XC886/888CLM
Power Saving Modes
User’s Manual
8-3
V1.3, 2010-02
Power Saving Modes, V 1.0
routine or at any point in the program where the user no longer requires the slow-
down mode.
•
The other way of terminating the combined idle and slow-down mode is through a
hardware reset.
8.1.3
Power-down Mode
In power-down mode, the oscillator and the PLL are turned off. The FLASH is put into
the power-down mode. The main voltage regulator is switched off, but the low power
voltage regulator continues to operate. Therefore, all functions of the microcontroller are
stopped and only the contents of the FLASH, on-chip RAM, XRAM and the SFRs are
maintained. The port pins hold the logical state they had when the power-down mode
was activated. For the digital ports, the user must take care that the ports are not floating
in power-down mode. This can be done with internal or external pull-up/pull-down or
putting the port to output.
In power-down mode, the clock is turned off. Hence, it cannot be awakened by an
interrupt or by the WDT. It is awakened only when it receives an external wake-up signal
or reset signal.
Entering Power-down Mode
Software requests power-down mode by setting the bit PMCON0.PD to 1.
Two NOP instructions must be inserted after the bit PMCON0.PD is set to 1. This
ensures the first instruction (after two NOP instructions) is executed correctly after wake-
up from power-down mode.
If the external wake-up from power-down is used, software must prepare the external
environment of the XC886/888 to trigger one of these signals under the appropriate
conditions before entering power-down mode. A wake-up circuit is used to detect a
wake-up signal and activate the power-up. During power-down, this circuit remains
active. It does not depend on any clocks. Exit from power-down mode can be achieved
by applying a falling edge trigger to the:
•
EXINT0 pin
•
RXD pin
•
RXD pin or EXINT0 pin
The wake-up source can be selected by the bit WS of the PMCON0 register. The
wake-up with reset or without reset is selected by bit PMCON0.WKSEL. The wake-up
source and wake-up type must be selected before the system enters the power-down
mode.
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