PIC12F683_07 datasheet(37/176 Pages) MICROCHIP

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DS41211D-page 35

PIC12F683

4.2.4

ULTRA LOW-POWER WAKE-UP

The Ultra Low-Power Wake-up (ULPWU) on GP0

allows a slow falling voltage to generate an inter-

rupt-on-change on GP0 without excess current con-

sumption. The mode is selected by setting the

ULPWUE bit of the PCON register. This enables a

small current sink which can be used to discharge a

capacitor on GP0.

To use this feature, the GP0 pin is configured to output

‘1’ to charge the capacitor, interrupt-on-change for GP0

is enabled and GP0 is configured as an input. The ULP-

WUE bit is set to begin the discharge and a SLEEP

instruction is performed. When the voltage on GP0

drops below VIL, an interrupt will be generated which will

cause the device to wake-up. Depending on the state of

the GIE bit of the INTCON register, the device will either

jump to the interrupt vector (0004h) or execute the next

instruction when the interrupt event occurs. See

Section 4.2.3

“Interrupt-on-Change”

and

Section 12.4.3 “GPIO Interrupt” for more information.

This feature provides a low-power technique for period-

ically waking up the device from Sleep. The time-out is

dependent on the discharge time of the RC circuit

on GP0. See Example 4-2 for initializing the Ultra

Low-Power Wake-up module.

The series resistor provides overcurrent protection for

the GP0 pin and can allow for software calibration of the

time-out (see Figure 4-1). A timer can be used to mea-

sure the charge time and discharge time of the capaci-

tor. 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 4-2:

ULTRA LOW-POWER

WAKE-UP INITIALIZATION

Note:

For more information, refer to the Applica-

tion Note AN879, “Using the Microchip

Ultra

Low-Power

Wake-up

Module”

(DS00879).

BANKSEL

CMCON0

;

MOVLW

H’7’

;Turn off

MOVWF

CMCON0

;comparators

BANKSEL

ANSEL

;

BCF

ANSEL,0

;RA0 to digital I/O

BCF

TRISA,0

;Output high to

BANKSEL

PORTA

;

BSF

PORTA,0

;charge capacitor

CALL

CapDelay

;

BANKSEL

PCON

;

BSF

PCON,ULPWUE

;Enable ULP Wake-up

BSF

IOCA,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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