STMicroelectronics STM32F05 series Reference Manual page 78

Power control (PWR)
Bit 2 CWUF: Clear wakeup flag.
This bit is always read as 0.
0: No effect
1: Clear the WUF Wakeup Flag after 2 System clock cycles. (write)
Bit 1 PDDS: Power down deepsleep.
This bit is set and cleared by software. It works together with the LPDS bit.
0: Enter Stop mode when the CPU enters Deepsleep. The regulator status depends on the
LPDS bit.
1: Enter Standby mode when the CPU enters Deepsleep.
Bit 0 LPDS: Low-power deepsleep.
This bit is set and cleared by software. It works together with the PDDS bit.
0: Voltage regulator on during Stop mode
1: Voltage regulator in low-power mode during Stop mode
Note: When a peripheral that can work in STOP mode requires a clock, the Power controller
78/742
automatically switch the voltage regulator from Low-power mode to Normal mode and
remains in this mode until the request disappears.
Doc ID 018940 Rev 1
RM0091