PIC18F1230T-I/ML【PDF 34/318 页】IC PIC MCU FLASH 2KX16 28QFN

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PIC18F1230/1330

2009 Microchip Technology Inc.

DS39758D-page 129

14.5

PWM Period

The PWM period is defined by the PTPER register pair

(PTPERL and PTPERH). The PWM period has 12-bit

resolution by combining 4 LSBs of PTPERH and 8 bits

of PTPERL. PTPER is a double-buffered register used

to set the counting period for the PWM time base.

The PTPER buffer contents are loaded into the PTPER

Free-Running and Single-Shot modes: When the

PTMR register is reset to zero after a match with the

PTPER register.

Continuous Up/Down Count modes: When the

PTMR register is zero. The value held in the PTPER

buffer is automatically loaded into the PTPER

(PTEN = 0). Figure 14-9 and Figure 14-10 indicate

the times when the contents of the PTPER buffer

are loaded into the actual PTPER register.

The PWM period can be calculated from the following

formulas:

EQUATION 14-1:

PWM PERIOD FOR

FREE-RUNNING MODE

EQUATION 14-2:

PWM PERIOD FOR

CONTINUOUS UP/DOWN

COUNT MODE

The PWM frequency is the inverse of period; or

EQUATION 14-3:

PWM FREQUENCY

The maximum resolution (in bits) for a given device

oscillator and PWM frequency can be determined from

the following formula:

EQUATION 14-4:

PWM RESOLUTION

The PWM resolutions and frequencies are shown for a

selection of execution speeds and PTPER values in

Table 14-2. The PWM frequencies in Table 14-2 are

calculated for Edge-Aligned PWM mode. For Center-

Aligned mode, the PWM frequencies will be

approximately one-half the values indicated in this

table.

TABLE 14-2:

EXAMPLE PWM

FREQUENCIES AND

RESOLUTIONS

TPWM =

(PTPER + 1) x PTMRPS

FOSC/4

TPWM =

(2 x PTPER) x PTMRPS

FOSC

PWM Frequency =

PWM Period

PWM Frequency = 1/TPWM

FOSC

MIPS

PTPER

Value

PWM

Resolution

PWM

Frequency

40 MHz

0FFFh

14 bits

2.4 kHz

40 MHz

07FFh

13 bits

4.9 kHz

40 MHz

03FFh

12 bits

9.8 kHz

40 MHz

01FFh

11 bits

19.5 kHz

40 MHz

FFh

10 bits

39.0 kHz

40 MHz

7Fh

9 bits

78.1 kHz

40 MHz

3Fh

8 bits

156.2 kHz

40 MHz

1Fh

7 bits

312.5 kHz

40 MHz

0Fh

6 bits

625 kHz

25 MHz

6.25

0FFFh

14 bits

1.5 kHz

25 MHz

6.25

03FFh

12 bits

6.1 kHz

25 MHz

6.25

FFh

10 bits

24.4 kHz

10 MHz

2.5

0FFFh

14 bits

610 Hz

10 MHz

2.5

03FFh

12 bits

2.4 kHz

10 MHz

2.5

FFh

10 bits

9.8 kHz

5 MHz

1.25

0FFFh

14 bits

305 Hz

5 MHz

1.25

03FFh

12 bits

1.2 kHz

5 MHz

1.25

FFh

10 bits

4.9 kHz

4 MHz

0FFFh

14 bits

244 Hz

4 MHz

03FFh

12 bits

976 Hz

4 MHz

FFh

10 bits

3.9 kHz

Note:

For

center-aligned

operation,

PWM

frequencies will be approximately 1/2 the

value indicated in the table.

Resolution =

log(2)

log

FOSC

FPWM

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