2003 Microchip Technology Inc.
DS30569B-page 59
PIC16F870/871
8.4.3
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 8-2:
EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 20 MHz
TABLE 8-3:
REGISTERS ASSOCIATED WITH CAPTURE, COMPARE, AND TIMER1
PWM Frequency
1.22 kHz
4.88 kHz
19.53 kHz
78.12kHz
156.3 kHz
208.3 kHz
Timer Prescaler (1, 4, 16)
16
4
1
PR2 Value
0xFFh
0x3Fh
0x1Fh
0x17h
Maximum Resolution (bits)
10
8
7
6.5
Address
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
0Bh,8Bh,
10Bh, 18Bh
INTCON
GIE
PEIE
T0IE
INTE
RBIE
T0IF
INTF
RBIF
0000 000x 0000 000u
0Ch
PIR1
PSPIF(1)
ADIF
RCIF
TXIF
CCP1IF
TMR2IF
TMR1IF 0000 -000 0000 -000
8Ch
PIE1
PSPIE(1) ADIE
RCIE
TXIE
—CCP1IE
TMR2IE
TMR1IE 0000 -000 0000 -000
87h
TRISC
PORTC Data Direction Register
1111 1111 1111 1111
0Eh
TMR1L
Holding Register for the Least Significant Byte of the 16-bit TMR1 Register
xxxx xxxx uuuu uuuu
0Fh
TMR1H
Holding Register for the Most Significant Byte of the 16-bit TMR1 Register
xxxx xxxx uuuu uuuu
10h
T1CON
T1CKPS1 T1CKPS0 T1OSCEN T1SYNC TMR1CS TMR1ON --00 0000 --uu uuuu
15h
CCPR1L
Capture/Compare/PWM Register1 (LSB)
xxxx xxxx uuuu uuuu
16h
CCPR1H
Capture/Compare/PWM Register1 (MSB)
xxxx xxxx uuuu uuuu
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 Capture and Timer1.
Note
1:
The PSP is not implemented on the PIC16F870; always maintain these bits clear.
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