HY29F400 Hynix Semiconductor, HY29F400 Datasheet - Page 9

• Manufacturer Part Number: HY29F400
• Description: 4 Megabit (512Kx8/256Kx16) 5 Volt-only Flash Memory
• Manufacturer: Hynix Semiconductor

The procedure for sector unprotection is illustrated
in the flow chart in Figure 2, and timing specifica-
tions and waveforms are given at the end of this
document. Note that to unprotect any sector, all
unprotected sectors must first be protected prior
to the first unprotect write cycle.
Sectors can also be temporarily unprotected as
described in the next section.
Temporary Sector Unprotect Operation
This feature allows temporary unprotection of pre-
viously protected sectors to allow changing the
data in-system. Temporary Sector Unprotect
mode is activated by setting the RESET# pin to
V
tors can be programmed or erased by invoking
the appropriate commands (see Device Com-
mands section). Once V
SET#, all the previously protected sectors are pro-
tected again. Figure 3 illustrates the algorithm.
Rev. 5.2/May 01
ID
. While in this mode, formerly protected sec-
Set: A[9] = CE# = OE# = V
NOTE: All sectors must be
previously protected.
Set: RESET# = V
Set: TRYCNT = 1
OE# = CE# = V
Set: NSEC = 0
APPLY V
W E # = V
W E # = V
Wait t
A[9] = V
START
Set:
W P P 2
ID
CC
IL
IH
IL
IH
ID
ID
is removed from RE-
Figure 2. Sector Unprotect Procedure
A[17:12] = Sector NSEC
Set Sector Address:
NSEC = NSEC + 1
A[0] = A[6] = V
Data = 0x00?
NSEC = 10?
Read Data
A[1] = V
Y E S
N O
IH
IL
N O
Y E S
Figure 3. Temporary Sector Unprotect
SECTOR UNPROTECT
Remove V
Increment TRYCNT
TRYCNT = 1000?
C O M P L E T E
ID
N O
from A[9]
(All protected sector groups
UNPROTECT COMPLETE
Perform Program or Erase
TEMPORARY SECTOR
(All previously protected
sector groups return to
become unprotected)
protected state)
R E S E T # = V
R E S E T # = V
Operations
Y E S
START
ID
IH
DEVICE FAILURE
HY29F400
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