PIC17C75X
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 WDT
time-out occurred (and caused wake-up).
17.4
Power-down Mode (SLEEP)
The Power-down mode is entered by executing a
SLEEPinstruction.This clears the Watchdog Timer and
postscaler (if enabled). The PD bit is cleared and the
TO bit is set (in the CPUSTA register). In SLEEP mode,
the oscillator driver is turned off.The I/O ports maintain
their status (driving high, low, or hi-impedance).
When the SLEEPinstruction 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 GLINTD bit. If the GLINTD
bit is set (disabled), the device continues execution at
the instruction after the SLEEP instruction. If the
GLINTD bit is clear (enabled), the device executes the
instruction after the SLEEP instruction and then
branches to the interrupt vector address. In cases
where the execution of the instruction following SLEEP
is not desirable, the user should have a NOP after the
SLEEPinstruction.
The MCLR/VPP pin must be at a logic high level
(VIHMC). A WDT time-out RESET does not drive the
MCLR/VPP pin low.
17.4.1 WAKE-UP FROM SLEEP
The device can wake-up from SLEEP through one of
the following events:
• POR
• External reset input on MCLR/VPP pin
• WDT Reset (if WDT was enabled)
• BOR
• Interrupt from RA0/INT pin, RB port change,
T0CKI interrupt, or some peripheral Interrupts
Note: If the global interrupt is disabled (GLINTD
is set), but any interrupt source has both its
interrupt enable bit and the corresponding
interrupt flag bit set, the device will imme-
diately wake-up from sleep. The TO bit is
set, and the PD bit is cleared.
The following peripheral interrupts can wake the device
from SLEEP:
The WDT is cleared when the device wakes from
SLEEP, regardless of the source of wake-up.
• Capture interrupts
• USART synchronous slave transmit interrupts
• USART synchronous slave receive interrupts
• A/D conversion complete
17.4.1.1 WAKE-UP DELAY
• SPI slave transmit / receive complete
• I C slave receive
When the oscillator type is configured in XT or LF
mode, the Oscillator Start-up Timer (OST) is activated
on wake-up. The OST will keep the device in reset for
1024TOSC. This needs to be taken into account when
considering the interrupt response time when coming
out of SLEEP.
2
Other peripherals cannot generate interrupts since dur-
ing SLEEP, no on-chip Q clocks are present.
Any reset event will cause a device reset. Any interrupt
event is considered a continuation of program execu-
tion. The TO and PD bits in the CPUSTA register can
FIGURE 17-3: WAKE-UP FROM SLEEP THROUGH INTERRUPT
Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
OSC1
Tost(2)
CLKOUT(4)
INT
(RA0/INT pin)
Interrupt Latency (2)
INTF flag
GLINTD bit
Processor
in SLEEP
INSTRUCTION FLOW
0004h
PC
PC+1
PC+2
0005h
PC
Instruction
Inst (PC+2)
Inst (PC+1)
Inst (PC) = SLEEP
Inst (PC-1)
Inst (PC+1)
SLEEP
fetched
Instruction
executed
Dummy Cycle
Note 1: XT or LF oscillator mode assumed.
2: Tost = 1024Tosc (drawing not to scale). This delay will not be there for RC osc mode.
3: When GLINTD = 0 processor jumps to interrupt routine after wake-up. If GLINTD = 1, execution will continue in line.
4: CLKOUT is not available in these osc modes, but shown here for timing reference.
DS30264A-page 180
Preliminary
1997 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
