pic24hj16gp304 Microchip Technology Inc., pic24hj16gp304 Datasheet - Page 94

• Manufacturer Part Number: pic24hj16gp304
• Description: High-performance, 16-bit Microcontrollers
• Manufacturer: Microchip Technology Inc.

PIC24HJ32GP202/204 and PIC24HJ16GP304
8.2.2
The following occur in Idle mode:
• The CPU stops executing instructions.
• The WDT is automatically cleared.
• The system clock source remains active. By
• If the WDT or FSCM is enabled, the LPRC also
The device will wake 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 begins immediately,
starting with the instruction following the PWRSAV
instruction, or the first instruction in the ISR.
8.2.3
Any interrupt that coincides with the execution of a
PWRSAV instruction is held off until entry into Sleep or
Idle mode is completed. The device then wakes up
from Sleep or Idle mode.
8.3
The preferred strategies for reducing power consump-
tion are changing clock speed and invoking one of the
power-saving modes. In some circumstances, how-
ever, these are not practical. For example, it may be
necessary for an application to maintain uninterrupted
synchronous communication, even while it is doing
nothing else. Reducing system clock speed can intro-
duce communication errors, while using a power-sav-
ing 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 contin-
ues 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.
DS70289A-page 92
default, all peripheral modules continue to operate
normally from the system clock source, but can
also be selectively disabled (see Section 8.4
“Peripheral Module Disable”).
remains active.
Doze Mode
IDLE MODE
INTERRUPTS COINCIDENT WITH
POWER SAVE INSTRUCTIONS
Preliminary
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>).
configurations, 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 inter-
rupt 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.
8.4
The Peripheral Module Disable (PMD) registers
provide a method to disable a peripheral module by
stopping all clock sources supplied to that module.
When a peripheral is disabled using the appropriate
PMD control bit, the peripheral is in a minimum power
consumption state. The control and status registers
associated with the peripheral are also disabled. So
writes to those registers will have no effect and read
values will be invalid.
A peripheral module is enabled only if both the associ-
ated bit in the PMD register are cleared and the periph-
eral is supported by the specific PIC24H variant. If the
peripheral is present in the device, it is enabled in the
PMD register by default.
Note:
Peripheral Module Disable
If a PMD bit is set, the corresponding mod-
ule is disabled after a delay of one instruc-
tion cycle. Similarly, if a PMD bit is
cleared, the corresponding module is
enabled after a delay of one instruction
cycle (assuming the module control regis-
ters are already configured to enable mod-
ule operation).
There
© 2007 Microchip Technology Inc.
are
eight
possible