AS8268 datasheet(88/136 Pages) AMSCO

88 / 136 page

Data Sheet AS8267 / AS8268

Revision 1.0, 19-Jun-07

Page 88 of 136

Password Protection

If the protection schema “Protection via PASSWORD” is selected the listed commands are disabled:

READ

WRITE Byte

WRITE Page

PAGE ERASE

MASS ERASE

The password is entered via the SET_PW command (instruction code F7h in the UART1 command interpreter)

followed by the 8byte password.

SET_PASSWORD

CMD

8 bytes

ACK / NACK

RXD

TXD

Once a password is entered it is encrypted and stored in the Flash memory. At the same time the Flash

memory ‘LOCK’ bit (bit6) is set in Flash status register (9700h). When ‘LOCK’ bit is set the top page of the

Flash memory (storage of program length, password, non-volatile status flags) is blocked for page erase and

write access even when access is granted. This also guarantees that the protection remains even the device is

powered down and powered up again.

Based on the blocked write access of the top page of the Flash memory it is not possible to change an existing

password. A new password can only be assigned after a MASS ERASE.

Once the correct password is entered the listed commands are enabled again.

If the device memory is blank (e.g. after FAB-out) the access to the Flash memory is open and no password is

required.

Password + Attack Counter Protection

If the protection schema “Protection via PASSWORD and ATTACK COUNTER” is selected the listed commands

are disabled:

READ

WRITE Byte

WRITE Page

PAGE ERASE

MASS ERASE

The password is entered in this case via the SET_PW1 command (instruction code F8h in the UART1 command

interpreter) followed by the 8byte password.

AS8268 Datasheet(PDF) 88 Page - ams AG