The Microchip Technology Inc. 24LC21A is a 128 x 8-bitdual-mode Electrically Erasable PROM. This device isdesigned for use in applications requiring storage andserial transmission of configuration and control information.Two modes of operation have been implemented:Transmit-Only mode and Bidirectional mode. Uponpower-up, the device will be in the Transmit-Only mode,sending a serial bit stream of the memory array from 00hto 7Fh, clocked by the VCLK pin. A valid high-to-lowtransition on the SCL pin will cause the device to enterthe transition mode, and look for a valid control byte onthe I2C™Compatible bus. If it detects a valid control byte from themaster, it will switch into Bidirectional mode, with byteselectable read/write capability of the memory arrayusing SCL. If no control byte is received, the device willrevert to the Transmit-Only mode after it receives 128consecutive VCLK pulses while the SCL pin is idle. The24LC21A is available in a standard 8-pin PDIP andSOIC package in industrial temperature range.

   Single Supply with Operation Down to 2.5V

   Completely Implements DDC1™/DDC2™Interface for Monitor Identification, IncludingRecovery to DDC1

   Pin and Function Compatible with 24LC21

   Low-Power CMOS Technology

   2-Wire Serial Interface Bus, I2C™ Compatible

   100 kHz (2.5V) and 400 kHz (5V) Compatibility

   Self-Timed Write Cycle (including auto-erase)

   Page Write Buffer for up to Eight Bytes

   1,000,000 Erase/Write Cycles Ensured

   Data Retention > 200 years