M29W640GH, M29W640GL, M29W640GT, M29W640GB
Extended Memory Block
Appendix C Extended Memory Block
The M29W640G 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 7:
Bus Operations, BYTE = V and Table 8: Bus Operations, BYTE = V , for details of how to
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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
Table 10 and Table 11: Commands, 8-bit mode, BYTE = V .
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C.1
C.2
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 36: 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 protection of the Extended Block is not
reversible.
There are two ways of protecting the Extended Block:
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Issue the Enter Extended Block command to place the device in Extended Block mode,
then use the In-System Technique with RP either at V or at V (refer to Section D.2:
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In-System Technique and to the corresponding flowcharts, Figure 27 and Figure 28, 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, Section D.1: Programmer Technique and
to the corresponding flowcharts, Figure 25 and Figure 26, 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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