What is an clock data validation?

Real Time ClockFunction

These RTCs provide a power-on reset function, an oscillation halt sensing function and a supply voltage monitoring function.
These functions can be applied to judge a clock data validity. 

• Power-on Reset Function
  Power-on reset circuit is configured to reset a control register and store the status as a flag after initial power on from 0 V without backup battery.
• Oscillation Halt Sensing Function
  Oscillation halt sensing circuit is equipped with internal registers configured to record any past oscillation halt as a flag.
• Supply Voltage Monitoring Function
  Supply voltage monitoring circuit is configured to record a drop in supply voltage below supply voltage monitoring thresholds.