AT25x SPI Serial EEPROMs Microchip Technology AT25x SPI Serial EEPROMs are designed for use in applications where low-power and low-voltage operations are essential. These EEPROMs feature block write protection, 20MHz clock cycle, self-timed write cycle, write protect pin, and write disable instructions. The AT25x EEPROMs are enabled through the Chip Select pin (CS) and accessed via a 3-wire interface. This 3-wire interface consists of Serial Clock (SCK), Serial Data Input (SI), and Serial Data Output (SO).