ST AN3155 Application Note

1/37 AN3155 Application note USART protocol used in the STM32™ bootloader Introduction This application note describes the USART protocol used in the STM32 microcontroller bootloader. It details each supported command. For more information about the USART hardware resources and requirements for your device bootloader, please r ...

Contents 1 USART bootloader code sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 2 Choosing the USARTx baud rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1 Minimum baud rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.2 Maximum ...

Doc ID 17066 Rev 2 3/37 List of tables Table 1. USART bootloader commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Table 2. Bootloader protocol versions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 Table 3. Document revision histo ...

AN3155 4/37 Doc ID 17066 Rev 2 List of figures Figure 1. Bootloader for STM32 with USART . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Figure 2. Get command: host side. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Figure 3. Get command: devic ...

Doc ID 17066 Rev 2 5/37 1 USART bootloader code sequence Figure 1. Bootloader for STM32 with USART Once the system memory boot mode is entered and the STM32 microcontroller has been configured (for more details refer to application note AN2606 “STM32 system memory boot mode”) the bootloader code begins to scan the US ...

AN3155 6/37 Doc ID 17066 Rev 2 2 Choosing the USARTx baud rate The calculation of the serial baud rate for USARTx, from the length of the first byte that is received, is used to operate the bootloader within a wide range of baud rates. However, the upper and lower limits have to be kept, in order to ensure proper data transfer. ...

Doc ID 17066 Rev 2 7/37 3 Bootloader command set The supported commands are listed in Table 1 below. Each command is further described in this section. Communication safety All communications from the programming tool (PC) to the device are verified by: 1. checksum: received blocks of data bytes are XORed. A byte containing the ...

AN3155 8/37 Doc ID 17066 Rev 2 Each packet is either accepted (ACK answer) or discarded (NACK answer): ● ACK = 0x79 ● NACK = 0x1F 3.1 Device-dependent bootloader parameters While the USART bootloader protocol’s command set and sequences are the same for all the STM32 devices, some parameters are device-dependent. For a few comman ...

Doc ID 17066 Rev 2 9/37 3.2 Get command The Get command allows you to get the version of the bootloader and the supported commands. When the bootloader receives the Get command, it transmits the bootloader version and the supported command codes to the host, as described in Figure 2. Figure 2. Get command: host side Figure 3. Ge ...

AN3155 10/37 Doc ID 17066 Rev 2 The STM32 sends the bytes as follows: 3.3 Get Version & Read Protection Status command The Get Version & Read Protection Status command is used to get the bootloader version and the read protection status. When the bootloader receives the command, it transmits the information described below (version, re ...