Maxim Integrated MAX32600, User Manual, Page: 585 / 687

MAX32600 User’s Guide System Clock, Timers/Counters, Watchdog Timers and Real Time Clock 10.3 Real Time Clock (RTC)
• The RTCTMR_CTRL.pending status bit will change to 1 to indicate that clock domain synchronization is pending; the bit will change back to 0 once the
synchronization has completed.
Determining the Proper RTC Timer Prescale Value
The RTC timer register is always a fixed 32-bits in length; the input to the RTC block is always a fixed 4kHz frequency derived from the output of the 32kHz external
crystal oscillator. However, by using the prescaler, it is possible to change the rate at which the RTC timer increments, effectively determining the unit of time assigned
to the RTC timer LSB.
As shown in the table below, the assigned prescale value determines the number of 4kHz clock ticks that are needed in order to increment the main RTC timer
register by one.
PRESCALE Prescale Reload 4kHz ticks in LSB Min Timer Value (s) Max Timer Value (s) Max Timer Value in Days Max Timer Value in Years
0h 000h 1 0.00024 1048576 12 0.0
1h 001h 2 0.00049 2097152 24 0.1
2h 003h 4 0.00098 4194304 49 0.1
3h 007h 8 0.00195 8388608 97 0.3
4h 00Fh 16 0.00391 16777216 194 0.5
5h 01Fh 32 0.00781 33554432 388 1.1
6h 03Fh 64 0.01563 67108864 777 2.2
7h 07Fh 128 0.03125 134217728 1553 4.4
8h 0FFh 256 0.06250 268435456 3107 8.7
9h 1FFh 512 0.12500 536870912 6214 17.5
Ah 3FFh 1024 0.25000 1073741824 12428 34.9
Bh 7FFh 2048 0.50000 2147483648 24855 69.8
Ch FFFh 4096 1.00000 4294967296 49710 139.6
For each RTCTMR_PRESCALE setting, the Prescale Reload indicates the reload value that will be loaded to the RTC’s internal 12-bit prescaler counter when the
RTC timer is first started or when the prescaler counter reaches zero. On each 4kHz tick, the prescaler counter will either be reset with the reload value (if the
prescaler counter equals zero) or it will be decremented by one (if the prescaler counter is nonzero). Each time the prescaler counter ’rolls under’ at zero and is
reloaded, the main RTC timer will be incremented by one.
Rev.1.3 April 2015 Maxim Integrated Page 567