22.5.5 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 bit in the status register if an incorrect value has been detected. The flag can be cleared by setting RTC_SCCR.TDERRCLR.

In all cases, the RTC_SR.TDERR error flag will be set again if the source of the error has not been cleared before clearing the RTC_SR.TDERR flag. The clearing of the source of such an error can be done by reprogramming a correct value in 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 RTC_TIMR.SECONDS[3:0] field). In this case the RTC_SR.TDERR is held high until a clear command is asserted by RTC_SCCR.TDERRCLR.