M29DW128F datasheet(83/94 Pages) STMICROELECTRONICS

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M29DW128F

Extended Memory Block

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Appendix C

Extended Memory Block

The M29DW128F has an extra block, the Extended Block, that can be accessed using a

dedicated command.

This Extended Block is 128 Words in x16 mode and 256 bytes in x8 mode. It is used as a

security block (to provide a permanent security identification number) or to store additional

information.

The Extended Block is divided into two memory areas of 64 Words each:

●

The first one is Factory Locked.

●

The second one is Customer Lockable. It is up to the customer to protect it from

program operations. Its status is indicated by bit DQ6 and DQ7. When DQ7 is set to ‘1’

and DQ6 to ‘0’, it indicates that this second memory area is Customer Lockable. When

DQ7 and DQ6 are both set to ‘1’, it indicates that the second part of the Extended Block

is Customer Locked and protected from program operations. Bit DQ7 being

permanently locked to either ‘1’ or ‘0’ is another security feature which ensures that a

customer lockable device cannot be used instead of a factory locked one.

Bits DQ6 and DQ7 are the most significant bits in the Extended Block Protection Indicator

and a specific procedure must be followed to read it. See “Section 3.6.2: Verify Extended

Block Protection Indicator” and Table 5 and Table 8, Block Protection, for details of how to

read bit DQ7.

The Extended Block can only be accessed when the device is in Extended Block mode. For

details of how the Extended Block mode is entered and exited, refer to the Section 6.1.11:

Program command and Section 6.3.2: Exit Extended Block command paragraphs, and to

Table 15 and Table 16, Block Protection Commands.

C.1

Factory Locked Section of the Extended Block

The first section of The Extended Block is permanently protected from program operations

and cannot be unprotected. The Random Number, Electronic Serial Number (ESN) and

Security Identification Number (see Table 41: Extended Block Address and Data) are written

in this section in the factory.

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