Writes the current day number from the DN register to the RTC.

This instruction does not write the day of week on all ARM based controllers such as the EC1 and HMI430 as they automatically calculate the day of week.  Instead, executing this instruction on these controllers will load the day number based on the date in the RTC registers (not the date in the RTC).  This can be useful in your user interface, as you can display the calculated day of week while the user is adjusting the date.

RTC documentation and tutorial

Dialect exclusions: Not available in dialects before 16.