at25df641 ATMEL Corporation, at25df641 Datasheet - Page 23

• Manufacturer Part Number: at25df641
• Description: At25df641 64-megabit 2.7-volt Minimum Spi Serial Flash Memory
• Manufacturer: ATMEL Corporation

9.4
3680B–DFLASH–2/08
Unprotect Sector
A23-A0 will be set to the logical “1” state, and the sector itself will then be protected from pro-
gram and erase operations. 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, and the CS pin must be deasserted on an even byte boundary (multiples of eight bits);
otherwise, the device will abort the operation. When the device aborts the Protect Sector opera-
tion, 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 protecting or unprotecting of sectors, the Sector
Protection Registers can themselves be locked from updates by using the SPRL (Sector Protec-
tion Registers Locked) bit of the Status Register (please refer to the Status Register description
for more details). If the Sector Protection Registers are locked, then any attempts to issue the
Protect Sector command will be ignored, and the device will reset the WEL bit in the Status Reg-
ister back to a logical “0” and return to the idle state once the CS pin has been deasserted.
Figure 9-3.
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 unprotected 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 Sector 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 Sta-
tus 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, and the CS pin must be deasserted on an even byte boundary (multiples of eight bits);
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”.
SCK
SO
CS
SI
Protect Sector
HIGH-IMPEDANCE
MSB
0
0
0
1
1
2
OPCODE
1
3
0
4
1
5
1
6
0
7
MSB
A
8
A
AT25DF641 [Preliminary]
9
A
10 11
A
ADDRESS BITS A23-A0
A
12
A
Table 9-1
A
26
A
27 28
A
A
29 30
for Sector Protection
A
A
31
23