PIC18F87K22 Datasheet, PDF(254/548 Page) Microchip Technology – 64/80-Pin, High-Performance, 1-Mbit Enhanced Flash Microcontrollers with 12-Bit A/D and nanoWatt XLP Technology

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PIC18F87K22 Datasheet, PDF (254/548 Pages) Microchip Technology – 64/80-Pin, High-Performance, 1-Mbit Enhanced Flash Microcontrollers with 12-Bit A/D and nanoWatt XLP Technology

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PIC18F87K22 FAMILY

19.4.2 PWM DUTY CYCLE

The PWM duty cycle is specified, to use CCP4 as an

example, by writing to the CCPR4L register and to the

CCP4CON<5:4> bits. Up to 10-bit resolution is avail-

able. The CCPR4L contains the eight MSbs and the

CCP4CON<5:4> contains the two LSbs. This 10-bit

value is represented by CCPR4L:CCP4CON<5:4>.

The following equation is used to calculate the PWM

duty cycle in time:

EQUATION 19-2:

PWM Duty Cycle = (CCPR4L:CCP4CON<5:4>) â¢

TOSC â¢ (TMR2 Prescale Value)

CCPR4L and CCP4CON<5:4> can be written to at any

time, but the duty cycle value is not latched into

CCPR4H until after a match between PR2 and TMR2

occurs (that is, the period is complete). In PWM mode,

CCPR4H is a read-only register.

The CCPR4H register and a two-bit internal latch are

used to double-buffer the PWM duty cycle. This

double-buffering is essential for glitchless PWM

operation.

When the CCPR4H and two-bit latch match TMR2,

concatenated with an internal two-bit Q clock or two

bits of the TMR2 prescaler, the CCP4 pin is cleared.

The maximum PWM resolution (bits) for a given PWM

frequency is given by the equation:

EQUATION 19-3:

PWM Resolution (max) = l--o---g--l--ï¨ï¦o---F-g--F----P-ï¨-O----2W----S---ï©---CM--------ï¸ï¶-bits

Note:

If the PWM duty cycle value is longer than

the PWM period, the CCP4 pin will not be

cleared.

TABLE 19-6: EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 40 MHz

PWM Frequency

2.44 kHz 9.77 kHz 39.06 kHz 156.25 kHz 312.50 kHz

Timer Prescaler (1, 4, 16)

16

4

1

1

1

PR2 Value

FFh

FFh

FFh

3Fh

1Fh

Maximum Resolution (bits)

10

10

10

8

7

416.67 kHz

1

17h

6.58

19.4.3 SETUP FOR PWM OPERATION

To configure the CCP module for PWM operation,

using CCP4 as an example:

1. Set the PWM period by writing to the PR2

register.

2. Set the PWM duty cycle by writing to the

CCPR4L register and CCP4CON<5:4> bits.

3. Make the CCP4 pin an output by clearing the

appropriate TRIS bit.

4. Set the TMR2 prescale value, then enable

Timer2 by writing to T2CON.

5. Configure the CCP4 module for PWM operation.

TABLE 19-7: REGISTERS ASSOCIATED WITH PWM AND TIMERS

Name

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

INTCON

GIE/GIEH PEIE/GIEL TMR0IE INT0IE

RBIE

TMR0IF INT0IF

RBIF

RCON

PIR4

PIE4

IPR4

IPEN

CCP10IF(1)

CCP10IE(1)

CCP10IP(1)

SBOREN

CCP9IF(1)

CCP9IE(1)

CCP9IP(1)

CM

CCP8IF

CCP8IE

CCP8IP

RI

CCP7IF

CCP7IE

CCP7IP

TO

CCP6IF

CCP6IE

CCP6IP

PD

CCP5IF

CCP5IE

CCP5IP

POR

CCP4IF

CCP4IE

CCP4IP

BOR

CCP3IF

CCP3IE

CCP3IP

TRISB

TRISB7 TRISB6 TRISB5 TRISB4 TRISB3 TRISB2 TRISB1 TRISB0

TRISC

TRISC7 TRISC6 TRISC5 TRISC4 TRISC3 TRISC2 TRISC1 TRISC0

TRISE

TRISE7 TRISE6 TRISE5 TRISE4 TRISE3 TRISE2 TRISE1 TRISE0

Legend: â = unimplemented, read as â0â. Shaded cells are not used by PWM or Timer2/4/6/8.

Note 1: Unimplemented on devices with a program memory of 32 Kbytes (PIC18F65K22 and PIC18F85K22).

2: Unimplemented on 64-pin devices (PIC18F65K22, PIC18F66K22 and PIC18F67K22).

DS39960B-page 254

Preliminary

ï£ 2010 Microchip Technology Inc.

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