The CAT25C128/256 is a 128K/256K-Bit SPI Serial CMOS EEPROM internally organized as 16Kx8/32Kx8 bits. Catalyst's advanced CMOS Technology substantially reduces device power requirements. The CAT25C128/256 features a 64-byte page write buffer. The device operates via the SPI bus serial interface and is enabled through a Chip Select (CS). In addition to the Chip Select, the clock input (SCK), data in (SI) and data out (SO) are required to access the device.