PIC16LC771T datasheet(56/224 Pages) MICROCHIP

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PIC16C717/770/771

DS41120C-page 56

 1999-2013 Microchip Technology Inc.

8.3

PWM Mode

In Pulse Width Modulation (PWM) mode, the ECCP

module produces up to a 10-bit resolution PWM output.

Figure 8-3 shows the simplified PWM block diagram.

FIGURE 8-3:

SIMPLIFIED PWM BLOCK DIAGRAM

8.3.1

PWM PERIOD

The PWM period is specified by writing to the PR2 reg-

ister. The PWM period can be calculated using the fol-

lowing formula:

PWM PERIOD = [(PR2) + 1] • 4 • TOSC •

(TMR2 PRESCALE VALUE)

PWM frequency is defined as 1 / [PWM period].

When TMR2 is equal to PR2, the following three events

occur on the next increment cycle:

• TMR2 is cleared

• The CCP1 pin is set (exception: if PWM duty

cycle = 0%, the CCP1 pin will not be set)

• The PWM duty cycle is latched from CCPR1L into

CCPR1H

CCPR1L

CCPR1H (Slave)

Comparator

TMR2

Comparator

PR2

(Note 1)

Duty cycle registers

CCP1CON<5:4>

Clear Timer,

CCP1 pin and

latch D.C.

Note: 8-bit timer TMR2 is concatenated with 2-bit internal Q clock or 2 bits of the prescaler to create 10-bit time-base.

TRISB<3>

RB3/CCP1/P1A

TRISB<5>

RB5/SDO/P1B

TRISB<6>

RB6/T1OSO/T1CKI/

TRISB<7>

RB7/T1OSI/P1D

P1C

OUTPUT

CONTROLLER

PWM1M1<1:0>

CCP1M<3:0>

P1DEL

CCP1/P1A

P1B

P1C

P1D

Note:

The Timer2 postscaler (see Section 7.0) is

not used in the determination of the PWM

frequency. The postscaler could be used to

have a servo update rate at a different fre-

quency than the PWM output.

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