at25df321a ATMEL Corporation, at25df321a Datasheet - Page 21

• Manufacturer Part Number: at25df321a
• Description: 32-megabit 2.7-volt Minimum Spi Serial Flash Memory
• Manufacturer: ATMEL Corporation

9. Protection Commands and Features
9.1
3686C–DFLASH–12/08
Write Enable
Figure 8-8.
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 Byte/Page Program, erase, Protect
Sector, Unprotect Sector, Sector Lockdown, Freeze Sector Lockdown State, Program OTP
Security Register, 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.
Program/Erase Resume
Write Enable
SCK
SCK
SO
SO
CS
CS
SI
SI
HIGH-IMPEDANCE
HIGH-IMPEDANCE
MSB
MSB
1
0
0
0
1
0
1
1
AT25DF321A [Preliminary]
0
0
2
2
OPCODE
OPCODE
1
0
3
3
0
0
4
4
0
1
5
5
0
1
6
6
0
0
7
7
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