PIC16C62X
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. PD
bit, which is set on power-up is cleared when SLEEP is
invoked. TO bit is cleared if WDT Wake-up occurred.
9.8
Power-Down Mode (SLEEP)
The Power-down mode is entered by executing a
SLEEPinstruction.
If enabled, the Watchdog Timer will be cleared but
keeps running, the PD bit in the STATUS register is
cleared, the TO bit is set, and the oscillator driver is
turned off. The I/O ports maintain the status they had,
before SLEEP was executed (driving high, low, or
hi-impedance).
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 correspond-
ing 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 SLEEPinstruction. If the GIE bit is
set (enabled), the device executes the instruction after
the SLEEPinstruction 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 an NOPafter the SLEEPinstruction.
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 com-
parators and VREF should be disabled. I/O pins that are
hi-impedance inputs should be pulled high or low exter-
nally 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 PORTB should be considered.
Note: If the global interrupts are disabled (GIE is
cleared), but any interrupt source has both
its interrupt enable bit and the correspond-
ing interrupt flag bits set, the device will
immediately wakeup from sleep.The sleep
instruction is completely executed.
The MCLR pin must be at a logic high level (VIHMC).
Note: It should be noted that a RESET generated
by a WDT time-out does not drive MCLR
pin low.
9.8.1
WAKE-UP FROM SLEEP
The WDT is cleared when the device wakes-up from
sleep, regardless of the source of wake-up.
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, RB Port change, or
the Peripheral Interrupt (Comparator).
FIGURE 9-18: WAKE-UP FROM SLEEP THROUGH INTERRUPT
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
OSC1
CLKOUT(4)
INT pin
TOST(2)
INTF flag
(INTCON<1>)
Interrupt Latency
(Note 2)
GIE bit
(INTCON<7>)
Processor in
SLEEP
INSTRUCTION FLOW
PC
PC
PC+1
PC+2
PC+2
PC + 2
0004h
0005h
Instruction
Inst(0004h)
Inst(PC + 1)
Inst(PC + 2)
Inst(0005h)
Inst(PC) = SLEEP
Inst(PC - 1)
fetched
Instruction
executed
Dummy cycle
Dummy cycle
SLEEP
Inst(PC + 1)
Inst(0004h)
Note 1: XT, HS or LP oscillator mode assumed.
2: TOST = 1024TOSC (drawing not to scale) This delay will not be there for RC osc mode.
3: GIE = '1' assumed. In this case after wake- up, the processor jumps to the interrupt routine. If GIE = '0', execution will continue in-line.
4: CLKOUT is not available in these osc modes, but shown here for timing reference.
1998 Microchip Technology Inc.
Preliminary
DS30235G-page 59
MICROCHIP [ MICROCHIP ]
