PIC18LF4331 datasheet(181/392 Pages) MICROCHIP

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 2010 Microchip Technology Inc.

DS39616D-page 181

PIC18F2331/2431/4331/4431

Table 18-1 shows the minimum PWM frequencies that

can be generated with the PWM time base and the

prescaler.

operating

frequency

40 MHz

(FCYC = 10 MHz) and PTPER = 0xFFF is assumed in

the table. The PWM module must be capable of gener-

ating PWM signals at the line frequency (50 Hz or

60 Hz) for certain power control applications.

TABLE 18-1:

MINIMUM PWM FREQUENCY

18.3.5

PWM TIME BASE POSTSCALER

The match output of PTMR can optionally be

postscaled through a 4-bit postscaler (which gives a

1:1 to 1:16 scaling inclusive) to generate an interrupt.

The postscaler counter is cleared when any of the

following occurs:

• Write to the PTMR register

• Write to the PTCON register

• Any device Reset

The PTMR register is not cleared when PTCON is

written.

18.4

PWM Time Base Interrupts

The PWM timer can generate interrupts based on the

modes of operation selected by the PTMOD<1:0> bits

and the postscaler bits (PTOPS<3:0>).

18.4.1

INTERRUPTS IN FREE-RUNNING

MODE

When the PWM time base is in the Free-Running mode

(PTMOD<1:0> = 00), an interrupt event is generated

each time a match with the PTPER register occurs. The

PTMR register is reset to zero in the following clock edge.

Using a postscaler selection other than 1:1 will reduce

the frequency of interrupt events.

FIGURE 18-5:

PWM TIME BASE INTERRUPT TIMING, FREE-RUNNING MODE

Minimum PWM Frequencies vs. Prescaler Value

for FCYC = 10 MIPS (PTPER = 0FFFh)

Prescale

PWM Frequency

Edge-Aligned

PWM Frequency

Center-Aligned

1:1

2441 Hz

1221 Hz

1:4

610 Hz

305 Hz

1:16

153 Hz

76 Hz

1:64

38 Hz

19 Hz

FOSC/4

PTMR_INT_REQ

FFEh

FFFh

000h

001h

002h

PTIF bit

Note 1:

PWM Time Base Period register, PTPER, is loaded with the value, FFFh, for this example.

PTIF bit

PTMR

FFEh

FFFh

001h

002h

A: PRESCALER = 1:1

B: PRESCALER = 1:4

PTMR

PTMR_INT_REQ

000h

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