ST STM32F405 Reference Manual page 800

Real-time clock (RTC)
RTC_TAMP3
RTC_TAMP2
RTC_TAMP1
RTC_TS
RTC_REFIN
LSE (32.768 Hz)
HSE/32
LSI
RTCCLK
RTC_CALR
Smooth
calibration
WUCKSEL[1:0]
Prescaler
1, 2, 4, 8, 16
1. On STM32F4xx devices, the RTC_AF1 and RTC_AF2 alternate functions are connected to PC13 and PI8,
respectively.
800/1749
Figure 237. RTC block diagram
Backup registers
and RTC tamper
control register
ck_apre
RTC_PRER
(default 256 Hz
Asynchronous
7-bit prescaler
(default = 128)
RTC_WUTR
16-bit wakeup
auto reload timer
Alarm A
RTC_ALRMAR
RTC_ALRMASSR
Alarm B
RTC_ALRMBR
RTC_ALRMBSSR
RM0090 Rev 18
Time stamp
registers
ck_spre
RTC_PRER
(default 1 Hz)
Synchronous
15-bit prescaler
(default = 256)
Shadow registers
Shadow register
RTC_SSR
RTC_CALIB
RTC_ALARM
=
TAMPxF
TSF
Calendar
RTC_TR,
RTC_DR
Output
RTC_OUT
control
WUTF
OSEL[1:0]
ALRAF
=
ALRBF
RM0090
MS30216V6