PIC16F636T-I Datasheet, PDF (147/234 Pages) Microchip Technology – 8/14-Pin, Flash-Based 8-Bit CMOS Microcontrollers with nanoWatt Technology

PIC12F635/PIC16F636/639
12.12 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 VDD or VSS, with no external circuitry
drawing current from the I/O pin and the comparators
and CVREF 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 VDD or VSS 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.
Note 1: It should be noted that a Reset generated
by a WDT time-out does not drive MCLR
pin low.
2: The Analog Front-End (AFE) section in
the PIC16F639 device is independent of
the microcontroller’s power-down mode
(Sleep). See Section 11.32.2.3 “Sleep
Command” for AFE’s Sleep mode.
12.12.1 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 RA2/INT pin, PORTA change or a
peripheral interrupt.
The first event will cause a device Reset. The two latter
events are considered a continuation of program
execution. 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. Special event trigger (Timer1 in Asynchronous
mode using an external clock).
3. EEPROM write operation completion.
4. Comparator output changes state.
5. Interrupt-on-change.
6. External Interrupt from INT pin.
© 2007 Microchip Technology Inc.
Other peripherals cannot generate interrupts, since
during Sleep, no on-chip clocks are present.
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 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, then branches to the interrupt
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.
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.
The WDT is cleared when the device wakes up from
Sleep, regardless of the source of wake-up.
Note:
If WUR is enabled (WURE = 0 in
Configuration Word), then the Wake-up
Reset module will force a device Reset.
12.12.2 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
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
execution of a SLEEP instruction, the device will
immediately 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.
DS41232D-page 145