Datasheet

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ST7LITE20F2 ST7LITE25F2 ST7LITE29F2 Power saving modes
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9 Power saving modes
9.1 Introduction
To give a large measure of flexibility to the application in terms of power consumption, five
main power saving modes are implemented in the ST7 (see Figure 21):
• Slow
• Wait (and Slow-Wait)
• Active Halt
• Auto Wake up From Halt (AWUF)
• Halt
After a RESET the normal operating mode is selected by default (Run mode). This mode
drives the device (CPU and embedded peripherals) by means of a master clock which is
based on the main oscillator frequency divided or multiplied by 2 (f
OSC2
).
From RUN mode, the different power saving modes may be selected by setting the relevant
register bits or by calling the specific ST7 software instruction whose action depends on the
oscillator status.
Figure 21. Power saving mode transitions
9.2 SLOW mode
This mode has two targets:
• To reduce power consumption by decreasing the internal clock in the device,
• To adapt the internal clock frequency (f
CPU
) to the available supply voltage.
POWER CONSUMPTION
WAIT
SLOW
RUN
ACTIVE-HALT
HIGH
LOW
SLOW-WAIT
AUTO-WAKEUP FROM HALT
HALT