MEC1322 Datasheet, PDF (329/456 Pages) Microchip Technology – Keyboard and Embedded Controller for Notebook PC

MEC1322
28.7 Low Power Mode
The Blinking/Breathing PWM may be put into a low power mode by the chip-level power, clocks, and reset (PCR)
circuitry. The low power mode is only applicable when the Blinking/Breathing PWM is operating in the General Pur-
pose PWM mode. When the low speed clock mode is selected, the blinking/breathing function continues to operate,
even when the 48 MHz clock is stopped. Low power mode behavior is summarized in the following table:
TABLE 28-6: LOW POWER MODE BEHAVIOR
CLOCK_S
OURCE
CONTROL
Mode
X
‘00’b
X
‘01’b
1
‘10’b
PWM ‘OFF’
Breathing
General Purpose PWM
0
‘10’b
X
‘11’b
Blinking
PWM ‘ON’
Low Power
Mode
Yes
Yes
No
Yes
Yes
Description
32.768 KHz clock is
required.
48 MHz clock is required,
even when a sleep com-
mand to the block is
asserted.
32.768 KHz clock is
required.
Note:
In order for the MEC1322 to enter its.heavy and deep sleep states, the SLEEP_ENABLE input for all Blink-
ing/Breathing PWM instances must be asserted, even if the PWMs are configured to use the low speed
clock.
28.8 Description
28.8.1 BREATHING
If an LED blinks rapidly enough, the eye will interpret the light as reduced brightness, rather than a blinking pattern.
Therefore, if the blinking period is short enough, modifying the duty cycle will set the apparent brightness, rather than a
blinking rate. At a blinking rate of 128Hz or greater, almost all people will perceive a continuous light source rather than
an intermittent pattern.
Because making an LED appear to breathe is an aesthetic effect, the breathing mechanism must be adjustable or cus-
tomers may find the breathing effect unattractive. There are several variables that can affect breathing appearance, as
described below.
The following figure illustrates some of the variables in breathing:
FIGURE 28-2:
BREATHING LED EXAMPLE
Full on
Full off
RISING RAMP TIME
FALLING RAMP TIME
Max Duty Cycle
Min Duty Cycle
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DS00001719D-page 329