STM32F103 several special pins are used as ordinary io. Precautions and data loss of backup register 1,2

stm32F103C8T6 chip  

There are two possibilities for backup register data loss :

1、 Triggered an intrusion interrupt

PC13 As an ordinary IO When using To disable the intrusion interrupt function , Otherwise, the backup register data will be shut down , Data loss at startup ,( You can check other articles , Don't explain in detail )

2、  chip VBAT Power off when the machine is turned off . If you need to back up the register to save data when it is shut down , that VBAT Need to connect to button battery , If after shutdown VBAT Also power down , Backup registers cannot be saved , At that time, I was curious about why the backup register data was always lost , It turns out that VBAT Why , Later it was changed to flash Stored data , practice : Triggered when shutdown Low voltage interruption , Then save the data to flash.( It's usually used MCU Inside flash For storage ,100uF enough 512 Byte storage )

 

The following is a description of several special pins :

1、PC13   RTC

Introduction to intrusion function :

  Intrusion detection function analysis ： Functional data backup .

1 BKP_CR Of TPAL position , Set the decision TAMPER The signal of the pin is determined by 0 change 1 Or another 1 change 0 Is a valid trigger signal , Generate intrusion detection event set flag position (BKR_CSR Of TEF).

2 After the intrusion detection event, all data backup registers will be reset .

3 One thing to notice is that ： stay BKP_CR Of TPE Bit allows before enabling , An intrusion detection event generated by an intrusion detection pin is also effective . This is beneficial For better protection of data .

4. When TPAL=0( or 1), If you are in BKP_CR Of TPE Bit permission （ Intrusion detection pin allows bit ） Before enabling TPAL=1( or 0), Once the intrusion detection function is allowed , An additional intrusion event will occur . Even though BKP_CR Of TPE（ Intrusion detection pin allows bit ） Position as 1 Then there is a new edge jump

5 After an intrusion detection event is detected and cleared , Intrusion detection pin should be prohibited . Reset before writing the data backup register again BKP_CR Of TPE position （ Intrusion detection pin allows bit ）. In this way, it can avoid the intrusion detection event still occurring on the intrusion detection pin , Keep writing to the data backup register .

6VDD When the power supply is disconnected , Intrusion detection function is still valid , Bit to avoid unnecessary data backup register reset ,TAMPER The outside of the pin should be connected to the correct level .

 

initialization IO Add this full stop when :     

      PWR_BackupAccessCmd( ENABLE );/* Allow modification of RTC And backup registers */
     RCC_LSEConfig(RCC_LSE_OFF);// Turn off the external low-speed external clock signal function after ,PC13 PC14 PC15 Can be ordinary IO use .
     BKP_TamperPinCmd(DISABLE);  /* Turn off intrusion detection ,PC13 Can be used as ordinary IO*/
     BKP_ITConfig(DISABLE);       /* prohibit TAMPER interrupt */

 

2、 PA13  PA14  PA15    These three feet are   JTAG foot , Even according to ordinary IO Initialization is also not normal. You need to add

    GPIO_PinRemapConfig(GPIO_Remap_SWJ_JTAGDisable , ENABLE);

It can be regarded as normal IO Use