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AN4654

Boot mode compatibility

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Boot mode compatibility

The way to select the boot mode on the STM32L0xx products differs from STM32L1xx

product family. Instead of using two pins for the boot mode setting, STM32L0xx products

use BOOT0 pin and retrieve the nBOOT1 value from an option bit located in the User option

bytes at 0x1FF80000 memory address.

On the STM32L01x and STM32L02x devices the BOOT0 pin can be replaced by nBOOT0

bit using the BOOT_SEL bit in the User option bytes. This provides the ability to use the

BOOT0 pin as GPIO input only pin on the device.

Table 3 summarizes the different configurations available for the Boot mode selection.

Note:

The BOOTx value is the opposite of the nBOOTx option bit, where x stands for 1 and 2.

1. Gray options are available on STM32L01x and STM32L02x devices only.

Boot mode configuration

Mode

n BOOT1

bit

BOOT0

pin

BOOT_SEL

bit

nBOOT0

bit

x0

0

x

Main Flash memory is selected as boot space

1

1

0

x

System memory is selected as boot space

0

1

0

x

Embedded SRAM is selected as boot space

x

x

1

1

Main Flash memory is selected as boot space

1

x

1

0

System memory is selected as boot space

0

x

1

0

Embedded SRAM is selected as boot space