at45db081d-su-sl955 ATMEL Corporation, at45db081d-su-sl955 Datasheet - Page 18

• Manufacturer Part Number: at45db081d-su-sl955
• Description: 8-megabit 2.5-volt Or 2.7-volt Dataflash
• Manufacturer: ATMEL Corporation

10. Security Features
10.1
Figure 10-1. Sector Lockdown
18
Sector Lockdown
AT45DB081D
CS
SI
Each transition
represents 8 bits
The device incorporates a Sector Lockdown mechanism that allows each individual sector to be
permanently locked so that it becomes read only. 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. Once a sector is locked down, it can never be erased or pro-
grammed, and it can never be unlocked.
To issue the Sector Lockdown command, the CS pin must first be asserted as it would be for
any other command. Once the CS pin has been asserted, the appropriate 4-byte opcode
sequence must be clocked into the device in the correct order. The 4-byte opcode sequence
must start with 3DH and be followed by 2AH, 7FH, and 30H. After the last byte of the command
sequence has been clocked in, then three address bytes specifying any address within the sec-
tor to be locked down must be clocked into the device. After the last address bit has been
clocked in, the CS pin must then be deasserted to initiate the internally self-timed lockdown
sequence.
The lockdown sequence should take place in a maximum time of t
Register will indicate that the device is busy. If the device is powered-down before the comple-
tion of the lockdown 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 reissue the Sector Lockdown com-
mand if necessary.
Opcode
Command
Sector Lockdown
Byte 1
Opcode
Byte 2
Opcode
Byte 3
Opcode
Byte 4
Byte 1
3DH
Address
Bytes
Byte 2
2AH
Address
Bytes
P
, during which time the Status
Address
Byte 3
Bytes
7FH
3596I–DFLASH–4/08
Byte 4
30H