Real-time clock (RTC) RM0090
653/1422 Doc ID 018909 Rev 4
23.6.10 RTC write protection register (RTC_WPR)
Address offset: 0x24
Reset value: 0x0000 0000
23.6.11 RTC sub second register (RTC_SSR)
Address offset: 0x28
Power-on reset value: 0x0000 0000
System reset: 0x0000 0000 when BYPSHAD = 0. Not affected when BYPSHAD = 1.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Reserved
1514131211109876543210
Reserved
KEY
wwwwwwww
Bits 31:8 Reserved, must be kept at reset value.
Bits 7:0 KEY: Write protection key
This byte is written by software.
Reading this byte always returns 0x00.
Refer to RTC register write protection for a description of how to unlock RTC register write
protection.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16
Reserved
rrrrrrrrrrrrrrrr
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
SS[15:0]
rrrr rrrrrrrrrr r r
Bits31:16 Reserved
Bits 15:0 SS: Sub second value
SS[15:0] is the value in the synchronous prescaler’s counter. The fraction of a second is
given by the formula below:
Second fraction = ( PREDIV_S - SS ) / ( PREDIV_S + 1 )
Note: SS can be larger than PREDIV_S only after a shift operation. In that case, the correct
time/date is one second less than as indicated by RTC_TR/RTC_DR.
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