DocID024597 Rev 3 1067/1693
RM0351 Real-time clock (RTC)
1106
In addition, it is possible to remap RTC_OUT on PB2 pin thanks to RTC_OUT_RMP bit. In
this case it is mandatory to configure PB2 GPIO registers as alternate function with the
correct type. The remap functions are shown in Table 171.
34.3.3 Clock and prescalers
The RTC clock source (RTCCLK) is selected through the clock controller among the LSE
clock, the LSI oscillator clock, and the HSE clock. For more information on the RTC clock
source configuration, refer to Section 6: Reset and clock control (RCC).
A programmable prescaler stage generates a 1 Hz clock which is used to update the
calendar. To minimize power consumption, the prescaler is split into 2 programmable
prescalers (see Figure 351: RTC block diagram):
• A 7-bit asynchronous prescaler configured through the PREDIV_A bits of the
RTC_PRER register.
• A 15-bit synchronous prescaler configured through the PREDIV_S bits of the
RTC_PRER register.
RTC_TS input
floating
00 0 Don’t care
Don’t care 0 100 1
1
01 or 10 or 11 0
Wakeup pin or
Standard
GPIO
00 0 Don’t care
Don’t care 0 000 1
1
01 or 10 or 11 0
1. OD: open drain; PP: push-pull.
Table 170. RTC pin PC13 configuration
(1)
(continued)
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)
Table 171. RTC_OUT mapping
OSEL[1:0] bits
(RTC_ALARM
output enable)
COE bit
(RTC_CALIB
output enable)
RTC_OUT_RMP
bit
RTC_OUT on
PC13
RTC_OUT on
PB2
00 0
0
--
00 1 RTC_CALIB -
01 or 10 or 11 Don’t care RTC_ALARM -
00 0
1
--
00 1 - RTC_CALIB
01 or 10 or 11 0 - RTC_ALARM
01 or 10 or 11 1 RTC_ALARM RTC_CALIB
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