AT45DB321E datasheet(23/73 Pages) ETC2

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AT45DB321E

8784F–DFLASH–11/2013

Security Features

8.1

Sector Lockdown

The device incorporates a sector lockdown mechanism that allows each individual sector to be permanently locked so

that it becomes read-only (ROM). This is useful for applications that require the ability to permanently protect a number of

sectors against malicious attempts at altering program code or security information.

Warning:

Once a sector is locked down, it can never be erased or programmed, and it can never be unlocked.

To issue the sector lockdown command, a 4-byte command sequence of 3Dh, 2Ah, 7Fh, and 30h must be clocked into

the device followed by three address bytes specifying any address within the sector to be locked down. After the last

address bit has been clocked in, the CS pin must be deasserted to initiate the internally self-timed lockdown sequence.

The lockdown sequence should take place in a maximum time of tP. During this time, the RDY/BUSY bit in the Status

sequence, then the lockdown status of the sector cannot be guaranteed. In this case, it is recommended that the user

read the Sector Lockdown Register to determine the status of the appropriate sector lockdown bits or bytes and re-issue

the Sector Lockdown command if necessary.

Table 8-1.

Sector Lockdown Command

Figure 8-1. Sector Lockdown

8.1.1

Read Sector Lockdown Register

The nonvolatile Sector Lockdown Register specifies which sectors in the main memory are currently unlocked or have

been permanently locked down. The Sector Lockdown Register is a read-only register and contains 64 bytes of data

which correspond to Sectors 0 through 63. To read the Sector Lockdown Register, an opcode of 35h must be clocked

into the device followed by three dummy bytes. After the last bit of the opcode and dummy bytes have been clocked in,

the data for the contents of the Sector Lockdown Register will be clocked out on the SO pin. The first byte (byte

location 0) corresponds to Sector 0 (0a and 0b), the second byte corresponds to Sector 1, and the last byte (byte location

63) corresponds to Sector 63. After the last byte of the Sector Lockdown Register has been read, additional pulses on

the SCK pin will result in undefined data being output on the SO pin.

Deasserting the CS pin will terminate the Read Sector Lockdown Register operation and put the SO pin into a

high-impedance state. Table 8-2 details the format the Sector Lockdown Register.

Table 8-2.

Sector Lockdown Register

Command

Byte 1

Byte 2

Byte 3

Byte 4

Sector Lockdown

3Dh

2Ah

7Fh

30h

3Dh

2Ah

7Fh

30h

Address

byte

Address

byte

Address

byte

Each transition represents eight bits

Sector Number

0 (0a, 0b)

1 to 63

Locked

See Table 8-3

FFh

Unlocked

00h

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