MX29LV320AT/B
ner they choose.The customer-lockable version has the
Security on Silicon Sector (Security Sector) Indicator Bit
permanently set to a "0".Thus, the Security Sector Indi-
cator Bit prevents customer-lockable devices from be-
ing used to replace devices that are factory locked.
Write the three-cycle Enter Security Region command
sequence, and then follow the in-system sector group
protect algorithm as shown in Figure 14, except that RE-
SET may be at either VIH or VID. This allows in-system
protection of the without raising any device pin to a high
voltage. Note that this method is only applicable to the
Security Sector.
The system accesses the Security Sector through a
command sequence (see "Enter Security Sector/Exit
Security Sector Command Sequence"). After the sys-
tem has written the Enter Security Sector command se-
quence, it may read the Security Sector by using the ad-
dresses normally occupied by the boot sectors. This
mode of operation continues until the system issues the
Exit Security Sector command sequence, or until power
is removed from the device. On power-up, or following a
hardware reset, the device reverts to sending commands
to the boot sectors.
Write the three-cycle Enter Security Region command
sequence, and then use the alternate method of sector
protection described in the "Sector/Sector Block Protec-
tion and Unprotection section.
Once the Security Sector is locked and verified, the sys-
tem must write the Exit Security Sector Region com-
mand sequence to return to reading and writing the re-
mainder of the array.
The Security Sector protection must be used with cau-
tion since, once protected, there is no procedure avail-
able for unprotecting the Security Sector area and none
of the bits in the Security Sector memory space can be
modified in any way.
Factory Locked: Security Sector Programmed
and Protected at the Factory
In a factory locked device, the Security Sector is pro-
tected when the device is shipped from the factory. The
Security Sector cannot be modified in any way. The de-
vice is available preprogrammed with one of the follow-
ing:
DATA PROTECTION
The MX29LV320AT/B is designed to offer protection
against accidental erasure or programming caused by
spurious system level signals that may exist during power
transition. During power up the device automatically re-
sets the state machine in the Read mode. In addition,
with its control register architecture, alteration of the
memory contents only occurs after successful comple-
tion of specific command sequences. The device also
incorporates several features to prevent inadvertent write
cycles resulting fromVCC power-up and power-down tran-
sition or system noise.
A random, secure ESN only.
Customer code through the Express Flash service.
Both a random, secure ESN and customer code through
the Express Flash service.
In devices that have an ESN, a Bottom Boot device will
have the 16-byte (8-word) ESN in the lowest address-
able memory area starting at 00000h and ending at
0000Fh (00007h). In the Top Boot device the starting
address of the ESN will be at the bottom of the lowest 8
Kbyte (4 Kword) boot sector starting at 3F0000h
(1F8000h) and ending at 3F000Fh (1F8007h).
LOW VCC WRITE INHIBIT
When VCC is less than VLKO the device does not ac-
cept any write cycles. This protects data during VCC
power-up and power-down.The command register and
all internal program/erase circuits are disabled, and the
device resets. Subsequent writes are ignored until VCC
is greater thanVLKO. The system must provide the proper
signals to the control pins to prevent unintentional write
whenVCC is greater thanVLKO.
Customer Lockable: Security Sector NOT Pro-
grammed or Protected at the Factory
If the security feature is not required, the Security Sec-
tor can be treated as an additional Flash memory space,
expanding the size of the available Flash array by 64
Kbytes (32 Kwords). The Security Sector can be read,
programmed, and erased as often as required.The Se-
curity Sector area can be protected using one of the
following procedures:
P/N:PM1008
REV. 1.1, MAY 28, 2004
14
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