Datasheet

PIC18(L)F2X/4XK22
DS40001412G-page 44  2010-2016 Microchip Technology Inc.
3.0 POWER-MANAGED MODES
PIC18(L)F2X/4XK22 devices offer a total of seven
operating modes for more efficient power
management. These modes provide a variety of
options for selective power conservation in applications
where resources may be limited (i.e., battery-powered
devices).
There are three categories of power-managed modes:
• Run modes
• Idle modes
• Sleep mode
These categories define which portions of the device
are clocked and sometimes, what speed. The Run and
Idle modes may use any of the three available clock
sources (primary, secondary or internal oscillator
block). The Sleep mode does not use a clock source.
The power-managed modes include several power-
saving features offered on previous PIC
®
microcontroller
devices. One of the clock switching features allows the
controller to use the secondary oscillator (SOSC) in
place of the primary oscillator. Also included is the Sleep
mode, offered by all PIC microcontroller devices, where
all device clocks are stopped.
3.1 Selecting Power-Managed Modes
Selecting a power-managed mode requires two
decisions:
• Whether or not the CPU is to be clocked
• The selection of a clock source
The IDLEN bit (OSCCON<7>) controls CPU clocking,
while the SCS<1:0> bits (OSCCON<1:0>) select the
clock source. The individual modes, bit settings, clock
sources and affected modules are summarized in
Table 3-1.
3.1.1 CLOCK SOURCES
The SCS<1:0> bits allow the selection of one of three
clock sources for power-managed modes. They are:
• the primary clock, as defined by the FOSC<3:0>
Configuration bits
• the secondary clock (the SOSC oscillator)
• the internal oscillator block
3.1.2 ENTERING POWER-MANAGED
MODES
Switching from one power-managed mode to another
begins by loading the OSCCON register. The
SCS<1:0> bits select the clock source and determine
which Run or Idle mode is to be used. Changing these
bits causes an immediate switch to the new clock
source, assuming that it is running. The switch may
also be subject to clock transition delays. Refer to
Section 2.11 “Clock Switching” for more information.
Entry to the power-managed Idle or Sleep modes is
triggered by the execution of a SLEEP instruction. The
actual mode that results depends on the status of the
IDLEN bit.
Depending on the current mode and the mode being
switched to, a change to a power-managed mode does
not always require setting all of these bits. Many
transitions may be done by changing the oscillator select
bits, or changing the IDLEN bit, prior to issuing a SLEEP
instruction. If the IDLEN bit is already configured
correctly, it may only be necessary to perform a SLEEP
instruction to switch to the desired mode.
TABLE 3-1: POWER-MANAGED MODES
Mode
OSCCON Bits Module Clocking
Available Clock and Oscillator Source
IDLEN
(1)
SCS<1:0> CPU Peripherals
Sleep 0 N/A Off Off None – All clocks are disabled
PRI_RUN N/A 00 Clocked Clocked Primary – LP, XT, HS, RC, EC and Internal
Oscillator Block
(2)
.
This is the normal full-power execution mode.
SEC_RUN N/A 01 Clocked Clocked Secondary – SOSC Oscillator
RC_RUN N/A 1x Clocked Clocked Internal Oscillator Block
(2)
PRI_IDLE 100Off Clocked Primary – LP, XT, HS, HSPLL, RC, EC
SEC_IDLE 101Off Clocked Secondary – SOSC Oscillator
RC_IDLE 11xOff Clocked Internal Oscillator Block
(2)
Note 1: IDLEN reflects its value when the SLEEP instruction is executed.
2: Includes HFINTOSC and HFINTOSC postscaler, as well as the LFINTOSC source.