FW912 Micron Semiconductor Products, FW912 Datasheet - Page 32

• Manufacturer Part Number: FW912
• Description: Flash Memory Technology
• Manufacturer: Micron Semiconductor Products

WAIT# SIGNAL IN BURST MODE
word burst mode with no wrap (RCR3 = 1), the output
WAIT# informs the system when data is valid. When
WAIT# is asserted during delay (RCR8 = 0), WAIT# = 1
indicates valid data and WAIT# = 0 indicates invalid
data. If RCR8 = 0, WAIT# is asserted on the same cycle
on which the delay occurs. If RCR8 = 1, WAIT# is as-
serted one cycle before the delay occurs.
BLOCK LOCKING
that allows each block to be individually locked or un-
locked with no latency.
The first level allows software-only control of block lock-
ing (for data that needs to be changed frequently),
while the second level requires hardware interaction
before locking can be changed (code which does not
require frequent updates).
of a block; for example, state [001] means WP# = 0, DQ1
= 0 and DQ0 = 1.
NOTE: All blocks are software-locked upon comple-
LOCKED STATE
reset sequence, all blocks are locked (states [001] or
[101]). This means full protection from alteration. Any
PROGRAM or ERASE operations attempted on a locked
block will return an error on bit SR1 of the status regis-
ter. The status of a locked block can be changed to
unlocked or lock down using the appropriate software
commands. Writing the lock command sequence, 60h
followed by 01h, can lock an unlocked block.
UNLOCKED STATE
programmed or erased. All unlocked blocks return to
the locked state when the device is reset or powered
down. An unlocked block can be locked or locked down
using the appropriate software command sequence,
60h followed by D0h (see Table 4).
LOCKED DOWN STATE
tected from PROGRAM and ERASE operations, but their
protection status cannot be changed using software
commands alone. A locked or unlocked block can be
locked down by writing the lock down command se-
quence, 60h followed by 2Fh. Locked down blocks re-
4 Meg x 16 Async/Page/Burst Flash Memory
MT28F642D18_3.p65 – Rev. 3, Pub. 8/02
In the continuous burst mode or in the four- or eight-
The Flash devices provide a flexible locking scheme
The devices offer two-level protection for the blocks.
Control signals WP#, DQ1, and DQ0 define the state
Table 12 defines all of the possible locking states.
After a power-up sequence completion, or after a
Unlocked blocks (states [000], [100], [110]) can be
Blocks that are locked down (state [011]) are pro-
tion of a power-up sequence.
ASYNC/PAGE/BURST FLASH MEMORY
32
vert to the locked state when the device is reset or
powered down.
input. When WP# = 0, blocks in lock down [011] are
protected from program, erase, and lock status
changes. When WP# = 1, the lock down function is dis-
abled ([111]), and locked down blocks can be individu-
ally unlocked by a software command to the [110] state,
where they can be erased and programmed. These
blocks can then be relocked [111] and unlocked [110]
as desired while WP# remains HIGH. When WP# goes
LOW, blocks that were previously locked down return
to the locked down state [011] regardless of any
changes made while WP# was HIGH. Device reset or
power-down resets all locks, including those in lock
down, to locked state (see Table 13).
READING A BLOCK’S LOCK STATUS
read device identification mode. To enter this mode,
write 90h to the device. Subsequent READs at block
address +00002 will output the lock status of that block.
The lowest two outputs, DQ0 and DQ1, represent the
lock status. DQ0 indicates the block lock/unlock status
and is set by the LOCK command and cleared by the
UNLOCK command. It is also automatically set when
entering lock down. DQ1 indicates lock down status
and is set by the LOCK DOWN command. It can only be
cleared by reset or power-down, not by software. Table
12 shows the locking state transition scheme.
LOCKING OPERATIONS DURING ERASE
SUSPEND
ing an ERASE SUSPEND by using the standard locking
command sequences to unlock, lock, or lock down. This
is useful in the case when another block needs to be
updated while an ERASE operation is in progress.
tion, first write the ERASE SUSPEND command (B0h),
then check the status register until it indicates that the
ERASE operation has been suspended. Next, write the
desired lock command sequence to block lock, and the
lock status will be changed. After completing any de-
sired LOCK, READ, or PROGRAM operation, resume
the ERASE operation with the ERASE RESUME com-
mand (D0h).
ERASE SUSPEND operation on the same block, the
locking status bits will be changed immediately. Then,
when the ERASE is resumed, the ERASE operation will
complete.
PROGRAM SUSPEND.
The LOCK DOWN function is dependent on the WP#
The lock status of every block can be read in the
Changes to block lock status can be performed dur-
To change block locking during an ERASE opera-
If a block is locked or locked down during an
A locking operation cannot be performed during a
Micron Technology, Inc., reserves the right to change products or specifications without notice.
4 MEG x 16
©2002, Micron Technology, Inc.
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