AT25DF021 datasheet(17/41 Pages) ATMEL

17 / 41 page

3677D–DFLASH–04/09

AT25DF021

SPRL bit from a logical “1” to a logical “0” provided the WP pin is deasserted. Likewise, the sys-

tem can write an F0h to change the SPRL bit from a logical “0” to a logical “1” without affecting

the current sector protection status (no changes will be made to the Sector Protection

Registers).

When writing to the first byte of the Status Register, bits 5, 4, 3, and 2 will not actually be modi-

fied but will be decoded by the device for the purposes of the Global Protect and Global

Unprotect functions. Only bit 7, the SPRL bit, will actually be modified. Therefore, when reading

the first byte of the Status Register, bits 5, 4, 3, and 2 will not reflect the values written to them

but will instead indicate the status of the WP pin and the sector protection status. Please refer to

“Read Status Register” on page 22 and Table 11-1 on page 22 for details on the Status Register

format and what values can be read for bits 5, 4, 3, and 2.

9.6

Read Sector Protection Registers

The Sector Protection Registers can be read to determine the current software protection status

of each sector. Reading the Sector Protection Registers, however, will not determine the status

of the WP pin.

To read the Sector Protection Register for a particular sector, the CS pin must first be asserted

and the opcode of 3Ch must be clocked in. Once the opcode has been clocked in, three address

bytes designating any address within the sector must be clocked in. After the last address byte

has been clocked in, the device will begin outputting data on the SO pin during every subse-

quent clock cycle. The data being output will be a repeating byte of either FFh or 00h to denote

the value of the appropriate Sector Protection 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.

In addition to reading the individual Sector Protection Registers, the Software Protection Status

(SWP) bits in the Status Register can be read to determine if all, some, or none of the sectors

are software protected (refer to “Read Status Register” on page 22 for more details).

Figure 9-5.

Read Sector Protection Register

Table 9-3.

Read Sector Protection Register - Output Data

Output Data

Sector Protection Register Value

00h

Sector Protection Register value is 0 (sector is unprotected).

FFh

Sector Protection Register value is 1 (sector is protected).

SCK

MSB

00111100

410 11

812

37 38

31 32

29 30

39 40

OPCODE

AAAA

AAA

MSB

DDDDDDD

ADDRESS BITS A23-A0

DATA BYTE

HIGH-IMPEDANCE

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