PIC16F1526 datasheet(194/354 Pages) MICROCHIP

194 / 354 page

PIC16(L)F1526/27

DS41458A-page 194

Preliminary

 2011 Microchip Technology Inc.

20.3.5

PWM DUTY CYCLE

The PWM duty cycle is specified by writing a 10-bit

value to multiple registers: CCPRxL register and

DCxB<1:0> bits of the CCPxCON register. The

CCPRxL contains the eight MSbs and the DCxB<1:0>

bits of the CCPxCON register contain the two LSbs.

CCPRxL and DCxB<1:0> bits of the CCPxCON

value is not latched into CCPRxH until after the period

completes (i.e., a match between PRx and TMRx

registers occurs). While using the PWM, the CCPRxH

Equation 20-2 is used to calculate the PWM pulse

width.

Equation 20-3 is used to calculate the PWM duty cycle

ratio.

EQUATION 20-2:

PULSE WIDTH

EQUATION 20-3:

DUTY CYCLE RATIO

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 operation.

The 8-bit timer TMRx register is concatenated with either

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

prescaler, to create the 10-bit time base. The system

clock is used if the Timer2/4/6/8/10 prescaler is set to

1:1.

When the 10-bit time base matches the CCPRxH and

2-bit latch, then the CCPx pin is cleared (see

Figure 20-4).

20.3.6

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 PRx is

255. The resolution is a function of the PRx register

value as shown by Equation 20-4.

EQUATION 20-4:

PWM RESOLUTION

TABLE 20-7:

EXAMPLE PWM FREQUENCIES AND RESOLUTIONS (FOSC = 20 MHz)

TABLE 20-8:

EXAMPLE PWM FREQUENCIES AND RESOLUTIONS (FOSC = 8 MHz)

Pulse Width

CCPRxL:CCPxCON<5:4>





TOSC

 (TMRx Prescale Value)

Duty Cycle Ratio

CCPRxL:CCPxCON<5:4>



4 PRx



-----------------------------------------------------------------------

Note:

If the pulse width value is greater than the

period the assigned PWM pin(s) will

remain unchanged.

Resolution

4PRx





log



log

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

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)

PRx Value

0xFF

0x3F

0x1F

0x17

Maximum Resolution (bits)

6.6

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)

PRx Value

0x65

0x19

0x0C

0x09

Maximum Resolution (bits)

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