256Mb: 3V Embedded Parallel NOR Flash
Device Protection
Device Protection
Hardware Protection
The VPP/WP# function provides a hardware method of protecting the four outermost
blocks; that is, the two 32-kword blocks at the top and the two 32-KWord blocks at the
bottom of the address space. When VPP/WP# is LOW, PROGRAM and ERASE operations
on the four outermost blocks are ignored to provide protection. When VPP/WP# is
HIGH, the device reverts to the previous protection status for these four outermost
blocks. PROGRAM and ERASE operations can modify the data in these blocks unless the
blocks are protected using block protection.
When VPP/WP# is raised to VPPH, the device automatically enters the unlock bypass
mode, and command execution time is faster. This must never be done from any mode
except read mode; otherwise the device might be left in an indeterminate state.
A 0.1 μF capacitor should be connected between the VPP/WP# pin and the VSS ground
pin to decouple the current surges from the power supply. The PCB track widths must
be sufficient to carry the currents required during unlock bypass program.
When VPP/WP# returns to HIGH or LOW, normal operation resumes. When operations
execute in unlock bypass mode, the device draws IPP from the pin to supply the pro-
gramming circuits. Transitions from HIGH to VPPH and from VPPH to LOW must be
slower than tVHVPP
.
Note: Micron highly recommends driving VPP/WP# HIGH or LOW. If a system needs to
float the VPP/WP# pin, without a pull-up/pull-down resistor and no capacitor, then an
internal pull-up resistor is enabled.
Table 19: VPP/WP# Functions
VPP/WP# Settings
Function
VIL
Four outermost parameter blocks (first two and last two) protected from PROGRAM or
ERASE operations.
VIH
VPPH
Four outermost parameter blocks (first two and last two) unprotected from PROGRAM or
ERASE operations, unless a software activated protection is in place.
Unlock bypass mode supplies current necessary to speed up PROGRAM execution time.
Software Protection
The following software protection modes are available:
• Volatile protection
• Nonvolatile protection
• Password protection
The device is shipped with all blocks unprotected. On first use, the device defaults to
the nonvolatile protection mode but can be activated in either the nonvolatile protec-
tion or password protection mode.
The desired protection mode is activated by setting either the nonvolatile protection
mode lock bit or the password protection mode lock bit of the lock register (see the Lock
Register section). Both bits are one-time-programmable and nonvolatile; therefore, af-
ter the protection mode has been activated, it cannot be changed, and the device is set
PDF: 09005aef84ecabef
m29dw_256g.pdf - Rev. A 10/12 EN
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