CCP1M0 56
CCPR2L Capture/Compare/PWM Register 2 Low Byte 56
CCPR2H Capture/Compare/PWM Register 2 High Byte 56
CCP2CON
— — DC2B1 DC2B0 CCP2M3 CCP2M2 CCP2M1 CCP2M0 56
Legend: x = unknown, u = unchanged, - = unimplemented, read as ‘0’. Shaded cells are not used by PWM and
Timer2.