256Mb: 3V Embedded Parallel NOR Flash
Device Protection
Blocks with volatile protection and nonvolatile protection can coexist within the memo-
ry array. If the user attempts to program or erase a protected block, the device ignores
the command and returns to read mode.
The block protection status can be read by performing a read electronic signature or by
issuing an AUTO SELECT command (see the Block Protection table).
Refer to the Block Protection Status table and the Software Protection Scheme figure for
details on the block protection scheme. Refer to the Protection Operations section for a
description of the command sets.
Volatile Protection Mode
Volatile protection enables the software application to protect blocks against inadver-
tent change and can be disabled when changes are needed. Volatile protection bits are
unique for each block and can be individually modified. Volatile protection bits control
the protection scheme only for unprotected blocks whose nonvolatile protection bits
are cleared to 1. Issuing a PROGRAM VOLATILE PROTECTION BIT or CLEAR VOLATILE
PROTECTION BIT command sets to 0 or clears to 1 the volatile protection bits and pla-
ces the associated blocks in the protected (0) or unprotected (1) state, respectively. The
volatile protection bit can be set or cleared as often as needed.
When the device is first shipped, or after a power-up or hardware reset, the volatile pro-
tection bits default to 1 (unprotected).
Nonvolatile Protection Mode
A nonvolatile protection bit is assigned to each block. Each of these bits can be set for
protection individually by issuing a PROGRAM NONVOLATILE PROTECTION BIT com-
mand. Also, each device has one global volatile bit called the nonvolatile protection bit
lock bit; it can be set to protect all nonvolatile protection bits at once. This global bit
must be set to 0 only after all nonvolatile protection bits are configured to the desired
settings. When set to 0, the nonvolatile protection bit lock bit prevents changes to the
state of the nonvolatile protection bits. When cleared to 1, the nonvolatile protection
bits can be set and cleared using the PROGRAM NONVOLATILE PROTECTION BIT and
CLEAR ALL NONVOLATILE PROTECTION BITS commands, respectively.
No software command unlocks the nonvolatile protection bit lock bit unless the device
is in password protection mode; in nonvolatile protection mode, the nonvolatile protec-
tion bit lock bit can be cleared only by taking the device through a hardware reset or
power-up.
Nonvolatile protection bits cannot be cleared individually; they must be cleared all at
once using a CLEAR ALL NONVOLATILE PROTECTION BITS command. They will re-
main set through a hardware reset or a power-down/power-up sequence.
If one of the nonvolatile protection bits needs to be cleared (unprotected), additional
steps are required: First, the nonvolatile protection bit lock bit must be cleared to 1, us-
ing either a power-cycle or hardware reset. Then, the nonvolatile protection bits can be
changed to reflect the desired settings. Finally, the nonvolatile protection bit lock bit
must be set to 0 to lock the nonvolatile protection bits. The device now will operate nor-
mally.
To achieve the best protection, the PROGRAM NONVOLATILE PROTECTION LOCK BIT
command should be executed early in the boot code, and the boot code should be pro-
tected by holding VPP/WP# LOW.
PDF: 09005aef84bd3b68
m29w_256mb.pdf - Rev. B 5/13 EN
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