M28W640FCT STMICROELECTRONICS [STMicroelectronics], M28W640FCT Datasheet - Page 17

• Manufacturer Part Number: M28W640FCT
• Description: 64 Mbit (4Mb x16, Boot Block) 3V Supply Flash Memory
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

BLOCK LOCKING
The M28W640FCT and M28W640FCB feature an
instant, individual block locking scheme that al-
lows any block to be locked or unlocked with no la-
tency. This locking scheme has three levels of
protection.
■
■
■
The protection status of each block can be set to
Locked, Unlocked, and Lock-Down.
fines all of the possible protection states (WP,
DQ1, DQ0), and
a flowchart for the locking operations.
Reading a Block’s Lock Status
The lock status of every block can be read in the
Read Electronic Signature mode of the device. To
enter this mode write 90h to the device. Subse-
quent reads at the address specified in
will output the protection status of that block. The
lock status is represented by DQ0 and DQ1. 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 enter-
ing Lock-Down. DQ1 indicates the Lock-Down sta-
tus and is set by the Lock-Down command. It
cannot be cleared by software, only by a hardware
reset or power-down.
The following sections explain the operation of the
locking system.
Locked State
The default status of all blocks on power-up or af-
ter a hardware reset is Locked (states (0,0,1) or
(1,0,1)). Locked blocks are fully protected from
any program or erase. Any program or erase oper-
ations attempted on a locked block will return an
error in the Status Register. The Status of a
Locked block can be changed to Unlocked or
Lock-Down using the appropriate software com-
mands. An Unlocked block can be Locked by issu-
ing the Lock command.
Unlocked State
Unlocked blocks (states (0,0,0), (1,0,0) (1,1,0)),
can be programmed or erased. All unlocked
blocks return to the Locked state after a hardware
reset or when the device is powered-down. The
status of an unlocked block can be changed to
Locked or Locked-Down using the appropriate
Lock/Unlock - this first level allows software-
only control of block locking.
Lock-Down - this second level requires
hardware interaction before locking can be
changed.
V
hardware protection against program and
erase on all blocks.
PP
V
PPLK
APPENDIX
- the third level offers a complete
C.,
Figure
Table
23., shows
Table
10., de-
6.,
software commands. A locked block can be un-
locked by issuing the Unlock command.
Lock-Down State
Blocks that are Locked-Down (state (0,1,x))are
protected from program and erase operations (as
for Locked blocks) but their protection status can-
not be changed using software commands alone.
A Locked or Unlocked block can be Locked-Down
by issuing the Lock-Down command. Locked-
Down blocks revert to the Locked state when the
device is reset or powered-down.
The Lock-Down function is dependent on the WP
input pin. When WP=0 (V
Lock-Down state (0,1,x) are protected from pro-
gram, erase and protection status changes. When
WP=1 (V
(1,1,1) and Locked-Down blocks can be individu-
ally unlocked to the (1,1,0) state by issuing the
software command, where they can be erased and
programmed. These blocks can then be relocked
(1,1,1) and unlocked (1,1,0) as desired while WP
remains high. When WP is low , blocks that were
previously Locked-Down return to the Lock-Down
state (0,1,x) regardless of any changes made
while WP was high. Device reset or power-down
resets all blocks , including those in Lock-Down, to
the Locked state.
Locking Operations During Erase Suspend
Changes to block lock status can be performed
during an erase suspend by using the standard
locking command sequences to unlock, lock or
lock-down a block. This is useful in the case when
another block needs to be updated while an erase
operation is in progress.
To change block locking during an erase opera-
tion, first write the Erase Suspend command, then
check the status register until it indicates that the
erase operation has been suspended. Next write
the desired Lock command sequence to a block
and the lock status will be changed. After complet-
ing any desired lock, read, or program operations,
resume the erase operation with the Erase Re-
sume command.
If a block is locked or locked-down during an erase
suspend of the same block, the locking status bits
will be changed immediately, but when the erase
is resumed, the erase operation will complete.
Locking operations cannot be performed during a
program suspend. Refer to
mand Interface and Program/Erase Controller
State, for detailed information on which com-
mands are valid during erase suspend.
IH
) the Lock-Down function is disabled
M28W640FCT, M28W640FCB
IL
APPENDIX
), the blocks in the
D., Com-
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