Description
The AT24C21 provides 1024 bits of serial electrically erasable and programmable read only memory (EEPROM) organized as 128 words of 8 bits each. The device is optimized for use in applications requiring data storage and serial transmission of configuration and control information. The AT24C21 features two modes of operation: Transmit-Only Mode and Bidirectional Mode. Upon power-up, the AT24C21 will be in the Transmit-Only Mode, sending a serial-bit stream of the entire memory contents, clocked via the VCLK pin. The Bidirectional Mode is selected by a valid high-to-low transition on the SCL pin and offers byte selectable read/write capability of the entire memory array. The AT24C21 is available in space saving 8-pin PDIP and 8-pin SOIC packages.

FEATUREs
• 2-Wire Serial Interface
• Schmitt Trigger, Filtered Inputs For Noise Suppression
• DDC1™/ DDC2™ Interface Compliant for Monitor Identification
• Low Voltage Operation
   – 2.5 (VCC = 2.5V to 5.5V)
• Internally Organized 128 x 8
• 100 kHz (2.5V) Compatibility
• 8-Byte Page Write Mode
• Write Protection Available
• Self-timed Write Cycle (10 ms max)
• High Reliability
   – Endurance: 1 Million Write Cycles
   – Data Retention: 100 Years
   – ESD Protection: >3000V
• 8-Pin PDIP and JEDEC SOIC Packages