AT25DF021 datasheet(21/41 Pages) ATMEL

21 / 41 page

3677D–DFLASH–04/09

AT25DF021

Figure 10-1. Program OTP Security Register

10.2 Read OTP Security Register

The OTP Security Register can be sequentially read in a similar fashion to the Read Array oper-

ation up to the maximum clock frequency specified by fCLK. To read the OTP Security Register,

the CS pin must first be asserted and the opcode of 77h must be clocked into the device. After

the opcode has been clocked in, the three address bytes must be clocked in to specify the start-

ing address location of the first byte to read within the OTP Security Register. Following the

three address bytes, two dummy bytes must be clocked into the device before data can be

output.

After the three address bytes and the dummy bytes have been clocked in, additional clock

cycles will result in OTP Security Register data being output on the SO pin. When the last byte

(00007Fh) of the OTP Security Register has been read, the device will continue reading back at

the beginning of the register (000000h). No delays will be incurred when wrapping around from

the end of the register to the beginning of the register.

Deasserting the CS pin will terminate the read operation and put the SO pin into a high-imped-

ance state. The CS pin can be deasserted at any time and does not require that a full byte of

data be read.

Figure 10-2. Read OTP Security Register

SCK

MSB

10011011

839

37 38

31 32

29 30

OPCODE

HIGH-IMPEDANCE

AAA

MSB

DDDDDDD

ADDRESS BITS A23-A0

DATA IN BYTE 1

MSB

DDDDDDD

DATA IN BYTE n

SCK

MSB

01110111

410 11

812

31 32

29 30

OPCODE

AAAA

AAA

MSB

DDDDDDD

ADDRESS BITS A23-A0

MSB

XXXXX

DON'T CARE

DATA BYTE 1

HIGH-IMPEDANCE

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