m29dw256g Numonyx, m29dw256g Datasheet - Page 79

• Manufacturer Part Number: m29dw256g
• Description: 256-mbit X16, Multiple Bank, Page, Dual Boot 3 V Supply Flash Memory
• Manufacturer: Numonyx

Appendix C
C.1
The M29DW256G has an extra block, the extended memory block, that can be accessed
using a dedicated command. This extended memory block is 128 words. 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.
The extended memory block cannot be erased, and is one-time programmable (OTP)
memory. If memory block is factory locked or customer protected by setting the extended
memory block protection bit, it cannot be further modified.
If the extended memory block is not factory locked, it can be customer lockable. Its status is
indicated by bit DQ7 in autoselect mode. 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 or the in-system method.
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
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
memory block address and
memory block cannot be unprotected.
Section 6.4.2: Extended Memory
Extended memory block
data) in the factory. The DQ7 bit is set to ‘1’ and the extended
Block.
Table 41: Extended
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