AT25DF081A datasheet(20/54 Pages) ETC2

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8715C–SFLSH–1/2013

AT25DF081A

9.4

Unprotect Sector

Issuing the Unprotect Sector command to a particular sector address will reset the corresponding Sector Protec-

tion Register to the logical “0” state (see Table 9-1 for Sector Protection Register values). 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.

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 designating 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 deas-

serted, 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 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 deasserted, and the CS pin

must be deasserted on an even byte boundary (multiples of eight bits); otherwise, the device will abort the 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 locking or unlocking of sectors, the Sector Protection Registers

can themselves be locked from updates by using the SPRL (Sector Protection Registers Locked) bit of the Status

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.

Unprotect Sector

SCK

MSB

00111001

410 11

812

29 30

27 28

OPCODE

AAAA

AAA

ADDRESS BITS A23-A0

HIGH-IMPEDANCE

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