M29W640FB STMICROELECTRONICS [STMicroelectronics], M29W640FB Datasheet - Page 63

• Manufacturer Part Number: M29W640FB
• Description: 64 Mbit (8Mb x8 or 4Mb x16, Page, Boot Block) 3V Supply Flash Memory
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

M29W640FT, M29W640FB
Appendix C Extended Memory Block
C.1
C.2
Factory Locked Extended Block
Customer Lockable Extended 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
Operations, BYTE = VIL
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
Extended Block command
and
In devices where the Extended Block is factory locked, the Security Identification Number is
written to the Extended Block address space (see
in the factory. The DQ7 bit is set to ‘1’ and the Extended Block cannot be unprotected.
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:
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.
Table 6: Commands, 8-bit mode, BYTE =
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
Section D.2: In-System Technique
Figure
Issue the Enter Extended Block command to place the device in Extended Block mode,
then use the Programmer Technique (refer to
Technique
explanation of the technique).
19, for a detailed explanation of the technique).
and to the corresponding flowcharts,
and
and
Table 4: Bus Operations, BYTE =
Section 4.3.2: Exit Extended Block
and to the corresponding flowcharts,
VIL.
Table 28: Extended Block Address and
Appendix
Figure 16
IH
D,
or at V
VIH, for details of how to read bit
and
Section D.1: Programmer
command, and to
ID
Figure
” in
(refer to
Table 3: Bus
Section 4.3.1: Enter
17, for a detailed
Figure 18
Appendix
9 Part Numbering
Table 5
and
D,
Data)
63/72