RM0402 Rev 6 619/1163
RM0402 Real-time clock (RTC)
655
– 0.95 ppm accuracy, obtained in a calibration window of several seconds
• Timestamp function for event saving (1 event)
• Tamper detection:
– 2 tamper events with configurable filter and internal pull-up.
• 20 backup registers (80 bytes). The backup registers are reset when a tamper
detection event occurs.
• Alternate function output (RTC_OUT) which selects one of the following two outputs:
– RTC_CALIB: 512 Hz or 1 Hz clock output (with an LSE frequency of 32.768 kHz).
This output is enabled by setting the COE bit in the RTC_CR register. It is routed
to the device RTC_AF1 function.
– RTC_ALARM (Alarm A, Alarm B or wakeup).
This output is selected by configuring the OSEL[1:0] bits in the RTC_CR register.
It is routed to the device RTC_AF1 function.
• RTC alternate function inputs:
– RTC_TS: timestamp event detection. It is routed to the device RTC_AF1.
– RTC_TAMP1: TAMPER1 event detection. It is routed to the device RTC_AF1.
– RTC_REFIN: reference clock input (usually the mains, 50 or 60 Hz).
Figure 207. RTC block diagram
MSv39307V2
Ck_apre
(default 256 Hz)
RTC_CALIB
512 Hz
RTC_WUTR
RTCCLK
WUTF
HSE_RTC
(4 MHz max)
LSE
(32.768 Hz)
LSI
Synchronous
15-bit prescaler
(default = 256)
Calendar
Prescaler
/ 2, 4, 8, 16
16-bit wakeup
auto-reload timer
Alarm A
(RTC_ALRMAR,
RTC_ALRMASSR
registers)
ALRAF
RTC_ALARM
RT C_PR E R
RTC_PRER
Coarse
calibration
RTC_CAL
IBR
==
ALRBF
Time
stamp
registers
TSF
Output
control
RTC_AF1
RTC_OUT
Smooth
Calibration
RTC_CAL
R
1 Hz
=
Alarm B
(RTC_ALRMBR,
RTC_ALRMBSSR
registers)
WUCKSEL[1:0]
Backup and
RTC tamper
control
registers
RTC_TAMP1
RTC_TS
TAMPE
TSE
Shadow
Registers
(RTC_SSR)
Shadow
Registers
(RTC_TR/DR)
ck_spre
(default
1 Hz)
Asynchronous
7-bit prescaler
(default = 128)
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