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ST7LITEUS2, ST7LITEUS5
Power saving modes
49/136
8.2 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.
Slow mode is controlled by the SMS bit in the MCCSR register which enables or disables
Slow mode.
In this mode, the oscillator frequency is divided by 32. The CPU and peripherals are clocked
at this lower frequency.
Note:
Slow-wait mode is activated when entering Wait mode while the device is already in Slow
mode.
Figure 19.
Slow mode clock transition
8.3 Wait
mode
Wait mode places the MCU in a low power consumption mode by stopping the CPU.
This power saving mode is selected by calling the ‘WFI’ instruction.
All peripherals remain active. During Wait mode, the I bit of the CC register is cleared, to
enable all interrupts. All other registers and memory remain unchanged. The MCU remains
in Wait mode until an interrupt or reset occurs, whereupon the Program Counter branches to
the starting address of the interrupt or Reset service routine.
The MCU will remain in Wait mode until a Reset or an Interrupt occurs, causing it to wakeup.
Refer to
for a description of the Wait mode flowchart.
SMS
f
CPU
NORMAL RUN MODE
REQUEST
f
OSC
f
OSC
/32
f
OSC
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