Rainbow Electronics AT45DB041E - Manual (Page 23)

23 AT45DB041E [ADVANCE DATASHEET]
8783B–DFLASH–11/2012
8. 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 t
P
. During this time, the RDY/BUSY bit in the Status
Register will indicate that the device is busy. If the device is powered-down before the completion 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 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 eight bytes of data
which correspond to Sectors 0 through 7. 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
7) corresponds to Sector 7. 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
CS
Address
byte
Address
byte
Address
byte
SI
Each transition represents eight bits
Sector Number 0 (0a, 0b) 1 to 7
Locked
See Table 8-3
FFh
Unlocked 00h