Datasheet

© 2007-2011 Microchip Technology Inc. DS70265E-page 113
dsPIC33FJ12MC201/202
9.0 POWER-SAVING FEATURES
The dsPIC33FJ12MC201/202 devices provide the
ability to manage power consumption by selectively
managing clocking to the CPU and the peripherals. In
general, a lower clock frequency and a reduction in the
number of circuits being clocked constitutes lower
consumed power. dsPIC33FJ12MC201/202 devices
can manage power consumption in four different ways:
• Clock frequency
• Instruction-based Sleep and Idle modes
• Software-controlled Doze mode
• Selective peripheral control in software
Combinations of these methods can be used to selec-
tively tailor an application’s power consumption while
still maintaining critical application features, such as
timing-sensitive communications.
9.1 Clock Frequency and Clock
Switching
dsPIC33FJ12MC201/202 devices allow a wide range
of clock frequencies to be selected under application
control. If the system clock configuration is not locked,
users can choose low-power or high-precision
oscillators by simply changing the NOSC bits
(OSCCON<10:8>). The process of changing a system
clock during operation, as well as limitations to the
process, are discussed in more detail in Section 8.0
“Oscillator Configuration”.
9.2 Instruction-Based Power-Saving
Modes
dsPIC33FJ12MC201/202 devices have two special
power-saving modes that are entered through the
execution of a special PWRSAV instruction. Sleep mode
stops clock operation and halts all code execution. Idle
mode halts the CPU and code execution, but allows
peripheral modules to continue operation. The
assembler syntax of the PWRSAV instruction is shown in
Example 9-1.
Sleep and Idle modes can be exited as a result of an
enabled interrupt, WDT time-out or a device Reset. When
the device exits these modes, it is said to wake-up.
9.2.1 SLEEP MODE
The following occur in Sleep mode:
• The system clock source is shut down. If an
on-chip oscillator is used, it is turned off.
• The device current consumption is reduced to a
minimum, provided that no I/O pin is sourcing
current
• The Fail-Safe Clock Monitor does not operate,
since the system clock source is disabled
• The LPRC clock continues to run in Sleep mode if
the WDT is enabled
• The WDT, if enabled, is automatically cleared
prior to entering Sleep mode
• Some device features or peripherals may continue
to operate. This includes items such as the input
change notification on the I/O ports, or peripherals
that use an external clock input.
• Any peripheral that requires the system clock
source for its operation is disabled
The device will wake-up from Sleep mode on any of the
these events:
• Any interrupt source that is individually enabled
• Any form of device Reset
• A WDT time-out
On wake-up from Sleep mode, the processor restarts
with the same clock source that was active when Sleep
mode was entered.
EXAMPLE 9-1: PWRSAV INSTRUCTION SYNTAX
Note 1: This data sheet summarizes the features
of the dsPIC33FJ12MC201/202 family of
devices. It is not intended to be a
comprehensive reference source. To
complement the information in this data
sheet, refer to Section 9. “Watchdog
Timer and Power-Saving Modes”
(DS70196) of the “dsPIC33F/PIC24H
Family Reference Manual”, which is
available from the Microchip website
(www.microchip.com).
2: Some registers and associated bits
described in this section may not be
available on all devices. Refer to
Section 4.0 “Memory Organization” in
this data sheet for device-specific register
and bit information.
Note: SLEEP_MODE and IDLE_MODE are
constants defined in the assembler
include file for the selected device.
PWRSAV #SLEEP_MODE ; Put the device into Sleep mode
PWRSAV #IDLE_MODE ; Put the device into Idle mode