X25642/X25642S pdf datasheet (

The X25642 is a CMOS 65,536-bit serial E
2
PROM,
internally organized as 8K x 8. The X25642 features a
Serial Peripheral Interface (SPI) and software protocol
allowing operation on a simple three-wire bus. The bus
signals are a clock input (SCK) plus separate data in
(SI) and data out (SO) lines. Access to the device is
controlled through a chip select (CS) input, allowing
any number of devices to share the same bus.
The X25642 also features two additional inputs that
provide the end user with added flexibility. By
asserting the HOLD input, the X25642 will ignore transitions
on its inputs, thus allowing the host to service
higher priority interrupts. The WP input can be used as
a hardwire input to the X25642 disabling all write
attempts to the status register, thus providing a mechanism
for limiting end user capability of altering 0, 1/4,
1/2 or all of the memory.
The X25642 utilizes Xicor’s proprietary Direct Write
TM
cell, providing a minimum endurance of 100,000
cycles and a minimum data retention of 100 years.