8

AT25010A/020A/040A

5087B–SEEPR–1/05

the data within any selected segment will therefore be read only. The block write protec-

tion levels and corresponding status register control bits are shown in Table 8.

Bits BP0 and BP1 are nonvolatile cells that have the same properties and functions as

READ SEQUENCE (READ): Reading the AT25010A/020A/040A via the serial output

(SO) pin requires the following sequence. After the CS line is pulled low to select a

device, the read op-code (including A8) is transmitted via the SI line followed by the byte

address to be read (A7–A0). Upon completion, any data on the SI line will be ignored.

The data (D7

−D0) at the specified address is then shifted out onto the SO line. If only

one byte is to be read, the CS line should be driven high after the data comes out. The

read sequence can be continued since the byte address is automatically incremented

and data will continue to be shifted out. When the highest address is reached, the

address counter will roll over to the lowest address, allowing the entire memory to be

read in one continuous read cycle.

WRITE SEQUENCE (WRITE): In order to program the AT25010A/020A/040A, the Write

Protect (WP) pin must be held high and two separate instructions must be executed.

First, the device

instruction may be executed. Also, the address of the memory location(s) to be pro-

grammed must be outside the protected address field location selected by the block

write protection level. During an internal write cycle, all commands will be ignored

except the RDSR instruction.

A write instruction requires the following sequence. After the CS line is pulled low to

select the device, the WRITE op-code (including A8) is transmitted via the SI line fol-

lowed by the byte address (A7

−A0) and the data (D7–D0) to be programmed.

Programming will start after the CS pin is brought high. The low-to-high transition of the

CS pin must occur during the SCK low-time immediately after clocking in the D0 (LSB)

data bit.

The READY/BUSY status of the device can be determined by initiating a read status

register (RDSR) instruction. If Bit 0 = “1”, the write cycle is still in progress. If Bit 0 = “0”,

the write cycle has ended. Only the RDSR instruction is enabled during the write pro-

gramming cycle.

The AT25010A/020A/040A is capable of an 8-byte page write operation. After each byte

of data is received, the three low-order address bits are internally incremented by one;

the six high-order bits of the address will remain constant. If more than eight bytes of

data are transmitted, the address counter will roll over and the previously written data

will be overwritten. The AT25010A/020A/040A is automatically returned to the write dis-

able state at the completion of a write cycle.

NOTE: If the WP pin is brought low or if the device is not write enabled (WREN), the

device will ignore the Write instruction and will return to the standby state when CS is

brought high. A new CS falling edge is required to reinitiate the serial communication.

Table 8. Block Write Protect Bits

Level

Status Register Bits

Array Addresses Protected

BP1

BP0

AT25010A

AT25020A

AT25040A

0

0

0

None

None

None

1 (1/4)

0

1

60-7F

C0-FF

180-1FF

2 (1/2)

1

0

40-7F

80-FF

100-1FF

3 (All)

1

1

00-7F

00-FF

000-1FF