MCP39F511 datasheet(43/62 Pages) MICROCHIP

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DS20005393B-page 43

MCP39F511

8.0

PULSE WIDTH MODULATION

(PWM)

8.1

Overview

The PWM output pin gives up to a 10-bit resolution of a

pulse width modulated signal. The PWM output is con-

trolled by an internal timer inside the MCP39F511,

FTIMER described in this section, with a base frequency

of 16 MHz. The base period is defined as PTIMER and

is 1/[16 MHz]. This 16 MHz time base is fixed due to the

4 MHz internal oscillator or 4 MHz external crystal.

The output of the PWM is active only when the PWM

Control register has a value of 0x0001. The PWM out-

put is turned off when the register has a value of

0x0000.

The PWM output (Figure 8-2) has a time base (period)

and a time that the output stays high (duty cycle). The

frequency of the PWM is the inverse of the period

(1/period).

There are two registers that control the PWM output,

PWM Period and PWM Duty Cycle.

The 8-bit PWM Period is controlled by a 16-bit register

that contains the period bits and also the prescaler bits.

The PWM Period bits are the most significant eight bits

in the register, and the prescaler value is represented

by the least two significant bits. These two values

together create the PWM Period; see Figure 8-1.

The 10-bit PWM Duty Cycle is controlled by a 16-bit

MSB and the 2 LSB, corresponding to the 2 LSBs of the

10-bit value.

An example of the register’s values are shown here

with 255 for PWM Frequency (8-bit value) and 1023 for

the Duty cycle (10-bit value), prescaler set to divide by

16 (1:0).

FIGURE 8-1:

PWM Period and

Duty-Cycle Registers.

FIGURE 8-2:

PWM Output.

Prescaler

Period

1 1 1 1

0 0 1 0

0 0 0 0

PWM Period Register

LSB

MSB

1 1 1 1

0 0 1 1

0 0 0 0

PWM Duty Cycle Register

255

1023

PWM PERIOD

(8-bit)

PWM DUTY

(10-bit)

Period

Duty Cycle

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