MC68HC908LJ24 Datasheet, PDF (221/464 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Real Time Clock (RTC)
Functional Description
12.5 Functional Description
The RTC module provides clock indications in seconds, minutes, and
hours; calendar indications in day-of-week, day-of-month, month, and
year; with automatic adjustment for month and leap year. Reading the
clock and calendar registers return the current time and date. Writing to
these registers set the time and date, and the counters will continue to
count from the new settings.
The alarm interrupt is set for the hour and minute. When the hour and
minute counters matches the time set in the alarm hour and minute
registers, the alarm flag is set. The alarm can be configured to generate
a CPU interrupt request.
A 1/100 seconds chronograph counter is provided for timing
applications. This counter can be independently enabled or disabled,
and cleared at any time.
RTC module interrupts include the alarm interrupt and seven periodic
interrupts from the clock and chronograph counters.
A frequency compensation mechanism is built into this RTC module to
allow adjustments made to the RTC clock when a less accurate
32.768kHz crystal is used.
The 1-Hz clock that drives the clock and calendar could make use of the
built-in compensation mechanism for crystal frequency error
compensation so that the 1-Hz clock could be made more accurate than
the frequency accuracy of the crystal that drive the module. The
compensation value can be provided by application software or acquire
automatically during calibration operation of the module.
Figure 12-2 shows the structure of the RTC module.
MC68HC908LJ24/LK24 — Rev. 2
MOTOROLA
Real Time Clock (RTC)
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Data Sheet
221