3

5296A–SEEPR–1/08

AT24C128B

4.

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/PAGE ADDRESSES (A2, A1, A0): The A2, A1, and A0 pins are device address inputs

that are hardwired (directly to GND or to Vcc) for compatibility with other AT24Cxx devices.

When the pins are hardwired, as many as eight 128K devices may be addressed on a single bus

system. (Device addressing is discussed in detail under “Device Addressing,” page 8.) A device

is selected when a corresponding hardware and software match is true. If these pins are left

floating, the A2, A1, and A0 pins will be internally pulled down to GND. However, due to capaci-

tive coupling that may appear during customer applications, Atmel recommends always

connecting the address pins to a known state. When using a pull-up resistor, Atmel recommends

using 10k

Ω or less.

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

operations. When WP is connected directly to Vcc, all write operations to the memory are inhib-

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

capacitive coupling that may appear during customer applications, Atmel recommends always

connecting the WP pins to a known state. When using a pull-up resistor, Atmel recommends

using 10k

Ω or less.