PIC16F720-ESLASHML datasheet(116/244 Pages) MICROCHIP

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PIC16F/LF720/721

DS41430A-page 116

 2010 Microchip Technology Inc.

15.3.4

PWM RESOLUTION

The resolution determines the number of available duty

cycles for a given period. For example, a 10-bit resolution

will result in 1024 discrete duty cycles, whereas an 8-bit

resolution will result in 256 discrete duty cycles.

The maximum PWM resolution is 10 bits when PR2 is

255. The resolution is a function of the PR2 register

value as shown by Equation 15-4.

EQUATION 15-4:

PWM RESOLUTION

15.3.5

OPERATION IN SLEEP MODE

In Sleep mode, the TMR2 register will not increment

and the state of the module will not change. If the CCP1

pin is driving a value, it will continue to drive that value.

When the device wakes up, TMR2 will continue from its

previous state.

15.3.6

CHANGES IN SYSTEM CLOCK

FREQUENCY

The PWM frequency is derived from the system clock

frequency (FOSC). Any changes in the system clock fre-

quency will result in changes to the PWM frequency.

Refer

Section 7.0

“Oscillator

Module”

for

additional details.

15.3.7

EFFECTS OF RESET

Any Reset will force all ports to Input mode and the

CCP registers to their Reset states.

15.3.8

SETUP FOR PWM OPERATION

The following steps should be taken when configuring

the CCP module for PWM operation:

Disable the PWM pin (CCP1) output driver(s) by

setting the associated TRIS bit(s).

Load the PR2 register with the PWM period value.

Configure the CCP module for the PWM mode

by loading the CCP1CON register with the

appropriate values.

Load the CCPR1L register and the DCxBx bits of

the CCP1CON register, with the PWM duty cycle

value.

Configure and start Timer2:

• Clear the TMR2IF interrupt flag bit of the PIR1

• Configure the T2CKPS bits of the T2CON

• Enable Timer2 by setting the TMR2ON bit of

the T2CON register.

Enable PWM output pin:

• Wait until Timer2 overflows, TMR2IF bit of the

PIR1 register is set. See Note below.

• Enable the PWM pin (CCP1) output driver(s)

by clearing the associated TRIS bit(s).

Note:

If the pulse width value is greater than the

period the assigned PWM pin(s) will

remain unchanged.

Resolution

4PR2





log



log

------------------------------------------ bits

TABLE 15-4:

EXAMPLE PWM FREQUENCIES AND RESOLUTIONS (FOSC = 20 MHz)

PWM Frequency

1.22 kHz

4.88 kHz

19.53 kHz

78.12 kHz

156.3 kHz

208.3 kHz

Timer Prescale (1, 4, 16)

PR2 Value

0xFF

0x3F

0x1F

0x17

Maximum Resolution (bits)

6.6

TABLE 15-5:

EXAMPLE PWM FREQUENCIES AND RESOLUTIONS (FOSC = 8 MHz)

PWM Frequency

1.22 kHz

4.90 kHz

19.61 kHz

76.92 kHz

153.85 kHz

200.0 kHz

Timer Prescale (1, 4, 16)

PR2 Value

0x65

0x19

0x0C

0x09

Maximum Resolution (bits)

Note:

In order to send a complete duty cycle and

period on the first PWM output, the above

steps must be included in the setup

sequence. If it is not critical to start with a

complete PWM signal on the first output,

then step 6 may be ignored.

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