The DS1211 Nonvolatile Controller x8 Chip performs five circuit functions required to render standard CMOS RAM nonvolatile:
Monitor Vcc using a precise comparator that detects power-fail and inhibits chip-enable
Monitor battery status and warn the processor of low status
Switch power between a battery and Vcc, whichever is greater
Provide for automatically switching between two batteries Power-fail detection occurs in the range of 4.75V to 4.5V with the tolerance Pin 3 grounded. If Pin 3 in connected to Vcco, then power-fail detection occurs in the range of 4.5 volts to 4.25 volts.
By combining the DS1211 nonvolatile controller/decoder chip and lithium batteries, nonvolatile RAM operation can be achieved for up to eight CMOS memories.