PIC16F688
4.2.3
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
(PCON<5>). This enables a small current sink which
can be used to discharge a capacitor on RA0.
BCF
BSF
MOVLW
MOVWF
BSF
BCF
BCF
CALL
BSF
BSF
STATUS,RP0
;Bank 0
PORTA,0
H’7’
CMCON0
;Set RA0 data latch
;Turn off
; comparators
;Bank 1
;RA0 to digital I/O
;Output high to
; charge capacitor
STATUS,RP0
ANSEL,0
TRISA,0
CapDelay
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 11.5.3
“PORTA Interrupt” for more information.
PCON,ULPWUE
IOCA,0
;Enable ULP Wake-up
;Select RA0 IOC
;RA0 to input
BSF
TRISA,0
MOVLW
MOVWF
SLEEP
B’10001000’
INTCON
;Enable interrupt
; and clear flag
;Wait for IOC
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).
DS41203B-page 34
Preliminary
2004 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
