M29W640FT datasheet(63/72 Pages) STMICROELECTRONICS

63 / 72 page

M29W640FT, M29W640FB

9 Part Numbering

63/72

Appendix C Extended Memory Block

The M29W640F 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 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 factory 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 3: Bus

Operations, BYTE = VIL and Table 4: 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 Section 4.3.1: Enter

Extended Block command and Section 4.3.2: Exit Extended Block command, and to Table5

and Table 6: Commands, 8-bit mode, BYTE = VIL.

C.1

Factory Locked Extended Block

In devices where the Extended Block is factory locked, the Security Identification Number is

written to the Extended Block address space (see Table 28: Extended Block Address and Data)

in the factory. The DQ7 bit is set to

‘1’ and the Extended Block cannot be unprotected.

C.2

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 protection 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,

Section D.2: In-System Technique and to the corresponding flowcharts, Figure 18 and

Figure 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, Section D.1: Programmer

Technique and to the corresponding flowcharts, Figure 16 and Figure 17, for a detailed

explanation of the technique).

Once the Extended Block is programmed and protected, the Exit Extended Block command

must be issued to exit the Extended Block mode and return the device to Read mode.

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