M29W128GH, M29W128GL
Extended memory block
Appendix C
Extended memory block
The M29W128GH/L has an extra block, the extended memory block, that can be accessed
using a dedicated command. This extended memory block is 128 words in x 16 mode and
256 bytes in x 8 mode. It is used as a security block (to provide a permanent security
identification number) or to store additional information.
The device can be shipped either with the extended memory block factory locked, or factory
unlocked.
If the extended memory block is not factory locked, it can be 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
memory block is protected. When set to ‘0’, it indicates that the device is customer lockable.
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 Memory Block Verify Indicator. It can be
read in Auto Select mode using either the Programmer (see Table 8 and Table 9) or the In-
system method (see Table 10 and Table 11).
The extended memory block can only be accessed when the device is in Extended Memory
Block mode. For details of how the Extended Memory Block mode is entered and exited,
refer to the Section 6.3.1: Enter Extended Memory Block command and Section 6.3.2: Exit
Extended Memory Block command, and to Table 15 and Table 10.
C.1
Factory locked extended memory block
In devices where the extended memory block is factory locked, the security identification
number is written to the extended memory block address space (see Table 41: Extended
memory block address and data) in the factory. The DQ7 bit is set to ‘1’ and the extended
memory block cannot be unprotected.
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