3

AT24C128/256

0670S–SEEPR–5/06

Pin Description

SERIAL CLOCK (SCL): The SCL input is used to positive edge clock data into each

EEPROM device and negative edge clock data out of each device.

SERIAL DATA (SDA): The SDA pin is bidirectional for serial data transfer. This pin is open-

drain driven and may be wire-ORed with any number of other open-drain or open collector

devices.

DEVICE/ADDRESSES (A1, A0): The A1 and A0 pins are device address inputs that are hard-

wired or left not connected for hardware compatibility with other AT24CXX devices. When the

pins are hardwired, as many as four 128K/256K devices may be addressed on a single bus

system (device addressing is discussed in detail under the Device Addressing section). If the

pins are left floating, the A1 and A0 pins will be internally pulled down to GND if the capacitive

coupling to the circuit board V

necting the address pins to GND.

WRITE PROTECT (WP): The write protect input, when connected to GND, allows normal write

operations. When WP is connected high to V

ited. If the pin is left floating, the WP pin will be internally pulled down to GND if the capacitive

coupling to the circuit board V

necting the pin to GND.

Memory

Organization

AT24C128/256, 128K/256K SERIAL EEPROM: The 128K/256K is internally organized as

256/512 pages of 64-bytes each. Random word addressing requires a 14/15-bit data word

address.