Rainbow Electronics AT25DQ321 - Manual (Page 31)

31 AT25DQ321 [DATASHEET]
8718D–DFLASH–12/2012
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 Logical 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 Protect 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 Protection 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 V
CC
, the SPRL bit in the Status Register
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 5, 4, 3, and 2 of the first byte of the Status Register.
Tables 9-4 and 9-5 detail the various protection and locking states of the device.
Note: 1. “n” represents a sector number.
Table 9-5. Hardware and Software Locking
Table 9-4. Sector Protection Register States
WP
Sector Protection Register
n (1)
Sector
n (1)
X
(Don't Care)
0 Unprotected
1 Protected
WP SPRL Locking
SPRL Change
Allowed Sector Protection Registers
0 0
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.
0 1
Hardware
Locked
Locked
Locked in current state. Protect and Unprotect Sector commands will
be ignored. Global Protect and Unprotect cannot be performed.
1 0
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.
1 1
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.