MEC1404 Datasheet, PDF (382/572 Pages) Microchip Technology – Keyboard and Embedded Controller Products for Notebook PC

MEC140X/1X
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.
DS00001956D-page 382
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