MC68HC908LJ24 Datasheet, PDF (223/464 Pages) Motorola, Inc – Microcontrollers

Freescale Semiconductor, Inc.
Real Time Clock (RTC)
Functional Description
12.5.1 Time Functions
Real time clock functions are provided by the second, minute, and hour
counter registers. All three clock counters are able to generate interrupts
on every counter increment, providing periodic interrupts for the second
(SECF), minute (MINF), and hour (HRF). A CPU interrupt request is
generated if the corresponding enable bit (SECIE, MINIE, and HRIE) is
also set.
12.5.2 Calendar Functions
Calendar functions are provided by the day, day-of-week, month, and
year counter registers. The roll over of the day counter is automatically
adjusted for the month and leap years. The setting for the year counter
ranges from 1901 to 2099.
The day flag (DAYF) is set on every increment of the day counter. A CPU
interrupt request is generated if the day interrupt enable bit (DAYIE) is
also set.
12.5.3 Alarm Functions
An alarm function is provided for the minute and hour counters. When
minute counter matches the value stored in the alarm minute register,
and the hour counter matches the value stored in the alarm hour register,
the alarm flag (ALMF) will be set. A CPU interrupt request is generated
if the alarm interrupt enable bit (ALMIE) is also set.
12.5.4 Chronograph Functions
The chronograph function is provided by a counter clocked at 128Hz
(CGMXCLK/256). This counter can be started, stopped, and cleared at
any time. The value of this chronograph counter is converted to 100Hz
resolution and stored in the chronograph data register. Hence, the value
in the chronograph register counts from 0 to 99 (and rolls over), with
each increment representing 1/100th of a second (10ms).
MC68HC908LJ24/LK24 — Rev. 2
MOTOROLA
Real Time Clock (RTC)
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Data Sheet
223