M36W832TE Datasheet, PDF (21/64 Pages) STMicroelectronics – 32 Mbit 2Mb x16, Boot Block Flash Memory and 8 Mbit 512Kb x16 SRAM, Multiple Memory Product

M36W832TE, M36W832BE
Flash Block Locking
The Flash Memory features an instant, individual
block locking scheme that allows any block to be
locked or unlocked with no latency. This locking
scheme has three levels of protection.
s Lock/Unlock - this first level allows software-
only control of block locking.
s Lock-Down - this second level requires
hardware interaction before locking can be
changed.
s V_PPF ≤ V_PPLK - the third level offers a complete
hardware protection against program and erase
on all blocks.
The protection status of each block can be set to
Locked, Unlocked, and Lock-Down. Table 10, de-
fines all of the possible protection states (WPF,
DQ1, DQ0), and Appendix C, Figure 32, shows 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. Subsequent reads at the
address specified in Table 6, will output the protec-
tion status of that block. The lock status is repre-
sented by DQ0 and DQ1. DQ0 indicates the Block
Lock/Unlock status and is set by the Lock com-
mand and cleared by the Unlock command. It is
also automatically set when entering Lock-Down.
DQ1 indicates the Lock-Down status 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 after a hardware reset is Locked
(states (0,0,1) or (1,0,1)). Locked blocks are fully
protected from any program or erase. Any pro-
gram or erase operations 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 commands. An Unlocked block can be
Locked by issuing 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 ap-
propriate software commands. A locked block can
be unlocked 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 cannot be changed using soft-
ware 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 pow-
ered-down.
The Lock-Down function is dependent on the WPF
input pin. When WPF=0 (V_IL), the blocks in the
Lock-Down state (0,1,x) are protected from pro-
gram, erase and protection status changes. When
WPF=1 (V_IH) the Lock-Down function is disabled
(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 WPF
remains high. When WPF is low , blocks that were
previously Locked-Down return to the Lock-Down
state (0,1,x) regardless of any changes made
while WPF 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 Appendix D, Com-
mand Interface and Program/Erase Controller
State, for detailed information on which com-
mands are valid during erase suspend.
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