RM0351
90/1830 DocID024597 Rev 5
Embedded boot loader
The embedded boot loader is located in the System memory, programmed by ST during
production. Refer to AN2606 STM32 microcontroller system memory boot mode.
2.6.2 Boot configuration for STM32L496xx/4A6xx devices
In the STM32L496xx/4A6xx devices, three different boot modes can be selected through
the BOOT0 pin or the nBOOT0 bit into the FLASH_OPTR register (if the nSWBOOT0 bit is
cleared into the FLASH_OPTR register), and nBOOT1 bit in FLASH_OPTR register, as
shown in the following table.
The values on both BOOT0 pin (coming from the pin or the option bit) and nBOOT1 bit are
latched on the 4th edge of the internal startup clock source after reset release. It is up to the
user to set nBOOT1 and BOOT0 to select the required boot mode.
The BOOT0 pin or user option bit (depending on the nSWBOOT0 bit value in the
FLASH_OPTR register), and nBOOT1 bit are 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 0x0000 0000, then starts code execution from the boot memory at 0x0000 0004.
Depending on the selected boot mode, main Flash memory, system memory or SRAM1 is
accessible as follows:
• Boot from main Flash memory: the main Flash memory is aliased in the boot memory
space (0x0000 0000), but still accessible from its original memory space
(0x0800 0000). In other words, the Flash memory contents can be accessed starting
from address 0x0000 0000 or 0x0800 0000.
• 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 0000).
• Boot from the embedded SRAM1: the SRAM1 is aliased in the boot memory space
(0x0000 0000), but it is still accessible from its original memory space (0x2000 0000).
Table 6. Boot modes
nBOOT1
FLASH_OPTR[23]
nBOOT0
FLASH_OPTR[27]
BOOT0
pin PH3
nSWBOOT0
FLASH_OPTR[26]
Boot Memory Space
Alias
XX01
Main Flash memory is
selected as boot area
X1X0
Main Flash memory is
selected as boot area
0X11
Embedded SRAM1 is
selected as boot area
00X0
Embedded SRAM1 is
selected as boot area
1X11
System memory is
selected as boot area
10X0
System memory is
selected as boot area
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