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9.2
Write Disable
The Write Disable command is used to reset the Write Enable Latch (WEL) bit in the Status Reg-
ister to the logical “0” state. With the WEL bit reset, all program, erase, Protect Sector, Unprotect
Sector, and Write Status Register commands will not be executed. The Write Disable command
is also used to exit the Sequential Program Mode. Other conditions can also cause the WEL bit
to be reset; for more details, refer to the WEL bit section of the Status Register description.
To issue the Write Disable command, the CS pin must first be asserted and the opcode of 04h
must be clocked into the device. No address bytes need to be clocked into the device, and any
data clocked in after the opcode will be ignored. When the CS pin is deasserted, the WEL bit in
the Status Register will be reset to a logical “0”. The complete opcode must be clocked into the
device before the CS pin is deasserted, and the CS pin must be deasserted on an even byte
boundary (multiples of eight bits); otherwise, the device will abort the operation and the state of
the WEL bit will not change.
Figure 9-2.
Write Disable
C S
0
1
2
3
4
5
6
7
S CK
OPCODE
S I
0
0
0
0
0
1
0
0
M S B
S O
HIGH-IMPEDANCE
9.3
Protect Sector
Every physical sector of the device has a corresponding single-bit Sector Protection Register
that is used to control the software protection of a sector. Upon device power-up or after a
device reset, each Sector Protection Register will default to the logical “1” state indicating that all
sectors are protected and cannot be programmed or erased.
Issuing the Protect Sector command to a particular sector address will set the corresponding
Sector Protection Register to the logical “1” state. The following table outlines the two states of
the Sector Protection Registers.
Table 9-1.
Value
0
1
Sector Protection Register Values
Sector Protection Status
Sector is unprotected and can be programmed and erased.
Sector is protected and cannot be programmed or erased. This is the default state.
Before the Protect Sector command can be issued, the Write Enable command must have been
previously issued to set the WEL bit in the Status Register to a logical “1”. To issue the Protect
Sector command, the CS pin must first be asserted and the opcode of 36h must be clocked into
the device followed by three address bytes designating any address within the sector to be
locked. Any additional data clocked into the device will be ignored. When the CS pin is deas-
serted, the Sector Protection Register corresponding to the physical sector addressed by
A23 - A0 will be set to the logical “1” state, and the sector itself will then be protected from
16
AT26DF081A
3600G–DFLASH–06/09
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