AT21CS11 1Kb Serial EEPROM Microchip Technology AT21CS11 1Kb Serial EEPROM is a 2-pin memory (SI/O signal and Ground) that harvests energy from the signal pin to power an integrated circuit for use in consumer and industrial applications. The AT21CS11 utilizes the Single-Wire bus and only two pins are needed to access the device: SI/O and GND. The SI/O signal is a combination of data and power lines, providing power to the device with a parasitic power scheme.