Rainbow Electronics AT45DB021D - Manual (Page 11)

11
3638K–DFLASH–11/2012
AT45DB021D
6.1.2 Disable Sector Protection Command
To disable the sector protection using the software controlled method, the CS pin must first be asserted as it would
be with any other command. Once the CS pin has been asserted, the appropriate 4-byte sequence for the Disable
Sector Protection command must be clocked in via the input pin (SI). After the last bit of the command sequence
has been clocked in, the CS pin must be deasserted after which the sector protection will be disabled. The WP pin
must be in the deasserted state; otherwise, the Disable Sector Protection command will be ignored.
Table 6-2. Disenable Sector Protection Command
Figure 6-2. Disable Sector Protection
6.1.3 Various Aspects About Software Controlled Protection
Software controlled protection is useful in applications in which the WP pin is not or cannot be controlled by a host
processor. In such instances, the WP pin may be left floating (the WP pin is internally pulled high) and sector
protection can be controlled using the Enable Sector Protection and Disable Sector Protection commands.
If the device is power cycled, then the software controlled protection will be disabled. Once the device is powered
up, the Enable Sector Protection command should be reissued if sector protection is desired and if the WP pin is
not used.
7. Hardware Controlled Protection
Sectors specified for protection in the Sector Protection Register and the Sector Protection Register itself can be
protected from program and erase operations by asserting the WP pin and keeping the pin in its asserted state.
The Sector Protection Register and any sector specified for protection cannot be erased or reprogrammed as long
as the WP pin is asserted. In order to modify the Sector Protection Register, the WP pin must be deasserted. If the
WP pin is permanently connected to GND, then the content of the Sector Protection Register cannot be changed.
If the WP pin is deasserted, or permanently connected to V
CC
, then the content of the Sector Protection Register
can be modified.
The WP pin will override the software controlled protection method but only for protecting the sectors. For example,
if the sectors were not previously protected by the Enable Sector Protection command, then simply asserting the
WP pin would enable the sector protection within the maximum specified t
WPE
time. When the WP pin is
deasserted; however, the sector protection would no longer be enabled (after the maximum specified t
WPD
time) as
long as the Enable Sector Protection command was not issued while the WP pin was asserted. If the Enable
Sector Protection command was issued before or while the WP pin was asserted, then simply deasserting the WP
pin would not disable the sector protection. In this case, the Disable Sector Protection command would need to be
issued while the WP pin is deasserted to disable the sector protection. The Disable Sector Protection command is
also ignored whenever the WP pin is asserted.
A noise filter is incorporated to help protect against spurious noise that may inadvertently assert or deassert the
WP pin.
Command Byte 1 Byte 2 Byte 3 Byte 4
Disable Sector Protection 3DH 2AH 7FH 9AH
Opcode
Byte 1
Opcode
Byte 2
Opcode
Byte 3
Opcode
Byte 4
CS
Each transition
represents 8 bits
SI