256Mb: 3V Embedded Parallel NOR Flash
Device Protection
permanently to operate in the selected protection mode. It is recommended that the
desired software protection mode be activated when first programming the device.
For the four outermost blocks (that is the two blocks at the top and the two at the bot-
tom of the address space), an even higher level of block protection can be achieved by
locking the blocks using the non-volatile protection and then by holding VPP /WP#
LOW.
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 places the associ-
ated blocks in the protected (0) or unprotected (1) state, respectively. The volatile pro-
tection bit can be set or cleared as often as needed. The default values of the volatile
protections are set through the volatile lock boot bit of the lock register (See the Lock
Register section).
When the parts are first shipped, or after a power-up or hardware reset, the volatile pro-
tection bits can be set or cleared depending upon the ordering option chosen: if the op-
tion to clear the volatile protection bits after power-up is selected, then the blocks can
be programmed or erased depending on the nonvolatile protection bits state (See the
Block Protection Status table); If the option to set the volatile protection bits after pow-
er-up is selected, the blocks default to be protected (Refer also to the Protection com-
mands).
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-
PDF: 09005aef84ecabef
m29dw_256g.pdf - Rev. A 10/12 EN
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