Overview Of Real Time Clock - Fujitsu F2MC-8FX Hardware Manual

CHAPTER 27 REAL TIME CLOCK
27.1

Overview of Real time clock

The real time clock supplies second, minute, hour, day of the week, day, month and year
information. it also features auto-calibration, automatic leap-year adjustment and alarm
interrupt function.
Function of the real time clock
The real time clock is timer counter circuit that keeps track of time with information of second, minute,
hour, day of the week, day, month and year to the system. Additionally, leap-year circuit features automatic
leap-year adjustment. Comparison circuits allow alarm interrupt function by pre-setting information of
minute, hour, day and year into the corresponding registers.
Prescaler is incorporated so as to generate one-second ticks to the real time clock. In case there is deviation
from one-second due to the discrepancy induced by the oscillator. Prescaler fine tuning circuit is provided
to perform fine-tuning. Apart from 1Hz, Prescaler can output 0.1Hz, 64Hz and 1024Hz as well. Through
the output pin, this set of frequencies works as test clocks.
The Real time clock have two different calibraion methods: Manual calibraion and Auto-calibration.
Manual calibration, which is to calibrate by using test clocks and fine-tune RTC's tick-time by setting
appropriate value in the frequency fine-tuning register.
Auto-calibration function is used to correct the clock error by loading the difference which is measurd by
the frequency (32.768KHz) of subclock automatically with an known precise external 1Hz reference input
(CALPL) into the Frequency Fine-Tuning Register (FFTR) automatically.
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