PIC16F684-ESLASHST datasheet(36/164 Pages) MICROCHIP

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PIC16F684

DS41202C-page 34

Preliminary

 2004 Microchip Technology Inc.

4.2.3

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 consump-

tion. The mode is selected by setting the ULPWUE bit

(PCON<5>). This enables a small current sink which

can be used to discharge a capacitor on RA0.

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

‘1’ to charge the capacitor, 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, an interrupt will be generated which will cause

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

GIE bit (INTCON<7>), the device will either jump to the

interrupt vector (0004h) or execute the next instruction

when the interrupt event occurs. See Section 4.2.2

“Interrupt-on-change” and Section 12.4.3 “PORTA

Interrupt” 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 pro-

vide 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).

BCF

STATUS,RP0

;Bank 0

BSF

PORTA,0

;Set RA0 data latch

MOVLW

H’7’

;Turn off

MOVWF

CMCON0

;comparators

BSF

STATUS,RP0

;Bank 1

BCF

ANSEL,0

;RA0 to digital I/O

BCF

TRISA,0

;Output high to

CALL

CapDelay

; charge capacitor

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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