AN4286 datasheet(5/38 Pages) STMICROELECTRONICS

Part #	AN4286

Description	SPI protocol used in the STM32 bootloader

PDF	38 Pages

Scroll/Zoom	100%

Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

Logo

5 / 38 page

SPI Bootloader code sequence

AN4286

5/38

DocID024458 Rev 2

SPI Bootloader code sequence

The STM32 bootloader is an SPI slave.

For all SPI bootloader operations, the NSS pin (chip select) must be tied low. If the NSS pin

is tied high, the communication on the SPI bus will be ignored by the STM32 slave.

Figure 1. Bootloader for STM32 with SPI

Once the system memory boot mode is entered and the STM32 microcontroller has been

configured (for more details, refer to your STM32 system memory boot mode application

note) the bootloader code begins to scan the SPI_MOSI line pin, waiting to detect a

synchronization byte on the bus (0x5A). Once a detection occurs, the SPI bootloader

firmware waits to receive the acknowledge procedure (refer to Figure 2) and then starts to

receive master commands.

AN4286 Datasheet(PDF) 5 Page - STMicroelectronics