AT25DF641 Datasheet, PDF (30/59 Pages) ATMEL Corporation – 64-Megabit 2.7-volt Minimum SPI Serial Flash Memory

the Sector Lockdown Registers can be made (see “Freeze Sector Lockdown State” below). 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 CS pin
has been deasserted.
Figure 10-1. Sector Lockdown
CS
SCK
SI
SO
0123456789
29 30 31 32 33 34 35 36 37 38 39
OPCODE
ADDRESS BITS A23-A0 CONFIRMATION BYTE IN
0 0 1 1 0 0 1 1AAA
MSB
MSB
AAA1 1 0 1 0 0 0 0
MSB
HIGH-IMPEDANCE
10.2
Freeze Sector Lockdown State
The current sector lockdown state can be permanently frozen so that no further modifications to
the Sector Lockdown Registers can be made; therefore, the Sector Lockdown command will be
permanently disabled, and no additional sectors can be locked down aside from those already
locked down. Any attempts to issue the Sector Lockdown command after the sector lockdown
state has been frozen will be ignored.
Before the Freeze Sector Lockdown State 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. To issue the Freeze Sector Lockdown State command, the
CS pin must first be asserted and the opcode of 34h must be clocked into the device followed by
three command specific address bytes of 55AA40h. After the three address bytes have been
clocked in, a confirmation byte of D0h must be clocked in immediately following the three
address bytes. Any additional data clocked into the device will be ignored. When the CS pin is
deasserted, the current sector lockdown state will be permanently frozen within a time of t_LOCK.
In addition, the WEL bit in the Status Register will be reset back to the logical “0” state, and the
SLE bit will be permanently reset to a logical “0” to indicate that the Sector Lockdown command
is permanently disabled.
The complete and correct three address bytes and the confirmation byte 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. When the
device aborts the Freeze Sector Lockdown State operation, the WEL bit in the Status Register
will be reset to a logical “0”; however, the state of the SLE bit will be unchanged.
30 AT25DF641 [Preliminary]
3680E–DFLASH–12/08