The DS1258 128k x 16 nonvolatile (NV) SRAMs are 2,097,152-bit fully static, NV SRAMs, organized as 131,072 words by 16 bits. Each NV SRAM has a self-contained lithium energy source and control circuitry that constantly monitors VCC for 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. DIP-package DS1258 devices can be used in place of solutions that build NV 128k x 16 memory by utilizing a variety of discrete components. There is no limit on the number of write cycles that can be executed and no additional support circuitry is required for microprocessor interfacing.