AT25DF081A datasheet(24/54 Pages) ETC2

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8715C–SFLSH–1/2013

AT25DF081A

9.7

Protected States and the Write Protect (WP) Pin

The WP pin is not linked to the memory array itself and has no direct effect on the protection status or lockdown

status of the memory array. Instead, the WP pin, in conjunction with the SPRL (Sector Protection Registers

Locked) bit in the Status Register, is used to control the hardware locking mechanism of the device. For hardware

locking to be active, two conditions must be met-the WP pin must be asserted and the SPRL bit must be in the log-

ical “1” state.

When hardware locking is active, the Sector Protection Registers are locked and the SPRL bit itself is also locked.

Therefore, sectors that are protected will be locked in the protected state, and sectors that are unprotected will be

locked in the unprotected state. These states cannot be changed as long as hardware locking is active, so the Pro-

tect Sector, Unprotect Sector, and Write Status Register commands will be ignored. In order to modify the

protection status of a sector, the WP pin must first be deasserted, and the SPRL bit in the Status Register must be

reset back to the logical “0” state using the Write Status Register command. When resetting the SPRL bit back to a

logical “0”, it is not possible to perform a Global Protect or Global Unprotect at the same time since the Sector Pro-

tection Registers remain soft-locked until after the Write Status Register command has been executed.

If the WP pin is permanently connected to GND, then once the SPRL bit is set to a logical “1”, the only way to reset

the bit back to the logical “0” state is to power-cycle the device. This allows a system to power-up with all sectors

software protected but not hardware locked. Therefore, sectors can be unprotected and protected as needed and

then hardware locked at a later time by simply setting the SPRL bit in the Status Register.

When the WP pin is deasserted, or if the WP pin is permanently connected to VCC, the SPRL bit in the Status Reg-

ister can still be set to a logical “1” to lock the Sector Protection Registers. This provides a software locking ability

to prevent erroneous Protect Sector or Unprotect Sector commands from being processed. When changing the

SPRL bit to a logical “1” from a logical “0”, it is also possible to perform a Global Protect or Global Unprotect at the

same time by writing the appropriate values into bits five, four, three, and two of the first byte of the Status

Tables 9-4 and 9-5 detail the various protection and locking states of the device.

Note:

1. “n” represents a sector number

Table 9-4.

Sector Protection Register States

Sector Protection Register

n(1)

Sector

n(1)

(Don't Care)

Unprotected

Protected

Table 9-5.

Hardware and Software Locking

SPRL

Locking

SPRL Change Allowed

Sector Protection Registers

Can be modified from 0 to 1

Unlocked and modifiable using the Protect and Unprotect

Sector commands. Global Protect and Unprotect can also be

performed.

Hardware

Locked

Locked in current state. Protect and Unprotect Sector

commands will be ignored. Global Protect and Unprotect

cannot be performed.

Can be modified from 0 to 1

Unlocked and modifiable using the Protect and Unprotect

Sector commands. Global Protect and Unprotect can also be

performed.

Software

Locked

Can be modified from 1 to 0

Locked in current state. Protect and Unprotect Sector

commands will be ignored. Global Protect and Unprotect

cannot be performed.

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