PIC16F688-ISLASHML datasheet(38/204 Pages) MICROCHIP

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PIC16F688

DS41203E-page 36

4.2.4

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

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 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 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 11.3.3 “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

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 Application

Note AN879, “Using the Microchip Ultra

Low-Power

Wake-up

Module”

(DS00879).

BANKSEL

PORTA

;

BSF

PORTA,0

;Set RA0 data latch

MOVLW

H’7’

;Turn off

MOVWF

CMCON0

; comparators

BANKSEL

ANSEL

;

BCF

ANSEL,0

;RA0 to digital I/O

BANKSEL

TRISA

;

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

NOP

;

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