21.5.5 RTC Internal Free-Running Counter Error Checking

To improve the reliability and security of the RTC, a permanent check is performed on the internal free-running counters to report non-BCD or invalid date/time values.

An error is reported by RTC_SR.TDERR if an incorrect value has been detected. The flag can be cleared by setting the RTC_SCCR.TDERRCLR.

In all cases, RTC_SR.TDERR is set again if the source of the error has not been cleared before clearing RTC_SR.TDERR. The clearing of the source of such error can be done by reprogramming a correct value on RTC_CALR and/or RTC_TIMR.

The RTC internal free-running counters may automatically clear the source of RTC_SR.TDERR due to their roll-over (i.e., every 10 seconds for SECONDS[3:0] in RTC_TIMR). In this case, RTC_SR.TDERR is held high until a clear command is asserted by writing a 1 in RTC_SCCR.TDERRCLR.