PIC16F688T-I/SL View Datasheet(PDF) - Microchip Technology

Part Name

Description

MFG CO.

PIC16F688T-I/SL

14-Pin Flash-Based, 8-Bit CMOS Microcontrollers with nanoWatt Technology

Microchip Technology 

PIC16F688

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.

Note:

For more information, refer to Application

Note AN879, “Using the Microchip Ultra

Low-Power

Wake-up

Module”

(DS00879).

EXAMPLE 4-2:

ULTRA LOW-POWER

WAKE-UP INITIALIZATION

BANKSEL

BSF

MOVLW

MOVWF

BANKSEL

BCF

BANKSEL

BCF

CALL

BSF

BSF

BSF

MOVLW

MOVWF

SLEEP

NOP

PORTA

;

PORTA,0

;Set RA0 data latch

H’7’

;Turn off

CMCON0

; comparators

ANSEL

;

ANSEL,0

;RA0 to digital I/O

TRISA

;

TRISA,0

;Output high to

CapDelay ; charge capacitor

PCON,ULPWUE ;Enable ULP Wake-up

IOCA,0

;Select RA0 IOC

TRISA,0

;RA0 to input

B’10001000’ ;Enable interrupt

INTCON

; and clear flag

;Wait for IOC

;

DS41203C-page 36

© 2007 Microchip Technology Inc.

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