MCP39F511N datasheet(41/61 Pages) MICROCHIP

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DS20005473B-page 41

MCP39F511N

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 MCP39F511N,

FTIMER described in this section, with a base frequency

of 32 MHz.

The base period is defined as PTIMER and is

1/[32 MHz]. This 32 MHz time base is fixed due to the

8 MHz internal oscillator or 8 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 (see Figure 8-1) 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).

FIGURE 8-1:

PWM Output.

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 two least significant bits. These two values

together create the PWM Period (see Figure 8-2).

FIGURE 8-2:

PWM Period and

Duty-Cycle Registers.

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 in

Figure 8-2 with 255 for PWM Frequency (8-bit value)

and 1023 for the Duty cycle (10-bit value), with the

prescaler set to divide by 16 (1:0).

Period

Duty Cycle

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 0

0 0 0 0

PWM duty-cycle Register

255

1023

PWM PERIOD

(8-bit)

PWM DUTY

(10-bit)

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