The AT25010/020/040 provides 1024/2048/4096 bits of serial electrically erasable programmable read only memory (EEPROM) organized as 128/256/512 words of 8 bits each. The device is optimized for use in many industrial and commercial applications where low power and low voltage operation are essential. The AT25010/020/040 is available in space saving 8-pin PDIP and 8-pin JEDEC (SOIC) packages. The AT25010/020/040 is enabled through the Chip Select pin (CS ) and accessed via a 3-wire interface consisting of Serial Data Input (SI), Serial Data Output (SO), and Serial Clock (SCK). All programming cycles are completely self-timed, and no separate ERASE cycle is required before WRITE. BLOCK WRITE protection is enabled by programming the status register with one of four blocks of write protection. Separate program enable and program disable instructions are provided for additional data protection. Hardware data protection is provided via the WP pin to protect against inadvertent write attempts. The HOLD pin may be used to suspend any serial communication without resetting the serial sequence.