PIC24H datasheet(135/290 Pages) MICROCHIP

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Preliminary

DS70175D-page 135

PIC24H

9.0

POWER-SAVING FEATURES

The PIC24H 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 cir-

cuits being clocked constitutes lower consumed power.

PIC24H 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

PIC24H devices allow a wide range of clock frequen-

cies 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

PIC24H 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 assembly 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

Sleep mode has these features:

• 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

during Sleep mode 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 in Sleep mode. 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 in Sleep mode.

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, the processor restarts with the

same clock source that was active when Sleep mode

was entered.

EXAMPLE 9-1:

PWRSAV

INSTRUCTION SYNTAX

Note:

This data sheet summarizes the features

of this group of PIC24H devices. It is not

intended to be a comprehensive reference

source. To complement the information in

this data sheet, refer to the “dsPIC30F

Family Reference Manual” (DS70046).

Note:

SLEEP_MODE and IDLE_MODE are

constants

defined

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

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