Datasheet

© 2007 Microchip Technology Inc. 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 V
IL, 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 ;