Application principle of STM32 BOOT0 and BOOT1

When many netizens use Keil to download programs, the download line is connected normally, but the program cannot be downloaded, and it prompts that the chip is not connected. The possible cause of the error is BOOT0.

First, let’s introduce how BOOT0 and BOOT1 are connected and the connection method.

Application principle of BOOT0 and BOOT1 of STM32 microcontroller
The storage media corresponding to the three boot modes of STM32 are all built-in chips, which are:
1) Main flash memory = Flash built into the chip. This is also the normal working mode
2) SRAM = RAM area built into the chip, that is, memory.
3) System memory = A specific area inside the chip. A Bootloader is preset in this area when the chip leaves the factory, which is usually called
ISP program. No one can modify or erase the content of this area after the chip leaves the factory, that is, it is a ROM area.
There are two pins BOOT0 and BOOT1 on each STM32 chip. The level state of these two pins when the chip is reset determines the chip reset.

After the bit is set, the program will be executed from which area, see the following table:

It should be noted that the built-in SRAM is generally not used for startup (BOOT1=1 BOOT0=1), because the data
in the SRAM will be lost after power failure. In most cases, SRAM is only used for debugging, and it can also be used for other purposes. For example, to perform local fault diagnosis, write a small program and load it into the SRAM to diagnose other
circuits , or use this method to read and write the Flash or EEPROM on the board. This method can also be used to remove the read and write protection of the internal Flash. Of course, when the read and write protection is removed
, the contents of the Flash are automatically cleared to prevent malicious software from copying.
Generally, the BOOT0 and BOOT1 jumpers are both jumped to 0 (ground). Only in the case of ISP download, BOOT0=1, BOOT1=0. After the download is complete, put

Connect the jumper of BOOT0 back to 0, that is, BOOT0=0, BOOT1=0.

Should STM32F103 configure BOOT0 and BOOT1 to be directly grounded or through resistors?
Q: My STM32F103RET6 is down because BOOT0 and BOOT1 are directly grounded. It's very strange. Has anyone encountered this?
A: The hardware design guide of STM32 also recommends that BOOT0 and 1 be connected to resistors and then to ground.
BOOT0 and BOOT1 are grounded through 10k resistors respectively to facilitate serial port downloading. The downloader controls BOOT0 to a high level, and after downloading, BOOT0 is
restored to a low level. STM32 can enter the user program after resetting. Normally, the user program is directly entered when power is turned on. Whether
boot0 is connected to a 10k resistor or directly to ground, it will not cause chip damage.

Note: If the JTAG related pins are used as ordinary IO, downloading will fail (when BOOT0 is at low level). The solution is to download the program once through the serial port and then download it through JLINK, or configure BOOT0 to high level before downloading.