AT25DF081A datasheet(28/54 Pages) ETC2

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8715C–SFLSH–1/2013

AT25DF081A

10.4 Program OTP Security Register

The device contains a specialized OTP (One-Time Programmable) Security Register that can be used for pur-

poses 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 portions. The first 64-bytes (byte locations 0 through 63) of the OTP Secu-

rity 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 Adesto and will contain a unique value for each device. The factory pro-

grammed 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 por-

tion of the OTP Security Register at one time. Once the user-programmable space has been programmed with any

number of bytes, the user-programmable 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 location 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 exam-

ple, 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 programmed and will remain in the erased state (FFh). In addi-

tion, 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 program 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 be programmed and will remain in the erased state (FFh). The programming of

the data bytes is internally self-timed and should take place in a time of tOTPP. It is not possible to suspend the pro-

gramming of the OTP Security Register.

Table 10-3.

OTP Security Register

Security Register

Byte Number

. . .

126

127

One-Time User Programmable

Factory Programmed by Adesto

AT25DF081A Datasheet(PDF) 28 Page - List of Unclassifed Manufacturers

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