MEC1322 datasheet(331/456 Pages) MICROCHIP

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DS00001719D-page 331

MEC1322

28.8.2

BLINKING

When configured for blinking, a subset of the hardware used in breathing is used to implement the blinking function. The

PWM (an 8-bit accumulator plus an 8-bit duty cycle register) drives the LED directly. The Duty Cycle register is pro-

grammed directly by the user, and not modified further. The PWM accumulator is configured as a simple 8-bit up counter.

The counter uses the 32.768 KHz clock, and is pre-scaled by the Delay counter, to slow the PWM down from the 128Hz

provided by directly running the PWM on the 32.768 KHz clock.

With the pre-scaler, the blink rate of the LED could be as fast as 128Hz (which, because it is blinking faster than the eye

can distinguish, would appear as a continuous level) to 0.03125Hz (that is, with a period of 7.8ms to 32 seconds). Any

duty cycle from 0% (0h) to 100% (FFh) can be configured, with an 8-bit precision. An LED with a duty cycle value of 0h

will be fully off, while an LED with a duty cycle value of FFh will be fully on.

In Blinking mode the PWM counter is always in 8-bit mode.

Table 28-7, "LED Blink Configuration Examples" shows some example blinking configurations:

The Blinking and General Purpose PWM modes share the hardware used in the breathing mode. The Prescale value

is derived from the LD field of the LED_DELAY register and the Duty Cycle is derived from the MIN field of the LED_LIM-

ITS register.

28.8.3

GENERAL PURPOSE PWM

When used in the Blinking configuration with the 48 MHz Ring Oscillator, the LED module can be used as a general-

purpose programmable Pulse-Width Modulator with an 8-bit programmable pulse width. It can be used for fan speed

control, sound volume, etc. With the 48 MHz Ring Oscillator source, the PWM frequency can be configured in the range

shown in Table 28-9.

TABLE 28-7:

LED BLINK CONFIGURATION EXAMPLES

Prescale

Duty Cycle

Blink Frequency

Blink

000h

00h

128Hz

full off

000h

FFh

128Hz

full on

001h

40h

64Hz

3.9ms on, 11.6ms off

003h

80h

32Hz

15.5ms on, 15.5ms off

07Fh

20h

1Hz

125ms on, 0.875s off

0BFh

16h

0.66Hz

125ms on, 1.375s off

0FFh

10h

0.5Hz

125ms on, 1.875s off

180h

0Bh

0.33Hz

125ms on, 2.875s off

1FFh

40h

0.25Hz

1s on, 3s off

TABLE 28-8:

BLINKING MODE CALCULATIONS

Parameter

Unit

Equation

Frequency

(32KHz_Clk frequency) /(PRESCALE + 1)/255

‘H’ Width

Seconds

(1/PERIOD) x (DutyCycle/255)

‘L’ Width

Seconds

(1/PERIOD) x (255 - DutyCycle)

TABLE 28-9:

PWM CONFIGURATION EXAMPLES

Prescale

PWM Frequency

000h

187.5 KHz

001h

93.75 KHz

003h

46.875 KHz

006h

26.8 KHz

00Bh

15.625 KHz

07Fh

1.46 KHz

1FFh

366 Hz

FFFh

46 Hz

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