AT25DF641_13 datasheet(29/56 Pages) ETC2

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AT25DF641

3680F–DFLASH–4/10

Before the Sector Lockdown command can be issued, the Write Enable command must have been previously

issued to set the WEL bit in the Status Register to a logical “1”. In addition, the Sector Lockdown Enabled (SLE)

bit in the Status Register must have also been previously set to the logical “1” state by using the Write Status

command, the

pin must first be asserted and the opcode of 33h must be clocked into the device followed by

three address bytes designating any address within the 64-Kbyte sector to be locked down. After the three

address bytes have been clocked in, a confirmation byte of D0h must also be clocked in immediately following the

three address bytes. Any additional data clocked into the device after the first byte of data will be ignored. When

the

pin is deasserted, the Sector Lockdown Register corresponding to the sector addressed by A23-A0 will be

set to the logical “1” state, and the sector itself will then be permanently locked down from program and erase

operations within a time of tLOCK. In addition, the WEL bit in the Status Register will be reset back to the logical “0”

state.

The complete three address bytes and the correct confirmation byte value of D0h must be clocked into the device

before the

pin is deasserted, and the

pin must be deasserted on an even byte boundary (multiples of eight

bits); otherwise, the device will abort the operation. When the device aborts the Sector Lockdown operation, the

state of the corresponding Sector Lockdown Register as well as the SLE bit in the Status Register will be

unchanged; however, the WEL bit in the Status Register will be reset to a logical “0”.

As a safeguard against accidental or erroneous locking down of sectors, the Sector Lockdown command can be

enabled and disabled as needed by using the SLE bit in the Status Register. I n addition, the current sector

lockdown state can be frozen so that no further modifications to the Sector Lockdown Registers can be made

(see “Freeze Sector Lockdown State”). If the Sector Lockdown command is disabled or if the sector lockdown

state is frozen, then any attempts to issue the Sector Lockdown command will be ignored, and the device will

reset the WEL bit in the Status Register back to a logical “0” and return to the idle state once the

pin has been

deasserted.

Figure 9-1.

Sector Lockdown

SCK

MS B

37 38

31 32

29 30

OP C ODE

HIG H-IMP E DANC E

MS B

ADDR E S S B ITS A23-A0 C ONF IR MATION B Y TE IN

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