The DS1218 Nonvolatile Controller Chip supplies circuitry required to render standard CMOS RAM nonvolatile. VCC is monitored using a precise comparator that detects power-fail and inhibits chip-enable holding a write-protect status until power supplies return to nominal levels. The DS1218 switches active power supplies between VCC and a battery source, whichever is greater. The switch has a voltage drop of less than 0.2V. * Converts CMOS RAM into nonvolatile memories * Unconditionally write protects when VCC is out of tolerance * Automatically switches to battery when power fail occurs * Space saving 8-pin PDIP or 8-pin 150 mil SO Packages * Consumes less than 100nA of battery current