PIC18F6X2X datasheet(165/386 Pages) MICROCHIP

165 / 386 page

 2003 Microchip Technology Inc.

Advance Information

DS39612A-page 163

PIC18F6X2X/8X2X

FIGURE 17-1:

SIMPLIFIED BLOCK DIAGRAM OF THE ENHANCED PWM MODULE

17.4.2

PWM DUTY CYCLE

The PWM duty cycle is specified by writing to the

CCPR1L register and to the CCP1CON<5:4> bits. Up

to 10-bit resolution is available. The CCPR1L contains

the eight MSbs and the CCP1CON<5:4> contains the

two LSbs. This 10-bit value is represented by

CCPRxL:CCPxCON<5:4>. The PWM duty cycle is

calculated by the equation:

CCPR1L and CCP1CON<5:4> can be written to at any

time but the duty cycle value is not copied into

CCPR1H until a match between PR2 and TMR2 occurs

(i.e., the period is complete). In PWM mode, CCPR1H

is a read only register.

The CCPRxH register and a 2-bit internal latch are

used to double-buffer the PWM duty cycle. This

double-buffering is essential for glitchless PWM opera-

tion. 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 equation:

TABLE 17-4:

EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 40 MHz

CCPR1L

CCPR1H (Slave)

Comparator

TMR2

Comparator

PR2

(Note 1)

Duty Cycle Registers

CCP1CON<5:4>

Clear Timer,

set CCP1 pin and

latch D.C.

Note: The 8-bit timer TMR2 register is concatenated with the 2-bit internal Q clock, or 2 bits of the prescaler, to create the 10-bit

time base.

TRISx<x>

CCP1/P1A

TRISx<x>

P1B

TRISx<x>

P1D

Output

Controller

P1M1<1:0>

CCP1M<3:0>

ECCP1DEL

CCP1/P1A

P1B

P1C

P1D

P1C

PWM Duty Cycle =

(CCPR1L:CCP1CON<5:4>) •

TOSC • (TMR2 Prescale Value)

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)

41111

PR2 Value

FFh

3Fh

1Fh

17h

Maximum Resolution (bits)

6.58

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