AT25DF641 datasheet(31/59 Pages) ATMEL

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3680E–DFLASH–12/08

AT25DF641 [Preliminary]

Figure 10-2. Freeze Sector Lockdown State

10.3

Read Sector Lockdown Registers

The Sector Lockdown Registers can be read to determine the current lockdown status of each

physical 64-Kbyte sector. To read the Sector Lockdown Register for a particular 64-Kbyte sec-

tor, the CS pin must first be asserted and the opcode of 35h must be clocked in. Once the

opcode has been clocked in, three address bytes designating any address within the 64-Kbyte

sector must be clocked in. After the address bytes have been clocked in, data will be output on

the SO pin during every subsequent clock cycle. The data being output will be a repeating byte

of either FFh or 00h to denote the value of the appropriate Sector Lockdown Register.

At clock frequencies above f

CLK, the first byte of data output will not be valid. Therefore, if operat-

ing at clock frequencies above f

CLK, at least two bytes of data must be clocked out from the

device in order to determine the correct status of the appropriate Sector Lockdown Register.

Deasserting the CS pin will terminate the read operation and put the SO pin into a high-imped-

ance state. The CS pin can be deasserted at any time and does not require that a full byte of

data be read.

Figure 10-3. Read Sector Lockdown Register

SCK

MSB

00110100

839

37 38

31 32

29 30

OPCODE

HIGH-IMPEDANCE

000

MSB

1101000

ADDRESS BITS A23-A0 CONFIRMATION BYTE IN

Table 10-2.

Read Sector Lockdown Register – Output Data

Output Data

Sector Lockdown Register Value

00h

Sector Lockdown Register value is 0 (sector is not locked down).

FFh

Sector Lockdown Register value is 1 (sector is permanently locked down).

SCK

MSB

00110101

410 11

812

42 43

37 38

31 32

29 30

47 48

OPCODE

AAAA

AAA

A A

MSB

XXXXXXX X

MSB

DDDDDDD D

ADDRESS BITS A23-A0

DON'T CARE

DATA BYTE

HIGH-IMPEDANCE

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