PIC18F2420/2520/4420/4520
3.3
Sleep Mode
3.4
Idle Modes
The power-managed Sleep mode in the PIC18F2420/
2520/4420/4520 devices is identical to the legacy
Sleep mode offered in all other PIC devices. It is
entered by clearing the IDLEN bit (the default state on
device Reset) and executing the SLEEP instruction.
This shuts down the selected oscillator (Figure 3-5). All
clock source status bits are cleared.
The Idle modes allow the controller’s CPU to be
selectively shut down while the peripherals continue to
operate. Selecting a particular Idle mode allows users
to further manage power consumption.
If the IDLEN bit is set to ‘1’ when a SLEEPinstruction is
executed, the peripherals will be clocked from the clock
source selected using the SCS<1:0> bits; however, the
CPU will not be clocked. The clock source status bits are
not affected. Setting IDLEN and executing a SLEEP
instruction provides a quick method of switching from a
given Run mode to its corresponding Idle mode.
Entering the Sleep mode from any other mode does not
require a clock switch. This is because no clocks are
needed once the controller has entered Sleep. If the
WDT is selected, the INTRC source will continue to
operate. If the Timer1 oscillator is enabled, it will also
continue to run.
If the WDT is selected, the INTRC source will continue
to operate. If the Timer1 oscillator is enabled, it will also
continue to run.
When a wake event occurs in Sleep mode (by interrupt,
Reset or WDT time-out), the device will not be clocked
until the clock source selected by the SCS<1:0> bits
becomes ready (see Figure 3-6), or it will be clocked
from the internal oscillator block if either the Two-Speed
Start-up or the Fail-Safe Clock Monitor are enabled
(see Section 23.0 “Special Features of the CPU”). In
either case, the OSTS bit is set when the primary clock
is providing the device clocks. The IDLEN and SCS bits
are not affected by the wake-up.
Since the CPU is not executing instructions, the only
exits from any of the Idle modes are by interrupt, WDT
time-out or a Reset. When a wake event occurs, CPU
execution is delayed by an interval of TCSD
(parameter 38, Table 26-10) while it becomes ready to
execute code. When the CPU begins executing code,
it resumes with the same clock source for the current
Idle mode. For example, when waking from RC_IDLE
mode, the internal oscillator block will clock the CPU
and peripherals (in other words, RC_RUN mode). The
IDLEN and SCS bits are not affected by the wake-up.
While in any Idle mode or the Sleep mode, a WDT
time-out will result in a WDT wake-up to the Run mode
currently specified by the SCS1:SCS0 bits.
FIGURE 3-5:
TRANSITION TIMING FOR ENTRY TO SLEEP MODE
Q1 Q2 Q3 Q4 Q1
OSC1
CPU
Clock
Peripheral
Clock
Sleep
Program
Counter
PC
PC + 2
FIGURE 3-6:
TRANSITION TIMING FOR WAKE FROM SLEEP (HSPLL)
Q3 Q4 Q1 Q2 Q3 Q4 Q1 Q2 Q3 Q4
Q2 Q3 Q4 Q1 Q2
Q1
OSC1
(1)
(1)
TOST
TPLL
PLL Clock
Output
CPU Clock
Peripheral
Clock
Program
Counter
PC
PC + 2
PC + 4
PC + 6
Wake Event
Note1: TOST = 1024 TOSC; TPLL = 2 ms (approx). These intervals are not shown to scale.
OSTS bit Set
© 2008 Microchip Technology Inc.
Advance Information
DS39631E-page 37
MICROCHIP [ MICROCHIP ]
