M29W640DB datasheet(42/49 Pages) STMICROELECTRONICS

42 / 49 page

M29W640DT, M29W640DB

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APPENDIX C. EXTENDED MEMORY BLOCK

The M29W640D has an extra block, the Extended

Block, that can be accessed using a dedicated

command.

This Extended Block is 32 KWords in x16 mode

and 64 KBytes in x8 mode. It is used as a security

block (to provide a permanent security identifica-

tion number) or to store additional information.

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,

BYTE = VIL and Table 3., Bus Operations, BYTE =

VIH, 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 4., Commands, 16-bit mode,

BYTE = VIH and Table 5., Commands, 8-bit mode,

BYTE = VIL.

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 27., 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 with RP

either at VIH or at VID (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 27. Extended Block Address and Data

Note: 1. See Tables 19 and 20, Top and Bottom Boot Block Addresses.

Device

Address(1)

Data

x16

Factory Locked

Customer Lockable

M29W640DT

7F0000h-7F000Fh

3F8000h-3F8007h

Security Identification

Number

Determined by

Customer

7F0010h-7FFFFFh

3F8008h-3FFFFFh

Unavailable

M29W640DB

000000h-00000Fh

000000h-000007h

Security Identification

Number

Determined by

Customer

000010h-00FFFFh

000008h-007FFFh

Unavailable

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