M29W641DH datasheet(35/42 Pages) STMICROELECTRONICS

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M29W641DH, M29W641DL, M29W641DU

APPENDIX C. EXTENDED MEMORY BLOCK

The M29W641D has an extra block, the Extended

Block, that can be accessed using a dedicated

command.

This Extended Block is 32 KWords. It is used as a

security block (to provide a permanent security

identification number) or to store additional infor-

mation.

The Extended Block is either Factory Locked or

Customer Lockable, its status is indicated by bit

DQ7. This bit is permanently set to either ‘1’ or ‘0’

at the factory and cannot be changed. When set to

‘1’, it indicates that the device is factory locked and

the Extended Block is protected. When set to ‘0’, it

indicates that the device is customer lockable and

the Extended Block is unprotected. 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 facto-

ry locked one.

Bit DQ7 is the most significant bit in the Extended

Block Verify Code and a specific procedure must

be followed to read it. See “Extended Memory

Block Verify Code” in Table 2, Bus Operations, 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 Enter Extended Block Com-

mand and Exit Extended Block Command para-

graphs, and to Table 3, “Commands”.

Factory Locked Extended Block

In devices where the Extended Block is factory

locked, the Security Identification Number is writ-

ten to the Extended Block address space (see Ta-

ble 24, Extended Block Address and Data) in the

factory. The DQ7 bit is set to ‘1’ and the Extended

Block cannot be unprotected.

Customer Lockable Extended Block

A device where the Extended Block is customer

lockable is delivered with the DQ7 bit set to ‘0’ and

the Extended Block unprotected. It is up to the

customer to program and protect the Extended

Block but care must be taken because the protec-

tion of the Extended Block is not reversible.

There are two ways of protecting the Extended

Block:

Issue the Enter Extended Block command to

place the device in Extended Block mode, then

use the In-System Technique (refer to Appendix

D, In-System Technique and to the

corresponding flowcharts, Figures 18 and 19,

for a detailed explanation of the technique).

Issue the Enter Extended Block command to

place the device in Extended Block mode, then

use the Programmer Technique (refer to

Appendix D, Programmer Technique and to the

corresponding flowcharts, Figures 16 and 17,

for a detailed explanation of the technique).

Once the Extended Block is programmed and pro-

tected, the Exit Extended Block command must be

issued to exit the Extended Block mode and return

the device to Read mode.

Table 24. Extended Block Address and Data

Note: 1. See Table 17, Block Addresses.

Device

Address(1)

Data

x16

Factory Locked

Customer Lockable

M29W641D

000000h-000007h

Security Identification Number

Determined by Customer

000008h-007FFFh

Unavailable

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