RTC_SHIFTR register
| SUBFS | Subtract a fraction of a second These bits are write only and is always read as zero. Writing to this bit has no effect when a shift operation is pending (when SHPF=1, in RTC_ISR). The value which is written to SUBFS is added to the synchronous prescaler’s counter. Since this counter counts down, this operation effectively subtracts from (delays) the clock by: Delay (seconds) = SUBFS / ( PREDIV_S + 1 ) A fraction of a second can effectively be added to the clock (advancing the clock) when the ADD1S function is used in conjunction with SUBFS, effectively advancing the clock by : Advance (seconds) = ( 1 - ( SUBFS / ( PREDIV_S + 1 ) ) ) . |
| ADD1S | Add one second 0: No effect 1: Add one second to the clock/calendar This bit is write only and is always read as zero. Writing to this bit has no effect when a shift operation is pending (when SHPF=1, in RTC_ISR). This function is intended to be used with SUBFS (see description below) in order to effectively add a fraction of a second to the clock in an atomic operation. |