MEC1322 datasheet(329/456 Pages) MICROCHIP

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DS00001719D-page 329

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:

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

TABLE 28-6:

LOW POWER MODE BEHAVIOR

CLOCK_S

OURCE

CONTROL

Mode

Low Power

Mode

Description

‘00’b

PWM ‘OFF’

Yes

32.768 KHz clock is

required.

‘01’b

Breathing

Yes

‘10’b

General Purpose PWM

48 MHz clock is required,

even when a sleep com-

mand to the block is

asserted.

‘10’b

Blinking

Yes

32.768 KHz clock is

required.

‘11’b

PWM ‘ON’

Yes

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.

Full off

Full on

RISING RAMP TIME

FALLING RAMP TIME

Min Duty Cycle

Max Duty Cycle

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