1

Features

– Endurance: 1 Million Write Cycles

– Data Retention: 100 Years

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 con-

figuration 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-lead PDIP and 8-lead

JEDEC SOIC packages.

2-wire Serial

EEPROM

1K (128 x 8)

AT24C21

Not Recommended

for New Designs

Rev. 0405I–SEEPR–7/03

2-Wire, 1K

Serial EEPROM

Pin Configurations

Pin Name

Function

NC

No Connect

SDA

Serial Data

SCL

Serial Clock Input

(Bidirectional Mode)

VCLK

Serial Clock Input

(Transmit-only Mode)

8-lead PDIP

1

2

3

4

8

7

6

5

NC

NC

NC

GNE

VCC

VCLK

SCL

SDA

8-lead SOIC

1

2

3

4

8

7

6

5

NC

NC

NC

GND

VCC

VCLK

SCL

SDA