25LC640-E/ST MICROCHIP [Microchip Technology], 25LC640-E/ST Datasheet - Page 9

• Manufacturer Part Number: 25LC640-E/ST
• Description: 64K SPI Bus Serial EEPROM
• Manufacturer: MICROCHIP [Microchip Technology]

3.4
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.
FIGURE 3-4:
FIGURE 3-5:
 2004 Microchip Technology Inc.
Write Enable (WREN) and
Write Disable (WRDI)
WRITE ENABLE SEQUENCE
WRITE DISABLE SEQUENCE
SCK
SCK
CS
CS
SO
SO
SI
SI
0
0
0
0
0
0
1
1
High-impedance
High-impedance
0
0
2
2
0
0
3
3
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
0
0
4
4
25AA640/25LC640
1
1
5
5
1
1 0
6
6
0
0
7
7
DS21223G-page 9