AT26F004_06 Datasheet, PDF (18/38 Pages) ATMEL Corporation – 4-megabit 2.7-volt Only Serial Firmware DataFlash Memory

9.6 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 sta-
tus 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.
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 or reset 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 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 com-
mands from being processed.
Tables 9-3 and 9-4 detail the various protection and locking states of the device.
Table 9-3. Software Protection
Sector Protection Register
WP
n⁽¹⁾
X
0
(Don't Care)
1
Sector
n⁽¹⁾
Unprotected
Protected
Note: 1. “n” represents a sector number
Table 9-4. Hardware and Software Locking
WP SPRL Locking
SPRL
0
0
–
Can be modified from
0 to 1
Hardware
0
1
locked
Locked
1
0
–
Can be modified from
0 to 1
1
1
Software _{Can be modified from}
locked
1 to 0
Sector Protection Registers
Unlocked and modifiable using the Protect and
Unprotect Sector commands
Locked in current state. Protect and Unprotect
Sector commands will be ignored.
Unlocked and modifiable using the Protect and
Unprotect Sector commands
Locked in current state. Protect and Unprotect
Sector commands will be ignored.
18 AT26F004
3588C–DFLASH–04/06