Boot configuration

AN3216

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DocID17496 Rev 7

4

Boot configuration

4.1

Boot mode selection

In the STM32L1xxx, three different boot modes can be selected by means of the BOOT[1:0]

pins as shown in Table 2.

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

mode.

BOOT0 is a dedicated pin while BOOT1 is shared with a GPIO pin. Once BOOT1 has been

sampled, the corresponding GPIO pin is free and can be used by the application.

The BOOT pins are also resampled when exiting 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 0x0000 0000, and starts

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

4.2

Boot pin connection

Figure 12 shows the external connection required to select the boot memory of the

STM32L1xxx.

Figure 12. Boot mode selection implementation example

1. Resistor values are given only as a typical example.

Table 2. 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

ai14373b

STM32L1xxx

BOOT0

BOOT1

10 k

10 k