25C640 Microchip Technology, Inc., 25C640 Datasheet - Page 10

• Manufacturer Part Number: 25C640
• Description: The 25AA640 is a 64K-bit Serial Electrically Erasable Prom With Memory Accessed Via a Simple Serial Peripheral Interface (SPI™) Compatible Serial Bus
• Manufacturer: Microchip Technology, Inc.

25AA640/25LC640
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:
DS21223E-page 10
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
1
1
5
5
1
1 0
6
6
0
0
7
7
2001 Microchip Technology Inc.