MEC1404 Datasheet, PDF (385/572 Pages) Microchip Technology – Keyboard and Embedded Controller Products for Notebook PC

MEC140X/1X
TABLE 28-2: LOW POWER MODE BEHAVIOR
CLOCK_
SOURCE
X
X
1
CONTROL
‘00’b
‘01’b
‘10’b
Mode
PWM ‘OFF’
Breathing
General Purpose PWM
0
‘10’b
X
‘11’b
Blinking
PWM ‘ON’
Low Power
Mode
Description
Yes
32.768 KHz clock is
required.
Yes
No
48 MHz clock is required,
even when a sleep com-
mand to the block is
asserted.
Yes
32.768 KHz clock is
required.
Yes
Note:
In order for the MEC140X/1X to enter its heavy and deep sleep states, the SLEEP_ENABLE input for all
Blinking/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
Max Duty Cycle
Full off
RISING RAMP TIME
FALLING RAMP TIME
Min Duty Cycle
The breathing range of and LED can range between full on and full off, or in a range that falls within the full-on/full-off
range, as shown in this figure. The ramp time can be different in different applications. For example, if the ramp time
was 1 second, the LED would appear to breathe quickly. A time of 2 seconds would make the LED appear to breathe
more leisurely.
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DS00001956D-page 385