PIC24F32KA302 datasheet(131/364 Pages) MICROCHIP

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DS39995D-page 131

PIC24FV32KA304 FAMILY

10.3

Ultra Low-Power Wake-up

The Ultra Low-Power Wake-up (ULPWU) on pin, RB0,

allows a slow falling voltage to generate an interrupt

without excess current consumption.

To use this feature:

Charge the capacitor on RB0 by configuring the

RB0 pin to an output and setting it to ‘1’.

Stop charging the capacitor by configuring RB0

as an input.

Discharge the capacitor by setting the ULPEN

and ULPSINK bits in the ULPWCON register.

Configure Sleep mode.

Enter Sleep mode.

When the voltage on RB0 drops below VIL, the device

wakes up and executes the next instruction.

This feature provides a low-power technique for

periodically waking up the device from Sleep mode.

The time-out is dependent on the discharge time of the

RC circuit on RB0.

When the ULPWU module wakes the device from

Sleep mode, the ULPWUIF bit (IFS5<0>) is set. Soft-

ware can check this bit upon wake-up to determine the

wake-up source. See Example 10-3 for initializing the

ULPWU module.

A series resistor, between RB0 and the external

capacitor, provides overcurrent protection for the

RB0/AN0/ULPWU pin and enables software calibration

of the time-out (see Figure 10-1).

FIGURE 10-1:

SERIES RESISTOR

A timer can be used to measure the charge time and

discharge time of the capacitor. The charge time can

then be adjusted to provide the desired delay in Sleep.

This technique compensates for the affects of temper-

ature, voltage and component accuracy. The peripheral

can also be configured as a simple, programmable

Low-Voltage Detect (LVD) or temperature sensor.

EXAMPLE 10-3:

ULTRA LOW-POWER

WAKE-UP INITIALIZATION

RB0

//*******************************

// 1. Charge the capacitor on RB0

//*******************************

TRISBbits.TRISB0 = 0;

LATBbits.LATB0 = 1;

for(i = 0; i < 10000; i++) Nop();

//*****************************

//2. Stop Charging the capacitor

on RB0

//*****************************

TRISBbits.TRISB0 = 1;

//*****************************

//3. Enable ULPWU Interrupt

//*****************************

IFS5bits.ULPWUIF = 0;

IEC5bits.ULPWUIE = 1;

IPC21bits.ULPWUIP = 0x7;

//*****************************

//4. Enable the Ultra Low Power

Wakeup module and allow

capacitor discharge

//*****************************

ULPWCONbits.ULPEN = 1;

ULPWCONbit.ULPSINK = 1;

//*****************************

//5. Enter Sleep Mode

//*****************************

Sleep();

//for sleep, execution will

//resume here

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