General Description
The NM25C640 is a 65,536-bit CMOS EEPROM with an SPI compatible serial interface. The NM25C640 is designed for data storage in applications requiring both non-volatile memory and insystem data updates. This EEPROM is well suited for applications using the 68HC11 series of microcontrollers that support the SPI interface for high speed communication with peripheral devices via a serial bus to reduce pin count. The NM25C640 is implemented in Fairchild Semiconductor’s floating gate CMOS process that provides superior endurance and data retention.

Features
■ 2.75 MHz clock rate @ 4.5V to 5.5V 2.1 MHz @ 2.7V to 4.5V
■ 65,536 bits organized as 8,192 x 8
■ Multiple chips on the same 3-wire bus with separate chip select lines
■ Self-timed programming cycle
■ Simultaneous programming of 1 to 32 bytes at a time
■ Status register can be polled during programming to monitor READY/BUSY
■ Write Protect (WP) pin and write disable instruction for both hardware and software write protection
■ Block write protect feature to protect against accidental writes
■ Endurance: 1,000,000 data changes
■ Data retention greater than 40 years
■ Packages available: 8-pin DIP or 8-Pin SO