Microchip Technology DM164134 Data Sheet
© 2006 Microchip Technology Inc.
DS41159E-page 129
PIC18FXX8
The maximum PWM resolution (bits) for a given PWM
frequency is given by the following equation.
frequency is given by the following equation.
EQUATION 15-3:
15.4.3
SETUP FOR PWM OPERATION
The following steps should be taken when configuring
the CCP module for PWM operation:
the CCP module for PWM operation:
1.
Set the PWM period by writing to the PR2
register.
register.
2.
Set the PWM duty cycle by writing to the
CCPR1L register and CCP1CON<5:4> bits.
CCPR1L register and CCP1CON<5:4> bits.
3.
Make the CCP1 pin an output by clearing the
TRISC<2> bit.
TRISC<2> bit.
4.
Set the TMR2 prescale value and enable Timer2
by writing to T2CON.
by writing to T2CON.
5.
Configure the CCP1 module for PWM operation.
TABLE 15-4:
EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 40 MHz
TABLE 15-5:
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.
the PWM period, the CCP1 pin will not be
cleared.
F
OSC
F
PWM
---------------
⎝
⎠
⎛
⎞
log
2
( )
log
-----------------------------bits
=
PWM Resolution (max)
PWM Frequency
2.44 kHz
9.76 kHz
39.06 kHz
156.3 kHz
312.5 kHz
416.6 kHz
Timer Prescaler (1, 4, 16)
16
4
1
1
1
1
PR2 Value
0FFh
0FFh
0FFh
3Fh
1Fh
17h
Maximum Resolution (bits)
10
10
10
8
7
5.5
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
(1)
ADIF
RCIF
TXIF
SSPIF
CCP1IF
TMR2IF
TMR1IF
0000 0000 0000 0000
PIE1
PSPIE
(1)
ADIE
RCIE
TXIE
SSPIE
CCP1IE
TMR2IE
TMR1IE
0000 0000 0000 0000
IPR1
PSPIP
(1)
ADIP
RCIP
TXIP
SSPIP
CCP1IP
TMR2IP
TMR1IP
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.