PIC18LF4331-ESLASHML datasheet(185/392 Pages) MICROCHIP

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 2010 Microchip Technology Inc.

DS39616D-page 185

PIC18F2331/2431/4331/4431

18.5

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 register contents are loaded into the

PTPER register at the following times:

• 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 register is automatically loaded into the

PTPER register when the PWM time base is

disabled (PTEN = 0). Figure 18-9 and

Figure 18-10 indicate the times when the contents

of the PTPER register are loaded into the actual

PTPER register.

The PWM period can be calculated from the following

formulas:

EQUATION 18-1:

PWM PERIOD FOR

FREE-RUNNING MODE

EQUATION 18-2:

PWM PERIOD FOR

UP/DOWN COUNT MODE

The PWM frequency is the inverse of period; or:

EQUATION 18-3:

PWM FREQUENCY

The maximum resolution (in bits) for a given device

oscillator and PWM frequency can be determined from

the following formula:

EQUATION 18-4:

PWM RESOLUTION

The PWM resolutions and frequencies are shown for a

selection of execution speeds and PTPER values in

Table 18-2. The PWM frequencies in Table 18-2 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 18-2:

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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