ST STM32L4+ Series Reference Manual page 1568

Real-time clock (RTC) applied to STM32L4Rxxx and STM32L4Sxxx only
Bit 17 SUB1H: Subtract 1 hour (winter time change)
When this bit is set, 1 hour is subtracted to the calendar time if the current hour is not 0. This
bit is always read as 0.
Setting this bit has no effect when current hour is 0.
Bit 16 ADD1H: Add 1 hour (summer time change)
When this bit is set, 1 hour is added to the calendar time. This bit is always read as 0.
Bit 15 TSIE: Time-stamp interrupt enable
Bit 14 WUTIE: Wakeup timer interrupt enable
Bit 13 ALRBIE: Alarm B interrupt enable
Bit 12 ALRAIE: Alarm A interrupt enable
Bit 11 TSE: timestamp enable
Bit 10 WUTE: Wakeup timer enable
Note: When the wakeup timer is disabled, wait for WUTWF=1 before enabling it again.
Bit 9 ALRBE: Alarm B enable
Bit 8 ALRAE: Alarm A enable
Bit 7 Reserved, must be kept at reset value.
Bit 6 FMT: Hour format
1568/2301
0: No effect
1: Subtracts 1 hour to the current time. This can be used for winter time change outside
initialization mode.
0: No effect
1: Adds 1 hour to the current time. This can be used for summer time change outside
initialization mode.
0: Time-stamp Interrupt disable
1: Time-stamp Interrupt enable
0: Wakeup timer interrupt disabled
1: Wakeup timer interrupt enabled
0: Alarm B Interrupt disable
1: Alarm B Interrupt enable
0: Alarm A interrupt disabled
1: Alarm A interrupt enabled
0: timestamp disable
1: timestamp enable
0: Wakeup timer disabled
1: Wakeup timer enabled
0: Alarm B disabled
1: Alarm B enabled
0: Alarm A disabled
1: Alarm A enabled
0: 24 hour/day format
1: AM/PM hour format
RM0432 Rev 6
RM0432