8

AT25FS040

5107D–SFLSH–09/06

protection employed. These bits are set by using the WRSR instruction. During internal

write cycles, all other commands will be ignored except the RDSR instruction.

READ PRODUCT ID (RDID): The RDID instruction allows the user to read the manufac-

turer ID byte followed by two device ID bytes. The manufacturer ID is assigned by

JEDEC and is 1Fh for Atmel (see Table 8). The first device ID byte indicates the mem-

ory type (66h=AT25FS040) followed by the device memory capacity byte (04h). For

maximum compatibility and flexibility, two RDID opcodes (9Fh and ABh) are supported

and will perform the same operation.

The device is first selected by driving Chip Select (CS) low then the RDID opcode is

shifted in on Serial In (SI) during rising edge of clock. The 24-bit Manufacturer and

Device Identification Codes stored in memory are clocked out on Serial Output (SO)

starting on the falling edge of clock (see Figure 15). If CS stays low after the last bit of

second device ID byte is shifted out, the manufacturer ID and 2 byte device ID will con-

tinue to be clocked out until CS goes high. The RDID sequence is terminated any time

CS is driven high and the device will go into standby mode.

WRITE STATUS REGISTER (WRSR): The WRSR instruction allows the user to select

one of eight levels of protection for the AT25FS040. The AT25FS040 is divided into

eight blocks where the top 1/64, 1/32, 1/16, 1/8, top quarter (1/4), top half (1/2), or all of

the memory blocks can be protected (locked out) from write. Any of the locked-out

blocks will therefore be READ only. The locked-out sector/block and the corresponding

status register control bits are shown in Table 9 on page 9.

Table 6. Status Register Format

Bit 7

Bit 6

Bit 5

Bit 4

Bit 3

Bit 2

Bit 1

Bit 0

WPEN

BP4

BP3

BP2

BP1

BP0

WEN

RDY

Table 7. Read Status Register Bit Definition

Bit

Definition

Bit 0 (RDY)

Bit 0 = 0 (RDY) indicates the device is READY. Bit 0 = 1 indicates the

write cycle is in progress.

Bit 1 (WEN)

Bit 1 = 0 indicates the device is not WRITE ENABLED. Bit 1 = 1 indicates

the device is WRITE ENABLED.

Bit 2 (BP0)

See Table 9.

Bit 3 (BP1)

See Table 9.

Bit 4 (BP2)

See Table 9.

Bit 5 (BP3)

See Table 9.

Bit 6 (BP4)

See Table 9.

Bit 7 (WPEN)

See Table 10.

Bits 0-7 are 1s during an internal write cycle.

Table 8. Read Product ID (RDID)

Manufacturer ID

Device ID

Memory Type

Memory Capacity

1Fh

66h

04h