ST STM32F301 6 Series Reference Manual page 623

RM0366
Bits 15:13 WDU[2:0]: Week day units
Bit 12 MT: Month tens in BCD format
Bits 11:8 MU[3:0]: Month units in BCD format
Bits 7:6 Reserved, must be kept at reset value.
Bits 5:4 DT[1:0]: Date tens in BCD format
Bits 3:0 DU[3:0]: Date units in BCD format
000: forbidden
001: Monday
...
111: Sunday
RM0366 Rev 5
Real-time clock (RTC)
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