at25df041a ATMEL Corporation, at25df041a Datasheet - Page 15

• Manufacturer Part Number: at25df041a
• Description: 4-megabit 2.3-volt Or 2.7-volt Minimum Spi Serial Flash Memory
• Manufacturer: ATMEL Corporation

9. Protection Commands and Features
9.1
9.2
3668C–DFLASH–3/08
Write Enable
Write Disable
The Write Enable command is used to set the Write Enable Latch (WEL) bit in the Status Regis-
ter to a logical “1” state. The WEL bit must be set before a program, erase, Protect Sector,
Unprotect Sector, or Write Status Register command can be executed. This makes the issuance
of these commands a two step process, thereby reducing the chances of a command being
accidentally or erroneously executed. If the WEL bit in the Status Register is not set prior to the
issuance of one of these commands, then the command will not be executed.
To issue the Write Enable command, the CS pin must first be asserted and the opcode of 06h
must be clocked into the device. No address bytes need to be clocked into the device, and any
data clocked in after the opcode will be ignored. When the CS pin is deasserted, the WEL bit in
the Status Register will be set to a logical “1”. The complete opcode must be clocked into the
device before the CS pin is deasserted, and the CS pin must be deasserted on an even byte
boundary (multiples of eight bits); otherwise, the device will abort the operation and the state of
the WEL bit will not change.
Figure 9-1.
The Write Disable command is used to reset the Write Enable Latch (WEL) bit in the Status Reg-
ister to the logical “0” state. With the WEL bit reset, all program, erase, Protect Sector, Unprotect
Sector, and Write Status Register commands will not be executed. The Write Disable command
is also used to exit the Sequential Program Mode. Other conditions can also cause the WEL bit
to be reset; for more details, refer to the WEL bit section of the Status Register description.
To issue the Write Disable command, the CS pin must first be asserted and the opcode of 04h
must be clocked into the device. No address bytes need to be clocked into the device, and any
data clocked in after the opcode will be ignored. When the CS pin is deasserted, the WEL bit in
the Status Register will be reset to a logical “0”. The complete opcode must be clocked into the
device before the CS pin is deasserted, and the CS pin must be deasserted on an even byte
boundary (multiples of eight bits); otherwise, the device will abort the operation and the state of
the WEL bit will not change.
Write Enable
SCK
SO
CS
SI
HIGH-IMPEDANCE
MSB
0
0
0
1
AT25DF041A [Preliminary]
0
2
OPCODE
0
3
0
4
1
5
1
6
0
7
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