HY29F400 Datasheet, PDF (9/40 Pages) Hynix Semiconductor – 4 Megabit (512Kx8/256Kx16) 5 Volt-only Flash Memory

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_ID. While in this mode, formerly protected sec-
tors can be programmed or erased by invoking
the appropriate commands (see Device Com-
mands section). Once V_ID is removed from RE-
SET#, all the previously protected sectors are pro-
tected again. Figure 3 illustrates the algorithm.
HY29F400
START
RESET# = V_ID
(All protected sector groups
become unprotected)
Perform Program or Erase
Operations
RESET# = V_IH
(All previously protected
sector groups return to
protected state)
TEMPORARY SECTOR
UNPROTECT COMPLETE
Figure 3. Temporary Sector Unprotect
START
NOTE: All sectors must be
previously protected.
APPLY V _CC
Set: TRYCNT = 1
Set: NSEC = 0
Set: A[9] = CE# = OE# = V _ID
Set: RESET# = V _IH
WE# = V _IL
Wait t_WPP2
WE# = V _IH
Set:
A[9] = V _ID
OE# = CE# = V _IL
Rev. 5.2/May 01
Set Sector Address:
A[17:12] = Sector NSEC
A[0] = A[6] = V _IL
A[1] = V _IH
Read Data
NO
Data = 0x00?
Increment TRYCNT
NO
YES
TRYCNT = 1000?
YES
YES
NSEC = 10?
NO
NSEC = NSEC + 1
Remove V _ID from A[9]
SECTOR UNPROTECT
COMPLETE
DEVICE FAILURE
Figure 2. Sector Unprotect Procedure
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