AN4080 datasheet(20/35 Pages) STMICROELECTRONICS

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Boot configuration

AN4080

20/35

DocID023035 Rev 4

Boot configuration

In the STM32F0xx, three different boot modes can be selected through the BOOT0 pin and

boot configuration bits nBOOT1, BOOT_SEL and nBOOT0 in the User option byte, as

shown in the following table.

The boot mode configuration is latched on the 4th rising edge of SYSCLK after a reset. It is

up to the user to set boot mode configuration related to the required boot mode. The boot

mode configuration is also re-sampled when exiting from Standby mode. Consequently they

must be kept in the required Boot mode configuration in Standby mode. After this startup

delay has elapsed, the CPU fetches the top-of-stack value from address 0x00000000, then

starts code execution from the boot memory at 0x00000004.

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 (0x00000000), but still accessible from its original memory space (0x08000000).

In other words, the Flash memory contents can be accessed starting from address

0x00000000 or 0x08000000.

•

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

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

STM32F03x and STM32F05x devices, 0x1FFF C400 on STM32F04x devices and

0x1FFF C800 on STM32F07x devices).

•

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

(0x0000 0000), but it is still accessible from its original memory space (0x2000 0000).

Empty check

On STM32F04x devices only, internal empty check flag is implemented to allow easy

programming of the virgin devices by the boot loader. This flag is used when BOOT0 pin is

defining Main Flash memory as the target boot space. When the flag is set, the device is

considered as empty and System memory (boot loader) is selected instead of the Main

Flash as a boot space to allow user to program the Flash memory.

Table 3. Boot modes(1)

1. Grey options are available on STM32F04x devices only.

Boot mode configuration

Mode

n BOOT1

bit

BOOT0

BOOT_SEL

bit

nBOOT0

bit

Main Flash memory is selected as boot

space(2)

2. For STM32F04x devices, see also Empty check description.

System memory is selected as boot space

Embedded SRAM is selected as boot space

Main Flash memory is selected as boot space

System memory is selected as boot space

Embedded SRAM is selected as boot space

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