PIC18F25K20T-ISS Datasheet, PDF (48/456 Pages) Microchip Technology – 28/40/44-Pin Flash Microcontrollers with nanoWatt XLP Technology

PIC18F2XK20/4XK20
3.4.3 RC_IDLE MODE
In RC_IDLE mode, the CPU is disabled but the periph-
erals continue to be clocked from the internal oscillator
block from the HFINTOSC multiplexer output. This
mode allows for controllable power conservation during
Idle periods.
From RC_RUN, this mode is entered by setting the
IDLEN bit and executing a SLEEP instruction. If the
device is in another Run mode, first set IDLEN, then set
the SCS1 bit and execute SLEEP. It is recommended
that SCS0 also be cleared, although its value is
ignored, to maintain software compatibility with future
devices. The HFINTOSC multiplexer may be used to
select a higher clock frequency by modifying the IRCF
bits before executing the SLEEP instruction. When the
clock source is switched to the HFINTOSC multiplexer,
the primary oscillator is shut down and the OSTS bit is
cleared.
If the IRCF bits are set to any non-zero value, or the
INTSRC bit is set, the HFINTOSC output is enabled.
The IOFS bit becomes set, after the HFINTOSC output
becomes stable, after an interval of TIOBST
(parameter 39, Table 26-10). Clocks to the peripherals
continue while the HFINTOSC source stabilizes. If the
IRCF bits were previously at a non-zero value, or
INTSRC was set before the SLEEP instruction was exe-
cuted and the HFINTOSC source was already stable,
the IOFS bit will remain set. If the IRCF bits and
INTSRC are all clear, the HFINTOSC output will not be
enabled, the IOFS bit will remain clear and there will be
no indication of the current clock source.
When a wake event occurs, the peripherals continue to
be clocked from the HFINTOSC multiplexer output.
After a delay of TCSD following the wake event, the
CPU begins executing code being clocked by the
HFINTOSC multiplexer. The IDLEN and SCS bits are
not affected by the wake-up. The LFINTOSC source
will continue to run if either the WDT or the Fail-Safe
Clock Monitor is enabled.
3.5 Exiting Idle and Sleep Modes
An exit from Sleep mode or any of the Idle modes is
triggered by any one of the following:
• an interrupt
• a Reset
• a watchdog time-out
This section discusses the triggers that cause exits
from power-managed modes. The clocking subsystem
actions are discussed in each of the power-managed
modes (see Section 3.2 “Run Modes”, Section 3.3
“Sleep Mode” and Section 3.4 “Idle Modes”).
3.5.1 EXIT BY INTERRUPT
Any of the available interrupt sources can cause the
device to exit from an Idle mode or the Sleep mode to
a Run mode. To enable this functionality, an interrupt
source must be enabled by setting its enable bit in one
of the INTCON or PIE registers. The PEIE bIt must also
be set If the desired interrupt enable bit is in a PIE reg-
ister. The exit sequence is initiated when the corre-
sponding interrupt flag bit is set.
The instruction immediately following the SLEEP
instruction is executed on all exits by interrupt from Idle
or Sleep modes. Code execution then branches to the
interrupt vector if the GIE/GIEH bit of the INTCON reg-
ister is set, otherwise code execution continues without
branching (see Section 9.0 “Interrupts”).
A fixed delay of interval TCSD following the wake event
is required when leaving Sleep and Idle modes. This
delay is required for the CPU to prepare for execution.
Instruction execution resumes on the first clock cycle
following this delay.
3.5.2 EXIT BY WDT TIME-OUT
A WDT time-out will cause different actions depending
on which power-managed mode the device is in when
the time-out occurs.
If the device is not executing code (all Idle modes and
Sleep mode), the time-out will result in an exit from the
power-managed mode (see Section 3.2 “Run
Modes” and Section 3.3 “Sleep Mode”). If the device
is executing code (all Run modes), the time-out will
result in a WDT Reset (see Section 23.2 “Watchdog
Timer (WDT)”).
The WDT timer and postscaler are cleared by any one
of the following:
• executing a SLEEP instruction
• executing a CLRWDT instruction
• the loss of the currently selected clock source
when the Fail-Safe Clock Monitor is enabled
• modifying the IRCF bits in the OSCCON register
when the internal oscillator block is the device
clock source
3.5.3 EXIT BY RESET
Exiting Sleep and Idle modes by Reset causes code
execution to restart at address 0. See Section 4.0
“Reset” for more details.
The exit delay time from Reset to the start of code
execution depends on both the clock sources before
and after the wake-up and the type of oscillator. Exit
delays are summarized in Table 3-3.
DS41303G-page 48
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