ST STM32L4 5 Series Reference Manual page 1216

Real-time clock (RTC)
38.6.8 RTC alarm B register (RTC_ALRMBR)
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
write protection on page
Address offset: 0x20
Backup domain reset value: 0x0000 0000
System reset: not affected
31 30 29
MSK4 WDSEL DT[1:0]
rw rw rw
15 14 13
MSK2 MNT[2:0]
rw rw rw
Bit 31 MSK4: Alarm B date mask
0: Alarm B set if the date and day match
1: Date and day don't care in Alarm B comparison
Bit 30 WDSEL: Week day selection
0: DU[3:0] represents the date units
1: DU[3:0] represents the week day. DT[1:0] is don't care.
Bits 29:28 DT[1:0]: Date tens in BCD format
Bits 27:24 DU[3:0]: Date units or day in BCD format
Bit 23 MSK3: Alarm B hours mask
0: Alarm B set if the hours match
1: Hours don't care in Alarm B comparison
Bit 22 PM: AM/PM notation
0: AM or 24-hour format
1: PM
Bits 21:20 HT[1:0]: Hour tens in BCD format
Bits 19:16 HU[3:0]: Hour units in BCD format
Bit 15 MSK2: Alarm B minutes mask
0: Alarm B set if the minutes match
1: Minutes don't care in Alarm B comparison
Bits 14:12 MNT[2:0]: Minute tens in BCD format
Bits 11:8 MNU[3:0]: Minute units in BCD format
Bit 7 MSK1: Alarm B seconds mask
0: Alarm B set if the seconds match
1: Seconds don't care in Alarm B comparison
Bits 6:4 ST[2:0]: Second tens in BCD format
Bits 3:0 SU[3:0]: Second units in BCD format
1216/1830
1193.
28 27 26 25
DU[3:0]
rw rw rw rw
12 11 10 9
MNU[3:0]
rw rw rw rw
DocID024597 Rev 5
24 23 22 21
MSK3 PM HT[1:0]
rw rw rw rw
8 7 6 5
MSK1 ST[2:0]
rw rw rw rw
RM0351
RTC register
20 19 18 17
HU[3:0]
rw rw rw rw
4 3 2 1
SU[3:0]
rw rw rw rw
16
rw
0
rw