AN2606 datasheet(67/155 Pages) STMICROELECTRONICS

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AN2606

STM32F302xB(C)/303xB(C) devices bootloader

154

The bootloader has two case of operation depending on the presence of the external clock

(HSE) at bootloader startup:

•

If HSE is present and has a value of 24, 18, 16, 12, 9, 8, 6, 4 or 3 MHz, the system

clock is configured to 48 MHz with HSE as clock source. The DFU interface, USART1

and USART2 are functional and can be used to communicate with the bootloader

device.

•

If HSE is not present, the HSI is kept as default clock source and only USART1 and

USART2 are functional.

The external clock (HSE) must be kept if it’s connected at bootloader startup because it will

be used as system clock source.

USART2 bootloader

USART2

Enabled

Once initialized, the USART2 configuration

is: 8 bits, even parity and 1 Stop bit. The

USART2 uses its remapped pins.

USART2_RX pin

Input

PD6 pin: USART2 in reception mode

USART2_TX pin

Output

PD5 pin: USART2 in transmission mode

DFU bootloader

USB

Enabled

USB used in FS mode

USB_DM pin

Input/Output

PA11: USB DM line.

USB_DP pin

PA12: USB DP line

An external pull-up resistor 1.5 KOhm must

be connected to USB_DP pin.

Table 32. STM32F302xB(C)/303xB(C) configuration in System memory boot mode (continued)

Bootloader

Feature/Peripheral

State

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