Boot configuration

AN3320

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Doc ID 18267 Rev 2

3

Boot configuration

3.1

Boot mode selection

In the STM32F20xxx/21xxx, three different boot modes can be selected by means of the

BOOT[1:0] pins as shown in Table 1.

is up to the user to set the BOOT1 and BOOT0 pins after reset to select the required boot

mode.

The BOOT pins are also resampled when exiting the Standby mode. Consequently, they

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

delay has elapsed, the CPU fetches the top-of-stack value from address 0x0000 0000, and

starts code execution from the boot memory starting from 0x0000 0004.

3.2

Boot pin connection

Figure 10 shows the external connection required to select the boot memory of the

STM32F20xxx/21xxx.

Figure 10.

Boot mode selection implementation example

1.

Resistor values are given only as a typical example.

Table 1.

Boot modes

BOOT mode selection pins

Boot mode

Aliasing

BOOT1

BOOT0

x

0

Main Flash memory

Main Flash memory is selected as boot

space

0

1

System memory

System memory is selected as boot

space

1

1

Embedded SRAM

Embedded SRAM is selected as boot

space

Ω

Ω