AT26F004 datasheet(15/38 Pages) ATMEL

15 / 38 page

3588C–DFLASH–04/06

AT26F004

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.

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 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; 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 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 (refer to “Status Register Commands” on page

19 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.

Protect Sector

Table 9-1.

Sector Protection Register Values

Value

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.

SCK

MSB

00110110

410 11

812

29 30

27 28

OPCODE

AAAA

AAA

ADDRESS BITS A23-A0

HIGH-IMPEDANCE

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