AS8267 datasheet(89/136 Pages) AMSCO

89 / 136 page

Data Sheet AS8267 / AS8268

Revision 1.0, 19-Jun-07

Page 89 of 136

SET_PASSWORD

CMD

8 bytes

ACK / NACK

RXD

TXD

In this mode the ATK_EN bit (bit5) is enabled in the Flash status register (9700h), and the attack register logs

any unauthorized access to the device and stores it in the Flash memory. Also in this mode 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. 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.

In case an incorrect password is entered the Attack Counter is increased. After five attacks the UART1 will be

disabled by switching off the internal clock for the UART1.

In this state the device is locked forever.

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

required.

To give the user the possibility of reusing a blocked device he has to implement special functionality in his

software.

The following example describes a possible implementation.

Monitoring of one of the non blocked interfaces (SPI2 or UART2) within the customer specific MCU

software

If a specific (defined by the developer) sequence is applied the MCU can perform a page erase of the

up most page (holds also program length) in the Flash memory.

After a reset the device will now start with its default parameters and will not perform an automatic

program load via the boot loader.

In this operating mode it is than possible to write the program length again into the Flash memory. Also

a new password can be entered.

After a reset the meter will work again and also stored metering data can be accessed.

MCU Access to the FLASH Memory

The listed commands are available for the MCU access.

READ

WRITE Byte

PAGE ERASE

Initiation of a PAGE ERASE by the MCU the CPU_PE bit in the FLASH Status Register (9700h) has to be set.

After this a WRITE command with the selected address has to be performed.

After completion of the page erase procedure the CPU_PE bit has to be cleared by the MCU.

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