Real-Time Clock
MCF52110 ColdFire® Integrated Microcontroller Reference Manual, Rev. 1
11-14
Freescale Semiconductor
Preliminary
Interrupts signal when each of the four counters increments, and can be used to indicate when a counter
rolls over. For example, each tick of the seconds counter causes the 1HZ interrupt flag to be set. When the
seconds counter rolls from 59 to 00, the minute counter increments and the MIN interrupt flag is set. The
same is true for the minute counter with the HR signal, and the hour counter with the DAY signal.
11.3.2
Alarm
There are three alarm registers that mirror the three counter registers. An alarm is set by accessing the
real-time clock alarm registers (ALRM_HM, ALRM_SEC, and DAYALARM) and loading the exact time
that the alarm should generate an interrupt. When the TOD clock value and the alarm value coincide, if the
ALM bit in the real-time clock interrupt enable register (RTCIENR) is set, an interrupt occurs. Please be
noted that if the alarm is not disabled, it reoccurs every 65536 days. If a single alarm is desired, the alarm
function must be disabled through the RTC Interrupt Enable Register (RTCIENR).
11.3.3
Minute Stopwatch
The minute stopwatch performs a countdown with a one minute resolution. It can be used to generate an
interrupt on a minute boundary. At each minute, the value in the stopwatch is decremented. When the
stopwatch value reaches -1, the interrupt occurs. The value of the register does not change until it is
reprogrammed. The actual delay includes the seconds from setting the stopwatch to the next minute tick.
11.4
Initialization/Application Information
11.4.1
Flow Chart of RTC Operation
shows the flow chart of a typical RTC operation.
