Datasheet

dsPIC33FJ32GS406/606/608/610 and dsPIC33FJ64GS406/606/608/610
DS70591E-page 202  2009-2012 Microchip Technology Inc.
10.2.2 IDLE MODE
The following occur in Idle mode:
• The CPU stops executing instructions.
• The WDT is automatically cleared.
• The system clock source remains active. By
default, all peripheral modules continue to operate
normally from the system clock source, but can
also be selectively disabled (see Section 10.5
“Peripheral Module Disable”).
• If the WDT or FSCM is enabled, the LPRC also
remains active.
The device will wake-up from Idle mode on any of these
events:
• Any interrupt that is individually enabled
• Any device Reset
• A WDT time-out
On wake-up from Idle mode, the clock is reapplied to
the CPU and instruction execution will begin (2-4 clock
cycles later), starting with the instruction following the
PWRSAV instruction, or the first instruction in the ISR.
10.2.3 INTERRUPTS COINCIDENT WITH
POWER SAVE INSTRUCTIONS
Any interrupt that coincides with the execution of a
PWRSAV instruction is held off until entry into Sleep or
Idle mode has completed. The device then wakes up
from Sleep or Idle mode.
10.3 Doze Mode
The preferred strategies for reducing power
consumption are changing clock speed and invoking
one of the power-saving modes. In some circumstances,
this may not be practical. For example, it may be neces-
sary for an application to maintain uninterrupted
synchronous communication, even while it is doing noth-
ing else. Reducing system clock speed can introduce
communication errors, while using a power-saving mode
can stop communications completely.
Doze mode is a simple and effective alternative method
to reduce power consumption while the device is still
executing code. In this mode, the system clock
continues to operate from the same source and at the
same speed. Peripheral modules continue to be
clocked at the same speed, while the CPU clock speed
is reduced. Synchronization between the two clock
domains is maintained, allowing the peripherals to
access the SFRs while the CPU executes code at a
slower rate.
Doze mode is enabled by setting the DOZEN bit
(CLKDIV<11>). The ratio between peripheral and core
clock speed is determined by the DOZE<2:0> bits
(CLKDIV<14:12>). There are eight possible configura-
tions, from 1:1 to 1:128, with 1:1 being the default
setting.
Programs can use Doze mode to selectively reduce
power consumption in event-driven applications. This
allows clock-sensitive functions, such as synchronous
communications, to continue without interruption while
the CPU idles, waiting for something to invoke an
interrupt routine. An automatic return to full-speed CPU
operation on interrupts can be enabled by setting the
ROI bit (CLKDIV<15>). By default, interrupt events
have no effect on Doze mode operation.
For example, suppose the device is operating at
20 MIPS and the CAN module has been configured for
500 kbps based on this device operating speed. If the
device is placed in Doze mode with a clock frequency
ratio of 1:4, the CAN module continues to communicate
at the required bit rate of 500 kbps, but the CPU now
starts executing instructions at a frequency of 5 MIPS.
10.4 PWM Power-Saving Features
Typically, many applications need either a high-
resolution duty cycle or phase offset (for fixed
frequency operation) or a high-resolution PWM period
for variable frequency modes of operation (such as
Resonant mode). Very few applications require both
high-resolution modes simultaneously.
The HRPDIS and the HRDDIS bits in the AUXCONx
registers permit the user to disable the circuitry associ-
ated with the high-resolution duty cycle and PWM
period to reduce the operating current of the device.
If the HRDDIS bit is set, the circuitry associated with
the high-resolution duty cycle, phase offset, and dead
time for the respective PWM generator is disabled. If
the HRPDIS bit is set, the circuitry associated with the
high-resolution PWM period for the respective PWM
generator is disabled.
When the HRPDIS bit is set, the smallest unit of
measure for the PWM period is 8.32 ns.
If the HRDDIS bit is set, the smallest unit of measure
for the PWM duty cycle, phase offset and dead time is
8.32 ns.