AT25DF161 datasheet(32/60 Pages) ATMEL

32 / 60 page

3687C–DFLASH–7/09

AT25DF161 [Preliminary]

10.4 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.

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

Table 10-3.

OTP Security Register

Security Register

Byte Number

. . .

126

127

One-Time User Programmable

Factory Programmed by Atmel

AT25DF161 数据表(PDF) 32 Page - ATMEL Corporation

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