AT25DF641_13 datasheet(31/56 Pages) ETC2

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AT25DF641

3680F–DFLASH–4/10

9.3.

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 sector, the

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 c locked 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 fCLK, the first byte of data output will not be v alid. Therefore, if operating at clock

frequencies above fCLK, 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.

Table 9-3.

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)

Deasserting the

pin will terminate the read operation and put the SO pin into a high-impedance state. The

pin can be deasserted at any time and does not require that a full byte of data be read.

Figure 9-3.

Read Sector Lockdown Register

SCK

MS B

10 11

42 43

37 38

31 32

29 30

47 48

OPCODE

A A A A

A A A

A A

MS B

D D D D D D D D

ADDR E S S BITS A23-A0

DON'T CAR E

DATA BYTE

HIGH-IMPE DANCE

9.4.

Program OTP Security Register

The device contains a s pecialized OTP (One-Time Programmable) Security Register that can be used for

purposes such as unique device serialization, system-level Electronic Serial Number (ESN) storage, locked key

storage, etc. The OTP Security Register is independent of the main Flash memory array and is comprised of a

total of 128-bytes of memory divided into two portions. The first 64-bytes (byte locations 0 through 63) of the OTP

Security Register are allocated as a one-time user-programmable space. Once these 64-bytes have been

programmed, they cannot be erased or reprogrammed. The remaining 64-bytes of the OTP Security Register

(byte locations 64 through 127) are factory programmed by Adesto® and will contain a unique value for each

device. The factory programmed data is fixed and cannot be changed.

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