The DS1243Y 64K NV SRAM with Phantom Clock is a fully static nonvolatile RAM (organized as 8192 words by 8 bits) with a builtin real time clock. The DS1243Y has a selfcontained lithium energy source and control circuitry which constantly monitors VCC for an outoftolerance condition. When such a condition occurs, the lithium energy source is automatically switched on and write protection is unconditionally enabled to prevent corrupted data in both the memory and real time clock.