The IS24C128A/256A is an electrically erasable PROM device that uses the standard 2-wire interface for communications. The IS24C128A is 128K-bit (16Kx8) and the IS24C256A is 256K-bit (32Kx8). These EEPROM are offered in a wide operating voltage range of 1.8V to 5.5V to be compatible with most application voltages. ISSI designed the IS24C128A/256A to be an efficient 2-wire EEPROM solution. The devices are packaged in 8-pin PDIP, 8-pin (JEDEC) SOIC, and 8pin (EIAJ) SOIC. The IS24C128A/256A maintains compatibility with the popular 2-wire bus protocol, so it is easy to design into applications implementing this bus type. The simple bus consists of the Serial Clock wire (SCL) and the Serial Data wire (SDA). Using the bus, a Master device such as a microcontroller is usually connected to one or more Slave devices such as the IS24C128A/256A. The bit stream over the SDA line includes a series of bytes, which identifies a particular Slave device, an instruction, an address within that Slave device, and a series of data, if appropriate. The IS24C128A/256A has a Write Protect pin (WP) to allow blocking of any write instruction transmitted over the bus.