9
AT45DB1282
2472C–DFLSH–11/03
Security Register The AT45DB1282 contains a specialized register that can be used for security purposes
in system design. The Security Register is a unique 128-byte register that is divided into
two portions. The first 64 bytes (byte 0 to byte 63) of this register are allocated as a one-
time user programmable space. Once these 64 bytes have been programmed, they
should not be reprogrammed. The remaining 64 bytes of this register (byte 64 to byte
127) are factory programmed by Atmel and will contain a unique number for each
device. The factory programmed data is fixed and cannot be changed.
The Security Register can be read by clocking in opcode 77H to the device followed by
four address bytes (which are comprised of 21 don’t care bits plus 11 byte address bits)
and a series of don’t care clock cycles (24 if using the serial interface and 19 if using the
8-bit interface). The Security Register Read can be terminated by asserting CS
low to
high after the 128-byte security register has been read out. The continuation of clocking
past that will result in indeterminate data on the output. See the opcode table on page
13 for this mode.
To program the first 64 bytes of the Security Register, a two step sequence must be
used. The first step requires that the user loads the desired data into Buffer 1 by using
the Buffer 1 Write operation (opcode 84H – see Buffer Write description). The user
should specify the starting buffer address as location zero and should write a full
64 bytes of information into the buffer. Otherwise, the first 64 bytes of the buffer may
contain data that was previously stored in the buffer. It is not necessary to fill the remain-
ing 992 bytes (byte locations 64 through 1055) of the buffer with data. After the Buffer 1
Write operation has been completed, the Security Register can be subsequently pro-
grammed by reselecting the device and clocking in opcode 9AH into the device followed
by four don’t care bytes (32 clock cycles if using the serial interface and four clock
cycles if using the 8-bit interface). After the final don’t care clock cycle has been
completed, a low-to-high transition on the CS
pin will cause the device to initiate an
internally self-timed program operation in which the contents of Buffer 1 will be pro-
grammed into the Security Register. Only the first 64 bytes of data in Buffer 1 will be
programmed into the Security Register; the remaining 992 bytes of the buffer will be
ignored. The Security Register program operation should take place in a maximum time
of t
P
.
Operation Mode
Summary
The modes described can be separated into two groups – modes that make use of the
Flash memory array (Group A) and modes that do not make use of the Flash memory
array (Group B).
Group A modes consist of:
1. Main Memory Page Read
2. Continuous Array Read
3. Main Memory Page to Buffer 1 (or 2) Transfer
4. Main Memory Page to Buffer 1 (or 2) Compare
5. Buffer 1 (or 2) to Main Memory Page Program
6. Page Erase
7. Block Erase
Group B modes consist of:
1. Buffer 1 (or 2) Read
2. Buffer 1 (or 2) Write
3. Status Register Read
