Clock And Prescalers; Table 78. Lse Pin Pc14 Configuration; Table 79. Lse Pin Pc15 Configuration - STMicroelectronics STM32F05 series Reference Manual

Real-time clock (RTC)
Table 78. LSE pin PC14 configuration
Pin configuration and
function
LSE oscillator
LSE bypass
Output PP forced
Standard GPIO
1. OD: open drain; PP: push-pull.
Table 79. LSE pin PC15 configuration
Pin configuration and
function
LSE oscillator
Output PP forced
Standard GPIO
1. OD: open drain; PP: push-pull.
24.3.3

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 the Reset and clock control (RCC) section.
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
●
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.
Note: When both prescalers are used, it is recommended to configure the asynchronous prescaler
to a high value to minimize consumption.
538/742
(1)
LSEON bit in
RCC_BDCR register
1
1
0
0
(1)
LSEON bit in
RCC_BDCR register
1
1
0
0
Figure 227: RTC block
Doc ID 018940 Rev 1
LSEBYP bit in
RCC_BDCR register
0
1
Don't care
Don't care
LSEBYP bit in
RCC_BDCR register
0
1
Don't care
Don't care
diagram):
PC14MODE PC14VALUE
bit
Don't care Don't care
Don't care Don't care
PC14 output data
1
value
0 Don't care
PC15MODE PC15VALUE
bit
Don't care Don't care
PC15 output data
1
value
0 Don't care
RM0091
bit
bit