PIC16F883-ESLASHSO. datasheet(132/338 Pages) MICROCHIP

132 / 338 page

PIC16F882/883/884/886/887

DS41291G-page 132

 2006-2012 Microchip Technology Inc.

11.5

PWM Mode

The PWM mode generates a Pulse-Width Modulated

signal on the CCPx pin. The duty cycle, period and

resolution are determined by the following registers:

•PR2

•T2CON

• CCPRxL

• CCPxCON

In Pulse-Width Modulation (PWM) mode, the CCP

module produces up to a 10-bit resolution PWM output

on the CCPx pin. Since the CCPx pin is multiplexed

with the PORT data latch, the TRIS for that pin must be

cleared to enable the CCPx pin output driver.

Figure 11-3 shows a simplified block diagram of PWM

operation.

Figure 11-4 shows a typical waveform of the PWM

signal.

For a step-by-step procedure on how to set up the CCP

module for PWM operation, see Section 11.5.7

“Setup for PWM Operation”.

FIGURE 11-3:

SIMPLIFIED PWM BLOCK

DIAGRAM

The PWM output (Figure 11-4) has a time base

(period) and a time that the output stays high (duty

cycle).

FIGURE 11-4:

CCP PWM OUTPUT

11.5.1

PWM PERIOD

The PWM period is specified by the PR2 register of

Timer2. The PWM period can be calculated using the

formula of Equation 11-1.

EQUATION 11-1:

PWM PERIOD

When TMR2 is equal to PR2, the following three events

occur on the next increment cycle:

•TMR2 is cleared

• The CCPx pin is set. (Exception: If the PWM duty

cycle = 0%, the pin will not be set.)

• The PWM duty cycle is latched from CCPRxL into

CCPRxH.

Note:

Clearing the CCPxCON register will

relinquish CCPx control of the CCPx pin.

CCPRxL

CCPRxH(2) (Slave)

Comparator

TMR2

PR2

(1)

Duty Cycle Registers

CCPxCON<5:4>

Clear Timer2,

toggle CCPx pin and

latch duty cycle

Note 1:

The 8-bit timer TMR2 register is concatenated

with the 2-bit internal system clock (FOSC), or

2 bits of the prescaler, to create the 10-bit time

base.

In PWM mode, CCPRxH is a read-only register.

TRIS

CCPx

Comparator

Note:

The Timer2 postscaler (see Section 7.1

“Timer2 Operation”) is not used in the

determination of the PWM frequency.

Period

Pulse Width

TMR2 = 0

TMR2 = CCPRxL:CCPxCON<5:4>

TMR2 = PR2

PWM Period

PR2

 1

 4TOSC 



(TMR2 Prescale Value)

Note:

TOSC = 1/FOSC

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