STM32F105RBT6 INTERNAL RTC CLOCK SHIFT FROM LSE TO LSI

[DeepakKumar]

Hi ST Team,

                    Currently i am using STM32F105RBT6 in our project. In this project i am using microcontroller internal RTC module to monitor the time with LSE clock for RTC run. When the LSE crystal(32.768) is not mounted in our PCB then microcontroller stuck in SystemClock_Config() function & program control is not come in while loop.

We need a solution in which when LSE crystal is not mounted on PCB  then controller shift its RTC clock to LSI & come in while loop to execute instruction. 

Please help me to resolve this issue.

Thanks with Regards

Deepak

Embedded Enginner

[waclawek.jan]

- set RCC_BDCR.LSEON to enable LSE

- wait for RCC_BDCR.LSERDY to get being set, indicating that LSE is running; but for that wait use some sort of timeout - it can be a single loop counter, with number of counts selected so that it times out only after a reasonable LSE startup time (which can be up to 10 seconds)

- if timeout occured and RCC_BDCR.LSERDY is not set, it means, that the crystal is not mounted, so then you start LSI by setting RCC_CSR.LSION and waiting until RCC_CSR.LSIRDY is set

- only after that select RTC clock accordingly to whether LSE or LSI is running, in RCC_BDCR.RTCSEL, and then set up RTC itself

You have to be aware of the fact that LSI is very imprecise and not suitable for maintaining real-time.

If you have battery installed at VBAT, the procedure may be slightly different, with checking whether LSE already runs at the beginning.

JW