DocID017068 Rev 4

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AN3156

Bootloader code sequence

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Figure 2. Bootloader for other STM32 devices

1. After system reset, the device may return to the BL_DFU loop or execute code from Flash memory/RAM

depending on the connection states and the boot pin status.

2. Leave DFU is achieved by a 0 Data Download request followed by GetStatus request and Device Reset.

3. For some products, the external oscillator HSE is not used for USB Bootloader operations and only internal

oscillator HSI is used. Check AN2606 product's section to know which oscillator is required for each

product.

Note:

At Bootloader Startup, the internal oscillator (HSI) is used as clock source for the USB

interface. When USB event is detected, the external oscillator is configured as USB clock

source.