DocID018909 Rev 11
817/1731
RM0090
Real-time clock (RTC)
828
Note:
This register can be written only when ALRBWF is set to 1 in RTC_ISR, or in initialization
mode.
This register is write protected. The write access procedure is described in
26.6.10 RTC write protection register (RTC_WPR)
Address offset: 0x24
Backup domain reset value: 0x0000 0000
26.6.11
RTC sub second register (RTC_SSR)
Address offset: 0x28
Backup domain 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
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Reserved
KEY
w
w
w
w
w
w
w
w
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
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
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
SS[15:0]
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
r
Bits 31:16 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 ) / ( PR 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.