![](http://datasheet.mmic.net.cn/260000/PIC16C76_datasheet_15942827/PIC16C76_145.png)
1997 Microchip Technology Inc.
DS30390E-page 145
PIC16C7X
14.8
Power-down Mode (SLEEP)
Applicable Devices
72 73 73A 74 74A 76 77
Power-down mode is entered by executing a
SLEEP
instruction.
If enabled, the Watchdog Timer will be cleared but
keeps running, the PD bit (STATUS<3>) is cleared, the
TO (STATUS<4>) bit is set, and the oscillator driver is
turned off. The I/O ports maintain the status they had,
before the
SLEEP
instruction was executed (driving
high, low, or hi-impedance).
For lowest current consumption in this mode, place all
I/O pins at either V
DD
, or V
SS
, ensure no external cir-
cuitry is drawing current from the I/O pin, power-down
the A/D, disable external clocks. Pull all I/O pins, that
are hi-impedance inputs, 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 PORTB should be considered.
The MCLR pin must be at a logic high level (V
IHMC
).
14.8.1
WAKE-UP FROM SLEEP
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 INT pin, RB port change, or some
Peripheral Interrupts.
External MCLR Reset will cause a device reset. All
other events are considered a continuation of program
execution and cause a "wake-up". 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. The TO
bit is cleared if a WDT time-out occurred (and caused
wake-up).
The following peripheral interrupts can wake the device
from SLEEP:
1.
TMR1 interrupt. Timer1 must be operating as
an asynchronous counter.
2.
SSP (Start/Stop) bit detect interrupt.
3.
SSP transmit or receive in slave mode (SPI/I
2
C).
4.
CCP capture mode interrupt.
5.
Parallel Slave Port read or write.
6.
A/D conversion (when A/D clock source is RC).
7.
Special event trigger (Timer1 in asynchronous
mode using an external clock).
8.
USART TX or RX (synchronous slave mode).
Other peripherals cannot generate interrupts since dur-
ing SLEEP, no on-chip Q clocks are present.
When the
SLEEP
instruction is being executed, the next
instruction (PC + 1) is pre-fetched. For the device to
wake-up through an interrupt event, the corresponding
interrupt enable bit must be set (enabled). Wake-up is
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 and 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.
14.8.2
WAKE-UP USING INTERRUPTS
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 com-
plete as a NOP. Therefore, the WDT and WDT
postscaler will not be cleared, the TO bit will not
be set and PD bits 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 postscaler 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
instruc-
tion should be executed before a
SLEEP
instruction.