AT25DF641A-MH-T ATMEL [ATMEL Corporation], AT25DF641A-MH-T Datasheet - Page 31

• Manufacturer Part Number: AT25DF641A-MH-T
• Description: 64-Mbit 2.7V Minimum Serial Peripheral Interface Serial Flash Memory
• Manufacturer: ATMEL [ATMEL Corporation]

10.4
8693A–DFLASH–8/10
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 por-
tions. 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 Atmel and will contain a unique value for
each device. The factory programmed data is fixed and cannot be changed.
Table 10-3.
The user-programmable portion of the OTP Security Register does not need to be erased before
it is programmed. In addition, the Program OTP Security Register command operates on the
entire 64-byte user-programmable portion of the OTP Security Register at one time. Once the
user-programmable space has been programmed with any number of bytes, the user-program-
mable space cannot be programmed again; therefore, it is not possible to only program the first
two bytes of the register and then program the remaining 62-bytes at a later time.
Before the Program OTP Security Register command can be issued, the Write Enable command
must have been previously issued to set the WEL bit in the Status Register to a logical “1”. To
program the OTP Security Register, the CS pin must first be asserted and an opcode of 9Bh
must be clocked into the device followed by the three address bytes denoting the first byte loca-
tion of the OTP Security Register to begin programming at. Since the size of the user-
programmable portion of the OTP Security Register is 64-bytes, the upper order address bits do
not need to be decoded by the device. Therefore, address bits A23-A6 will be ignored by the
device and their values can be either a logical “1” or “0”. After the address bytes have been
clocked in, data can then be clocked into the device and will be stored in the internal buffer.
If the starting memory address denoted by A23-A0 does not start at the beginning of the OTP
Security Register memory space (A5-A0 are not all 0), then special circumstances regarding
which OTP Security Register locations to be programmed will apply. In this situation, any data
that is sent to the device that goes beyond the end of the 64-byte user-programmable space will
wrap around back to the beginning of the OTP Security Register. For example, if the starting
address denoted by A23-A0 is 00003Eh, and three bytes of data are sent to the device, then the
first two bytes of data will be programmed at OTP Security Register addresses 00003Eh and
00003Fh while the last byte of data will be programmed at address 000000h. The remaining
bytes in the OTP Security Register (addresses 000001h through 00003Dh) will not be pro-
grammed and will remain in the erased state (FFh). In addition, if more than 64-bytes of data are
sent to the device, then only the last 64-bytes sent will be latched into the internal buffer.
When the CS pin is deasserted, the device will take the data stored in the internal buffer and pro-
gram it into the appropriate OTP Security Register locations based on the starting address
specified by A23-A0 and the number of data bytes sent to the device. If less than 64-bytes of
data were sent to the device, then the remaining bytes within the OTP Security Register will not
0
One-Time User Programmable
1
OTP Security Register
. . .
Atmel AT25DF641A [Preliminary]
62
Security Register
Byte Number
63
64
Factory Programmed by Atmel
65
. . .
126
127
31