ST STM32F405 Reference Manual page 834

Real-time clock (RTC)
Bit 1 TAMP1TRG: Active level for tamper 1
Caution: When TAMPFLT = 0, TAMPxE must be reset when TAMPxTRG is changed to avoid
Bit 0 TAMP1E: Tamper 1 detection enable
26.6.18 RTC alarm A sub second register (RTC_ALRMASSR)
Address offset: 0x44
Backup domain reset value: 0x0000 0000
System reset: not affected
31 30 29
Reserved
r r r
15 14 13
Reserved
r rw rw
Bits 31:28 Reserved
Bits 27:24 MASKSS[3:0]: Mask the most-significant bits starting at this bit
Bits 23:15 Reserved
Bits 14:0 SS[14:0]: Sub seconds value
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if TAMPFLT != 00
0: TAMPER1 staying low triggers a tamper detection event.
1: TAMPER1 staying high triggers a tamper detection event.
if TAMPFLT = 00:
0: TAMPER1 rising edge triggers a tamper detection event.
1: TAMPER1 falling edge triggers a tamper detection event.
spuriously setting TAMPxF.
0: Tamper 1 detection disabled
1: Tamper 1 detection enabled
28 27 26 25
MASKSS[3:0]
r rw rw rw
12 11 10 9
rw rw rw rw
0: No comparison on sub seconds for Alarm A. The alarm is set when the seconds unit is
incremented (assuming that the rest of the fields match).
1: SS[14:1] are don't care in Alarm A comparison. Only SS[0] is compared.
2: SS[14:2] are don't care in Alarm A comparison. Only SS[1:0] are compared.
3: SS[14:3] are don't care in Alarm A comparison. Only SS[2:0] are compared.
...
12: SS[14:12] are don't care in Alarm A comparison. SS[11:0] are compared.
13: SS[14:13] are don't care in Alarm A comparison. SS[12:0] are compared.
14: SS[14] is don't care in Alarm A comparison. SS[13:0] are compared.
15: All 15 SS bits are compared and must match to activate alarm.
The overflow bits of the synchronous counter (bits 15) is never compared. This bit can be
different from 0 only after a shift operation.
This value is compared with the contents of the synchronous prescaler's counter to
determine if Alarm A is to be activated. Only bits 0 up MASKSS-1 are compared.
24 23 22
rw r r
8 7 6
SS[14:0]
rw rw rw
RM0090 Rev 18
21 20 19 18
Reserved
r r r r
5 4 3 2
rw rw rw w
RM0090
17 16
r r
1 0
rw rw