AT25DF321A datasheet(20/51 Pages) RENESAS

20 / 51 page

3686I–DFLASH–02/2019

AT25DF321A

Figure 9-3. Protect Sector

9.4

Unprotect Sector

Issuing the Unprotect Sector command to a particular sector address will reset the corresponding Sector Protection 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 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 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 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 Protection Registers can themselves

be locked from updates by using the SPRL (Sector Protection 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

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

10 11

29 30

27 28

OPCODE

ADDRESS BITS A23-A0

HIGH-IMPEDANCE

SCK