Here is a detailed description of the STM32 microcontroller serial port one-button download circuit and operation method. The storage media corresponding to the three boot modes of STM32 are all built into the chip. They are: 1) User flash = Flash built into the chip. 2) SRAM = The RAM area built into the chip is the memory. 3) System Memory = A specific area inside the chip. When the chip leaves the factory, a Bootloader is preset in this area, which is usually called ISP program. The content of this area is not modified or erased after the chip is shipped, ie it is a ROM area. To understand the several startup modes of STM32. BOOT0 is connected to GND, BOOT1 is connected to GND. That is the normal startup mode, loading code from flash. BOOT0 is connected to V3.3, BOOT1 is connected to GND. It is ISP mode, which is the serial port update code. Second, you need to understand the process of downloading code from STM32 ISP. First BOOT0 is connected to V3.3, then reset STM32.STM32 will load the ISP code (cure stored in the internal), thus entering the ISP mode. At this point you can download the program through the serial port. Finally, let's see how one-click download is implemented. From the schematic diagram, the RTS control BOOT0 of the DB9 serial port and the DTR control RST. To achieve the purpose of downloading, we must first let RTS pull BOOT0 (set BOOT0 to 1), then let DTR control RST low (STM32 is low reset), then release RTS high (stop reset), Then start the serial port download code (at this time BOOT0 can be high or low). So we see that the mcuisp connection process is: DTR level is set high (3-12V), reset (DTR is connected to RST) RTS is set low (-3--12V), choose to enter BootLoader (RTS is connected to BOOT0) ...delay 100 milliseconds RTS level goes high (+3-+12V) release reset (release reset, but BOOT0 is high at this time, so enter ISP mode) Start connecting...4, received: 1F (connection successful) The serial port COM0 connection succeeded @230400bps, which took 437 milliseconds DTR remains high [Note that DTR_N is the inverting level of DTR. RTS_N is the inverting level of RTS] Note: This circuit does not require a USB to serial port chip, as long as an ordinary DB9 serial port can complete the program download work. For those microcontroller-only boards with serial ports, this is a perfect choice.
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