MEC1322 datasheet(327/456 Pages) MICROCHIP

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DS00001719D-page 327

MEC1322

28.0 BLINKING/BREATHING PWM

28.1

Introduction

LEDs are used in computer applications to communicate internal state information to a user through a minimal interface.

Typical applications will cause an LED to blink at different rates to convey different state information. For example, an

LED could be full on, full off, blinking at a rate of once a second, or blinking at a rate of once every four seconds, in order

to communicate four different states.

As an alternative to blinking, an LED can “breathe”, that is, oscillate between a bright state and a dim state in a contin-

uous, or apparently continuous manner. The rate of breathing, or the level of brightness at the extremes of the oscillation

period, can be used to convey state information to the user that may be more informative, or at least more novel, than

traditional blinking.

The blinking/breathing hardware is implemented using a PWM. The PWM can be driven either by the 48 MHz clock or

by a 32.768 KHz clock input. When driven by the 48 MHz clock, the PWM can be used as a standard 8-bit PWM in order

to control a fan. When used to drive blinking or breathing LEDs, the 32.768 KHz clock source is used.

Features:

• Each PWM independently configurable

• Each PWM configurable for LED blinking and breathing output

• Highly configurable breathing rate from 60ms to 1min

• Non-linear brightness curves approximated with 8 piece wise-linear segments

• All LED PWMs can be synchronized

• Each PWM configurable for 8-bit PWM support

• Multiple clock rates

• Configurable Watchdog Timer

28.2

Interface

This block is designed to drive a pin on the pin interface and to be accessed internally via a registered host interface.

FIGURE 28-1:

I/O DIAGRAM OF BLOCK

Blinking/Breathing PWM

Signal Description

Clock Inputs

Interrupts

Resets

Host Interface

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