25AA640/25LC640/25C640

DS21223A-page 8

Preliminary

© 1997 Microchip Technology Inc.

3.4

Write Enable (WREN) and Write

Disable (WRDI)

The 25xx640 contains a write enable latch.

See

Table 3-3 for the Write Protect Functionality Matrix.

This latch must be set before any write operation will

be completed internally. The WREN instruction will set

the latch, and the WRDI will reset the latch.

The following is a list of conditions under which the

write enable latch will be reset:

• Power-up

• WRDI instruction successfully executed

• WRSR instruction successfully executed

• WRITE instruction successfully executed

FIGURE 3-4:

WRITE ENABLE SEQUENCE

FIGURE 3-5:

WRITE DISABLE SEQUENCE

SCK

0

2

3

4

5

6

7

1

SI

high impedance

SO

CS

0

1

0

0

0

0

0

1

SCK

0

2

3

4

5

6

7

1

SI

high impedance

SO

CS

0

1

0

0

0

0

0

10