Boot Mode Selection; Table 5. Boot Modes For Stm32L4 Cat. 2 Devices And Stm32L1 Lines; Table 6. Boot Modes For Stm32L4 Cat. 4 Devices - ST STM32L1 Series Application Note

Boot mode selection

3 Boot mode selection
Both STM32L1 and STM32L4 Series can select boot modes between three options: boot
from main Flash memory, boot from SRAM or boot from system memory.
However, the way to select the boot mode differs between the products.
In the STM32L1 lines, the boot mode is selected with two pins BOOT0 and BOOT1.
In the STM32L4 Cat. 2 devices, the boot mode is selected with 1 pin BOOT0 and the
nBOOT1 option bit located in the user option bytes at memory address 0x1FFF7800.
In the STM32L4 Cat. 4 devices, the boot mode is selected with nBOOT1 option bit and pin
BOOT0 or nBOOT0 option bit depending on the value of the nSWBOOT0 option bit in the
FLASH_OPTR register as shown in table below.
Table 5 and
mode.
BOOT1
1. The BOOT1 value is the opposite of the nBOOT1 option bit.
nBOOT1
FLASH_OPTR
[23]
x
x
x
14/58
Table 6 summarizes the different configurations available for selecting the boot

Table 5. Boot modes for STM32L4 Cat. 2 devices and STM32L1 lines

L4/L1 boot mode selection
(1)
x
0
1

Table 6. Boot modes for STM32L4 Cat. 4 devices

nBOOT0
FLASH_OPTR
[27]
x
x
1
DocID027094 Rev 3
Boot mode
BOOT0
0 Main Flash memory
1 System memory
1 Embedded SRAM
nSWBOOT0
BOOT0 pin
FLASH_OPTR
PH3
[26]
0
0
x
Main Flash memory is
selected as boot space
System memory is
selected as boot space
Embedded SRAM is
selected as boot space
Main Flash
(1)
empty
1 0
1 1
0 x
AN4612
Aliasing
Boot Memory
Space Alias
Main Flash
memory is
selected as
boot area
System
memory is
selected as
boot area
Main Flash
memory is
selected as
boot area