9

AT25FS040

5107D–SFLSH–09/06

The six bits, BP0, BP1, BP2, BP3, BP4 and WPEN, are nonvolatile cells that have the

same properties and functions as the regular memory cells.

Note:

1. x = don’t care

The WRSR instruction also allows the user to enable or disable the Write Protect (WP)

pin through the use of the Write Protect Enable (WPEN) bit. Hardware write protection is

enabled when the WP pin is low and the WPEN bit is “1”. Hardware write protection is

disabled when either the WP pin is high or the WPEN bit is “0.” When the device is hard-

ware write protected, writes to the Status Register, including the Block Protect bits and

the WPEN bit, and the locked-out sectors in the memory array are disabled. Write is

only allowed to sectors of the memory which are not locked out. The WRSR instruction

is self-timed to automatically erase and program BP0, BP1, BP2, BP3, BP4 and WPEN

bits. In order to write the status register, two separate instructions must be executed.

First, the device must be write enabled via the WREN instruction. Then, CS must be low

and the WRSR instruction and data for the six bits are entered. The WRSR write cycle

will begin once CS goes high. During the internal write cycle, all instructions will be

ignored except RDSR instructions. The AT25FS040 will automatically return to write dis-

able state at the completion of the WRSR cycle. The status register is factory

programmed to all 0’s.

Note:

When the WPEN bit is hardware write protected, it cannot be changed back to “0”, as

long as the WP pin is held low.

Table 9. Sector/Block Write Protect Bits

Level

Status Register Bits

AT25FS040

BP4

BP3

BP2

BP1

BP0

Array Address

locked Out

Locked-out

Blocks

0(none)

0

0

0

0

0

None

None

1(1/64)

0

1

0

0

0

07E000H - 07FFFFH

Sector 15-16 of Block 8

2(1/32)

1

0

0

0

0

07C000H - 07FFFFH

Sector 13-16 of Block 8

3(1/16)

1

1

0

0

0

078000H - 07FFFFH

Sector 9-16 of Block 8

4(1/8)

x

x

0

0

1

070000H - 07FFFFH

All sectors of Block 8

5(1/4)

x

x

0

1

0

060000H - 07FFFFH

All Sectors of Block 7,8

6(1/2)

x

x

0

1

1

040000H - 07FFFFH

All Sectors of Block 5,6,7,8

7(ALL)

x

x

1

x

x

000000H - 07FFFFH

All Sectors of All Blocks (1-8)

Table 10. WPEN Operation

WPEN

WP

WEN

ProtectedBlocks

UnprotectedBlocks

Status Register

0

X

0

Protected

Protected

Protected

0

X

1

Protected

Writable

Writable

1

Low

0

Protected

Protected

Protected

1

Low

1

Protected

Writable

Protected

X

High

0

Protected

Protected

Protected

X

High

1

Protected

Writable

Writable