AN4206 datasheet(19/34 Pages) STMICROELECTRONICS

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AN4206

Boot configuration

In the STM32F3xx, three different boot modes can be selected through the BOOT0 pin and

nBOOT1 option bit, as shown in Table 1.

The values on both BOOT0 pin and nBOOT1 bit are latched on the 4th rising edge of

SYSCLK after a reset. The user must set nBOOT1 and BOOT0 to select the required boot

mode.

The BOOT0 pin and nBOOT1 bit are also re-sampled when exiting from Standby mode.

Consequently they must be kept in the required Boot mode configuration in Standby mode.

After the startup delay has elapsed, the CPU fetches the top-of-stack value from address

0x0000 0000, then starts code execution from the boot memory at 0x0000 0004.

Depending on the selected boot mode, main Flash memory, system memory or SRAM is

accessible as follows:



Boot from main Flash memory: the main Flash memory is aliased in the boot memory

space (0x0000 0000), but is still accessible from its original memory space

(0x0800 0000). In other words, the Flash memory contents can be accessed starting

from address 0x0000 0000 or 0x0800 0000.



Boot from System memory: the system memory is aliased in the boot memory space

(0x0000 0000), but is still accessible from its original memory space (0x1FFF EC00).



Boot from embedded SRAM: the SRAM is aliased in the boot memory space (0x0000

0000), but is still accessible from its original memory space (0x2000 0000).

Note:

In the STM32F3 series devices embedding a CCM RAM is not possible to boot from the

CCM SRAM mapped at 0x1000 0000.

The embedded boot loader is located in the System memory, programmed by ST during

production. It is used to reprogram the Flash memory using one of the following interfaces:



USART1(PA9/PA10), USART2(PD5/PD6) or USB(PA11/PA12) on

STM32F302/303xB/C devices,



USART1(PA9/PA10), USART2(PA2/PA3) or USB(PA11/PA12) on STM32F301/302x6/8

and STM32F302/303xD/E devices,



USART1 (PA9/PA10), USART2 (PA2/PA3), I2C1 (PB6/PB7) on STM32F303x6/8 and

STM32F334 devices.



USART1 (PA9/PA10), USART2 (PA2/PA3), I2C1 (PB6/PB7), I2C3 (PA8/PB5) on

STM32F398 and F318 devices.

For additional information, refer to application note AN2606.

Table 1. Boot modes

Boot mode selection

Boot mode

Aliasing

BOOT1(1)

The BOOT1 value is the opposite of the nBOOT1 option bit.

BOOT0

Main Flash memory

Main Flash memory is selected as boot space

System memory

System memory is selected as boot space

Embedded SRAM

Embedded SRAM is selected as boot space

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