AT25DF321A datasheet(27/53 Pages) ETC2

27 / 53 page

3686F–DFLASH–1/2014

AT25DF321A

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 sector, 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 fCLK, the first byte of data output will not be valid. 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.

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

10.4

Program OTP Security Register

The device contains a specialized 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.

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

MSB

XXXXXXX

MSB

DDDDDDD

ADDRESS BITS A23-A0

DON'T CARE

DATA BYTE

HIGH-IMPEDANCE

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