PIC16F688
4.2.4
ULTRA LOW-POWER WAKE-UP
EXAMPLE 4-2:
ULTRA LOW-POWER
WAKE-UP INITIALIZATION
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.
BANKSEL PORTA
;
BSF
PORTA,0
;Set RA0 data latch
;Turn off
; comparators
;
;RA0 to digital I/O
;
;Output high to
; charge capacitor
MOVLW
MOVWF
H’7’
CMCON0
BANKSEL ANSEL
BCF
ANSEL,0
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
BANKSEL TRISA
BCF
CALL
BSF
TRISA,0
CapDelay
PCON,ULPWUE ;Enable ULP Wake-up
BSF
IOCA,0
;Select RA0 IOC
;RA0 to input
B’10001000’ ;Enable interrupt
BSF
TRISA,0
MOVLW
MOVWF
SLEEP
NOP
INTCON
; and clear flag
;Wait for IOC
;
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).
DS41203C-page 36
© 2007 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
