PIC18CXX2
18.3.2 WAKE-UP USING INTERRUPTS
Even if the flag bits were checked before executing a
SLEEP instruction, it may be possible for flag bits to
become set before the SLEEPinstruction completes. To
determine whether a SLEEPinstruction executed, test
the PD bit. If the PD bit is set, the SLEEP instruction
was executed as a NOP.
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 an interrupt condition (interrupt flag bit and inter-
rupt enable bits are set) occurs before the execu-
tion of a SLEEPinstruction, the SLEEPinstruction
will complete 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.
To ensure that the WDT is cleared, a CLRWDTinstruc-
tion should be executed before a SLEEPinstruction.
• If the interrupt condition occurs during or after
the execution of a SLEEPinstruction, the device
will immediately 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.
FIGURE 18-3: WAKE-UP FROM SLEEP THROUGH INTERRUPT(1,2)
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
(2)
(4)
TOST
CLKOUT
INT pin
INTF flag
(INTCON<1>)
(3)
Interrupt Latency
GIEH bit
(INTCON<7>)
Processor in
SLEEP
INSTRUCTION FLOW
PC
PC
PC+2
PC+4
PC+4
PC + 4
0008h
000Ah
Instruction
Inst(0008h)
Inst(PC + 2)
Inst(PC + 4)
Inst(000Ah)
Inst(PC) = SLEEP
Inst(PC - 1)
fetched
Instruction
executed
Dummy cycle
Dummy cycle
SLEEP
Inst(PC + 2)
Inst(0008h)
Note 1: XT, HS or LP oscillator mode assumed.
2: GIE = '1' assumed. In this case, after wake- up, the processor jumps to the interrupt routine. If GIE = '0',
execution will continue in-line.
3: TOST = 1024TOSC (drawing not to scale) This delay will not occur for RC and EC osc modes.
4: CLKOUT is not available in these osc modes, but shown here for timing reference.
DS39026B-page 188
Preliminary
7/99 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
