PIC16C925T-SSLASHCL datasheet(59/182 Pages) MICROCHIP

59 / 182 page

 2001 Microchip Technology Inc.

Preliminary

DS39544A-page 57

PIC16C925/926

EQUATION 8-1:

EXAMPLES OF PWM PERIOD AND DUTY CYCLE CALCULATION

At most, an 8-bit resolution duty cycle can be obtained

from a 31.25 kHz frequency and a 8 MHz oscillator, i.e.,

≤ CCPR1L:CCP1CON<5:4> ≤ 255. Any value greater

than 255 will result in a 100% duty cycle.

In order to achieve higher resolution, the PWM fre-

quency must be decreased. In order to achieve higher

PWM frequency, the resolution must be decreased.

Table 8-2 lists example PWM frequencies and resolu-

tions for FOSC = 8 MHz. TMR2 prescaler and PR2 val-

ues are also shown.

8.3.3

SET-UP FOR PWM OPERATION

The following steps should be taken when configuring

the CCP module for PWM operation:

Set the PWM period by writing to the PR2

Set the PWM duty cycle by writing to the

CCPR1L register and CCP1CON<5:4> bits.

Make the CCP1 pin an output by clearing the

TRISC<2> bit.

Set the TMR2 prescale value and enable Timer2

by writing to T2CON.

Configure the CCP module for PWM operation.

TABLE 8-2:

EXAMPLE PWM FREQUENCIES AND RESOLUTIONS AT 8 MHz

Find the value of the PR2 register, given:

• Desired PWM frequency = 31.25 kHz

• FOSC = 8 MHz

• TMR2 prescale = 1

From the equation for PWM period in Section 8.3.1,

1 / 31.25 kHz

= [ (PR2) + 1 ] • 4 • 1/8 MHz • 1

µs

= [ (PR2) + 1 ] • 4 • 125 ns • 1 = [ (PR2) + 1 ] • 0.5

µs

PR2

= (32

µs / 0.5 µs) - 1

PR2

= 63

Find the maximum resolution of the duty cycle that can be used with a 31.25 kHz frequency and

8 MHz oscillator.

From the equation from maximum PWM resolution in Section 8.3.2,

1 / 31.25 kHz

= 2

PWM RESOLUTION • 1 / 8 MHz • 1

µs= 2PWM RESOLUTION • 125 ns • 1

256

= 2

PWM RESOLUTION

log(256)

= (PWM Resolution) • log(2)

8.0

= PWM Resolution

PWM Frequency

488 Hz

1.95 kHz

7.81 kHz

31.25 kHz

62.5 kHz

250 kHz

Timer Prescaler (1, 4, 16)

PR2 Value

0xFF

0x3F

0x1F

0x07

Maximum Resolution (bits)

PIC16C925T-S/CL 数据表(PDF) 59 Page - Microchip Technology

PIC16C925T-S/CL 数据表(HTML) 59 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表下载