Real-time clock (RTC) RM0351
1066/1693 DocID024597 Rev 3
The RTC includes:
• Two alarms
• Three tamper events
• 32 x 32-bit backup registers
– The backup registers (RTC_BKPxR) are implemented in the RTC domain that
remains powered-on by VBAT when the VDD power is switched off.
• Alternate function outputs: RTC_OUT which selects one of the following two outputs:
– RTC_CALIB: 512 Hz or 1Hz clock output (with an LSE frequency of 32.768 kHz).
This output is enabled by setting the COE bit in the RTC_CR register.
– RTC_ALARM: This output is enabled by configuring the OSEL[1:0] bits in the
RTC_CR register which select the Alarm A, Alarm B or Wakeup outputs.
• Alternate function inputs:
– RTC_TS: timestamp event
– RTC_TAMP1: tamper1 event detection
– RTC_TAMP2: tamper2 event detection
– RTC_TAMP3: tamper3 event detection
– RTC_REFIN: 50 or 60 Hz reference clock input
34.3.2 GPIOs controlled by the RTC
RTC_OUT, RTC_TS and RTC_TAMP1 are mapped on the same pin (PC13). PC13 pin
configuration is controlled by the RTC, whatever the PC13 GPIO configuration. The RTC
functions mapped on PC13 are available in all low-power modes and in VBAT mode.
The output mechanism follows the priority order shown in Table 170.
Table 170. RTC pin PC13 configuration
(1)
PC13 Pin
configuration
and function
OSEL[1:0]
bits
(RTC_ALARM
output
enable)
COE bit
(RTC_CALIB
output
enable)
RTC_OUT
_RMP
bit
RTC_ALARM
_TYPE
bit
TAMP1E bit
(RTC_TAMP1
input
enable)
TSE bit
(RTC_TS
input
enable)
RTC_ALARM
output OD
01 or 10 or 11 Don’t care
0
0 Don’t care Don’t care
1
RTC_ALARM
output PP
01 or 10 or 11 Don’t care
0
1 Don’t care Don’t care
1
RTC_CALIB
output PP
00 1 0 Don’t care Don’t care Don’t care
RTC_TAMP1
input floating
00 0 Don’t care
Don’t care 1 000 1
1
01 or 10 or 11 0
RTC_TS and
RTC_TAMP1
input floating
00 0 Don’t care
Don’t care 1 100 1
1
01 or 10 or 11 0
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