Technical Note

9/18

www.rohm.com

2010.12 - Rev.B

© 2010 ROHM Co., Ltd. All rights reserved.

3. Write command (WRITE)

By write command, data of EEPROM can be written. As for this command, set CSB LOW, then input address and data

after write ope code. Then, by making CSB HIGH, the EEPROM starts writing. The write time of EEPROM requires time

of tE/W (Max 5ms). During tE/W, other than read status register command is not accepted. Set CSB HIGH between

taking the last data (D0) and rising the next SCK clock. At the other timing, write command is not executed, and this write

command is cancelled. This IC has page write function, and after input of data for 1 byte (8 bits), by continuing data input

without setting CSB HIGH, 2byte or more data can be written for one tE/W. The maximum number of write bytes is

specified per device of each capacity. Up to 64 arbitrary bytes can be written (in the case of BR25S128/256-W). In page

write, the insignificant 5 bit of the designated address is incremented internally at every time when data of 1 byte is input

and data is written to respective addresses. When data of the maximum bytes or higher is input, address rolls over, and

previously input data is overwritten.

4. Write status register, Read status register command (WRSR/RDSR)

Write status register command can write data of status register. The data can be written by this command are 3 bits, that

is, WPEN(bit7), BP1 (bit3) and BP0 (bit2) among 8 bits of status register. By BP1 and BP0, write disable block of

EEPROM can be set. As for this command, set CSB LOW, and input ope code of write status register, and input data.

Then, by making CSB HIGH, EEPROM starts writing. Write time requires time of tE/W as same as write. As for CSB rise,

set CSB HIGH between taking the last data bit (bit0) and the next SCK clock rising. At the other timing, command is

cancelled. Write disable block is determined by BP1 BP0, and the block can be selected from 1/4 , 1/2, and entire of

memory array (Refer to the write disable block setting table.). To the write disabled block, write cannot be made, and only

read can be made.

Product

number

Address

length

BR25S320-W

A11-A0

BR25S640-W

A12-A0

BR25S128-W

A13-A0

BR25S256-W

A14-A0

High-Z

＊=Don't Care

31

D0

0

0

0

0

0

D2

D1

D7

23

30

24

D6

0

A0

A1

*

1

1

2

4

0

CSB

SCK

SI

SO

0

3

7

8

5

6

A12

～ ～

～ ～

～ ～

～ ～

～ ～

11

～ ～

～ ～

～ ～

～ ～

9

10

A13

A14

Fig.36

Write command

CSB

SCK

High-Z

*=Don't care

0

0

0

0

1

WPEN

0

1

2

4

0

SI

SO

0

3

7

8

5

6

*

9

10

11

12

13

14

15

*

*

BP1

BP0

*

*

bit7

bit6

bit5

bit4

bit3

bit2

bit1

bit0

0

Fig.37

Write status register

Fig.38

Read status register command

High-Z

bit7

bit6

bit5

bit4

0

0

0

bit3

bit2

bit1

bit0

13

CSB

SCK

SI

1

1

10

6

0

SO

14

1

2

WEN

R/B

11

15

3

7

9

0

5

12

0

0

0

0

0

4

8

WPEN

BP1 BP0