The AT28HC256 is a high-performance electrically erasable and programmable readonly memory. Its 256K of memory is organized as 32，768 words by 8 bits. Manufactured with Atmel’s advanced nonvolatile CMOS technology， the AT28HC256 offers access times to 70 ns with power dissipation of just 440 mW. When the AT28HC256 is deselected， the standby current is less than 5 mA. The AT28HC256 is accessed like a Static RAM for the read or write cycle without the need for external components. The device contains a 64-byte page register to allow writing of up to 64 bytes simultaneously. During a write cycle， the address and 1 to 64 bytes of data are internally latched， freeing the addresses and data bus for other operations. Following the initiation of a write cycle， the device will automatically write the latched data using an internal control timer. The end of a write cycle can be detected by DATA Polling of I/O7. Once the end of a write cycle has been detected a new access for a read or write can begin. Atmel’s 28HC256 has additional features to ensure high quality and manufacturability. The device utilizes internal error correction for extended endurance and improved data retention characteristics. An optional software data protection mechanism is available to guard against inadvertent writes. The device also includes an extra 64 bytes of EEPROM for device identification or tracking.