AT26F004-SSU ATMEL [ATMEL Corporation], AT26F004-SSU Datasheet - Page 16

• Manufacturer Part Number: AT26F004-SSU
• Description: 4-megabit 2.7-volt Only Serial Firmware DataFlash Memory
• Manufacturer: ATMEL [ATMEL Corporation]

9.4
16
Unprotect Sector
AT26F004
Issuing the Unprotect Sector command to a particular sector address will reset the correspond-
ing Sector Protection Register to the logical “0” state (see
Register values). Every physical sector of the device has a corresponding single-bit Sector Pro-
tection Register that is used to control the software protection of a sector.
Before the Unprotect 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
Unprotect Sector command, the CS pin must first be asserted and the opcode of 39h must be
clocked into the device. After the opcode has been clocked in, the three address bytes designat-
ing any address within the sector to be unlocked must be clocked in. Any additional data clocked
into the device after the address bytes will be ignored. When the CS pin is deasserted, the Sec-
tor Protection Register corresponding to the sector addressed by A23 - A0 will be reset to the
logical “0” state, and the sector itself will be unprotected. In addition, the WEL bit in the Status
Register will be reset back to the logical “0” state.
The complete three address bytes must be clocked into the device before the CS pin is deas-
serted; otherwise, the device will abort the operation, the state of the Sector Protection Register
will be unchanged, and the WEL bit in the Status Register will be reset to a logical “0”.
As a safeguard against accidental or erroneous locking or unlocking of sectors, the Sector Pro-
tection Registers can themselves be locked from updates by using the SPRL (Sector Protection
Registers Locked) bit of the Status Register (refer to
for more details). If the Sector Protection Registers are locked, then any attempts to issue the
Unprotect Sector command will be ignored, and the device will reset the WEL bit in the Status
Register back to a logical “0” and return to the idle state once the CS pin has been deasserted.
Figure 9-4.
SCK
CS
SO
SI
Unprotect Sector
MSB
HIGH-IMPEDANCE
0
0
0
1
1
2
OPCODE
1
3
1
4
0
5
0
6
1
7
MSB
A
8
A
9
A
10 11
A
ADDRESS BITS A23-A0
“Status Register Commands” on page 19
A
12
A
Table 9-1
A
26
A
27 28
A
A
29 30
for Sector Protection
A
A
31
3588A–DFLSH–10/05