PIC16F882 datasheet(43/288 Pages) MICROCHIP

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Preliminary

DS41291D-page 41

PIC16F882/883/884/886/887

3.2.2

ULTRA LOW-POWER WAKE-UP

The Ultra Low-Power Wake-up (ULPWU) on RA0 allows

a slow falling voltage to generate an interrupt-on-change

on RA0 without excess current consumption. The mode

is selected by setting the ULPWUE bit of the PCON

used to discharge a capacitor on RA0.

Follow these steps to use this feature:

Charge the capacitor on RA0 by configuring the

RA0 pin to output (= 1).

Configure RA0 as an input.

Enable interrupt-on-change for RA0.

Set the ULPWUE bit of the PCON register to

begin the capacitor discharge.

Execute a SLEEP instruction.

When the voltage on RA0 drops below VIL, an interrupt

will be generated which will cause the device to

wake-up and execute the next instruction. If the GIE bit

of the INTCON register is set, the device will then call

the interrupt vector (0004h). See Section 3.4.3 “Inter-

rupt-on-Change” for more information.

This feature provides a low-power technique for

periodically waking up the device from Sleep. The

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

circuit on RA0. See Example 3-2 for initializing the

Ultra Low-Power Wake-up module.

A series resistor between RA0 and the external

capacitor provides overcurrent protection for the

RA0/AN0/ULPWU/C12IN0- pin and can allow for

software calibration of the time-out (see Figure 3-1). 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 interrupt delay.

This technique will compensate for the affects of

temperature, voltage and component accuracy. The

Ultra Low-Power Wake-up peripheral can also be

configured as a simple Programmable Low Voltage

Detect or temperature sensor.

EXAMPLE 3-2:

ULTRA LOW-POWER

WAKE-UP INITIALIZATION

Note:

For more information, refer to AN879,

“Using the Microchip Ultra Low-Power

Wake-up

Module”

Application

Note

(DS00879).

BANKSEL PORTA

;

BSF

PORTA,0

;Set RA0 data latch

BANKSEL ANSEL

;

BCF

ANSEL,0

;RA0 to digital I/O

BANKSEL TRISA

;

BCF

TRISA,0

;Output high to

CALL

CapDelay

;charge capacitor

BANKSEL PIR2

;

BCF

PIR2,ULPWUIF

;Clear flag

BSF

PCON,ULPWUE

;Enable ULP Wake-up

BSF

IOCB,0

;Select RA0 IOC

BSF

TRISA,0

;RA0 to input

MOVLW

B’10001000’

;Enable interrupt

MOVWF

INTCON

;and clear flag

SLEEP

;Wait for IOC

NOP

;

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