The DS1225AB and DS1225AD are 65,536-bit, fully static, nonvolatile (NV) SRAMs organized as 8192 words by 8 bits. Each NV SRAM has a self-contained lithium energy source and control circuitry which constantly monitors VCCfor an out-of-tolerance condition. When such a condition occurs, the lithium energy source is automatically switched on and write protection is unconditionally enabled to prevent data corruption. The NV SRAMs can be used in place of existing 8k x 8 SRAMs directly conforming to the popular bytewide 28-pin DIP standard. The devices also match the pinout of the 2764 EPROM and the 2864 EEPROM, allowing direct substitution while enhancing performance. There is no limit on the number of write cycles that can be executed and no additional support circuitry is required for microprocessor interfacing.