
PIC16F882/883/884/886/887
DS41291D-page 222
Preliminary
 2007 Microchip Technology Inc.
14.6
Power-Down Mode (Sleep)
The Power-down mode is entered by executing a
SLEEP
 instruction. 
If the Watchdog Timer is enabled:
 WDT will be cleared but keeps running.
 PD bit in the STATUS register is cleared.
 TO bit is set.
 Oscillator driver is turned off.
 I/O ports maintain the status they had before 
SLEEP
 was executed (driving high, low or high-
impedance).
For lowest current consumption in this mode, all I/O pins
should be either at V
DD
 or V
SS
, with no external circuitry
drawing current from the I/O pin and the comparators
and CV
REF
 should be disabled. I/O pins that are high-
impedance inputs should be pulled high or low externally
to avoid switching currents caused by floating inputs.
The T0CKI input should also be at V
DD
 or V
SS
 for lowest
current consumption. The contribution from on-chip pull-
ups on PORTA should be considered.
The MCLR pin must be at a logic high level.      
14.6.1
The device can wake-up from Sleep through one of the
following events:
1.
External Reset input on MCLR pin.
2.
Watchdog Timer Wake-up (if WDT was enabled).
3.
Interrupt from RB0/INT pin, PORTB change or a
peripheral interrupt.
The first event will cause a device Reset. The two latter
events are considered a continuation of program exe-
cution. The TO and PD bits in the STATUS register can
be used to determine the cause of device Reset. The
PD bit, which is set on power-up, is cleared when Sleep
is invoked. TO bit is cleared if WDT Wake-up occurred.
The following peripheral interrupts can wake the device
from Sleep:
1.
TMR1 interrupt. Timer1 must be operating as an
asynchronous counter.
2.
ECCP Capture mode interrupt.
3.
A/D conversion (when A/D clock source is FRC).
4.
EEPROM write operation completion.
5.
Comparator output changes state.
6.
Interrupt-on-change.
7.
External Interrupt from INT pin.
8.
EUSART Break detect, I
2
C slave.
Other peripherals cannot generate interrupts since
during Sleep, no on-chip clocks are present.
WAKE-UP FROM SLEEP
When the 
SLEEP
 instruction is being executed, the next
instruction (PC + 1) is prefetched. For the device to
wake-up through an interrupt event, the corresponding
interrupt enable bit must be set (enabled). Wake-up
occurs regardless of the state of the GIE bit. If the GIE
bit is clear (disabled), the device continues execution at
the instruction after the 
SLEEP
 instruction. If the GIE bit
is set (enabled), the device executes the instruction
after the 
SLEEP
 instruction, then branches to the inter-
rupt address (0004h). In cases where the execution of
the instruction following 
SLEEP 
is not desirable, the
user should have a 
NOP
 after the 
SLEEP
 instruction.
The WDT is cleared when the device wakes up from
Sleep, regardless of the source of wake-up.
14.6.2
When global interrupts are disabled (GIE cleared) and
any interrupt source has both its interrupt enable bit
and interrupt flag bit set, one of the following will occur:
 If the interrupt occurs 
before
 the execution of a 
SLEEP
 instruction, the 
SLEEP
 instruction will 
complete as a 
NOP
. Therefore, the WDT and WDT 
prescaler and postscaler (if enabled) will not be 
cleared, the TO bit will not be set and the PD bit 
will not be cleared.
 If the interrupt occurs 
during or after
 the execu-
tion of a 
SLEEP
 instruction, the device will imme-
diately wake-up from Sleep. The 
SLEEP
instruction will be completely executed before the 
wake-up. Therefore, the WDT and WDT prescaler 
and postscaler (if enabled) will be cleared, the TO 
bit will be set and the PD bit will be cleared.
Even if the flag bits were checked before executing a
SLEEP
 instruction, it may be possible for flag bits to
become set before the 
SLEEP
 instruction completes. To
determine whether a 
SLEEP
 instruction executed, test
the PD bit. If the PD bit is set, the 
SLEEP
 instruction
was executed as a 
NOP
.
To ensure that the WDT is cleared, a 
CLRWDT
 instruction
should be executed before a 
SLEEP
 instruction.
WAKE-UP USING INTERRUPTS
Note:
It should be noted that a Reset generated
by a WDT time-out does not drive MCLR
pin low.
Note:
If the global interrupts are disabled (GIE is
cleared), but any interrupt source has both
its interrupt enable bit and the corresponding
interrupt flag bits set, the device will
immediately wake-up from Sleep. The
SLEEP
 instruction is completely executed.