AT25DF641_13 datasheet(32/56 Pages) ETC2

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AT25DF641

3680F–DFLASH–4/10

Table 9-4.

OTP Security Register

Security Register

Byte Number

. . .

126

127

One-Time User Programmable

Factory Programmed by Adesto

The user-programmable portion of the OTP Security Register does not need to be er ased before it is

programmed. In addition, the Program OTP Security Register command operates on t he 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-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

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

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

(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

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). T he

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 programming of the OTP Security Register.

The three address bytes and at least one complete byte of data must be clocked into the device before the

is deasserted, and the

pin must be deasserted on even byte boundaries (multiples of eight bits); otherwise, the

device will abort the operation and the user-programmable portion of the OTP Security Register will not be

programmed. The WEL bit in the Status Register will be reset back to the logical “0” state if the OTP Security

the

pin being deasserted on uneven byte boundaries, or because the user-programmable portion of the OTP

Security Register was previously programmed.

While the device is programming the OTP Security Register, the Status Register can be read and will indicate that

the device is busy. For faster throughput, it is recommended that the Status Register be polled rather than waiting

the tOTPP time to determine if the data bytes have finished programming. At some point before the OTP Security

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