AN4286 datasheet(21/38 Pages) STMICROELECTRONICS

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Bootloader command set

AN4286

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DocID024458 Rev 2

At the end of the command, if the write operation is successful, the bootloader transmits the

ACK byte; otherwise it transmits a NACK byte to the application and aborts the command.

If the Write Memory command is issued to the Option byte area, all options are erased

before writing the new values, and at the end of the command the bootloader generates a

system reset to take into account the new configuration of the option byte. The start address

and the maximum length of the block to be written in the Option byte area has to respect the

address and size of the product’s option bytes.

If the write memory destination is the Flash Memory then the Master has to wait enough

time for the sent buffer to be written (refer to product datasheet for timing values) before

polling for a slave response.

Note:

The maximum length of the block to be written in the RAM or Flash memory is 256 bytes.

Write operations to the Flash memory must be word (16-bit) aligned and data should be in

multiples of two bytes. If less data is written, the remaining bytes should be filled by 0xFF.

When writing to the RAM, you should take care not to overlap the first RAM memory used

by the bootloader firmware.

No error is returned when performing write operations in write-protected sectors.

The master sends the bytes to the STM32 as follows.

•

Start Of Frame: 0x5A

•

Byte 1: 0x31

•

Byte 2: 0xCE

•

Wait for ACK (as described in Chapter 1):

•

Byte 3 to byte 6: start address

–

byte 3: MSB

–

byte 6: LSB

•

Byte 7: checksum: XOR (Byte3, Byte4, Byte5, Byte6)

•

Wait for ACK (as described in Chapter 1)

•

Byte 8: number of bytes to be received (0 < N ≤ 255)

•

N +1 data bytes: (max 256 bytes)

•

Checksum byte: XOR (N, N+1 data bytes)

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