PIC16F684 datasheet(36/192 Pages) MICROCHIP

36 / 192 page

PIC16F684

DS41202F-page 34

4.2.4

ULTRA LOW-POWER WAKE-UP

The Ultra Low-Power Wake-Up (ULPWU) on RA0

allows

slow

falling

voltage

generate

interrupt-on-change on RA0 without excess current

consumption. 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 RA0.

To use this feature, the RA0 pin is first configured to output

‘1’ to charge the capacitor. Then interrupt-on-change for

RA0 is enabled, and RA0 is configured as an input. The

ULPWUE bit is set to begin the discharge and a SLEEP

instruction is performed. When the voltage on RA0 drops

below VIL, the device will wake-up and execute the next

instruction. If the GIE bit of the INTCON register is set, the

device will call the interrupt service routine (0004h). See

Section 4.2.3

“Interrupt-on-Change”

and

Section 12.4.3

“PORTA

Interrupt-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 4-2 for initializing the Ultra

Low-Power Wake-Up module.

The series resistor provides overcurrent protection for

the RA0 pin and can allow for software calibration of

the time-out (see Figure 4-1). 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 4-2:

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 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

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