5.1 Memory Organization

The AT21CS01/AT21CS11 internal memory array is partitioned into two regions. The main 1-Kbit EEPROM is organized as 16 pages of eight bytes each. The Security register is 256 bits in length, organized as four pages of eight bytes each. The lower two pages of the Security register are read-only and have a factory‑programmed, 64‑bit serial number that is unique across all AT21CS Series serial EEPROMs. The upper two pages of the Security register are user-programmable and can be subsequently locked (see Locking the Security Register).