AN2475 datasheet(21/37 Pages) STMICROELECTRONICS

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AN2475

IAP using the ST Flash loader

21/37

The host sends the bytes to the STR91xFA as follows:

●

Byte 1: 0x31

●

Byte 2: 0xCE

●

Wait for ACK

●

Byte 3 to byte 6: start address

●

Byte 3: MSB and byte 6: LSB

●

Byte 7: Checksum: XOR (byte 3, byte 4, byte 5, byte 6)

●

Wait for ACK

●

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)

●

Wait for ACK

3.2.5

Read command

This command allows the host to read the Flash Bank0 locations. When the STR91xFA

receives the Read Memory command, it transmits the ACK byte to the host. After the

transmission of the ACK byte, the STR91xFA waits for an address (4 bytes: byte 1 is the

MSB and byte 4 is LSB of the address) and for a checksum byte. This address is checked: if

the address is valid and checksum is OK, it transmits an ACK byte, otherwise it transmits a

NACK byte and exits from the command. When the address is valid and checksum is

correct, the STR91xFA sends an ACK byte and waits for the information on the number of

bytes to be transmitted (N-1 value) and for its complement (checksum). If the checksum is

correct then it transmits to the user the needed data (N bytes) starting from the received

address, otherwise it sends a NACK before exiting from the command.

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