Alarm; Sampling Timer; Minute Stopwatch; Table 23-1 Sampling Timer Frequencies - Motorola DragonBall MC9328MX1 Reference Manual

23.1.2 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.
If the alarm is not disabled, it will reoccur every 512 days. If a single alarm
is desired, the alarm function must be disabled through the RTC Interrupt
Enable register (RTCIENR).

23.1.3 Sampling Timer

The sampling timer is designed to support application software. The sampling timer generates a periodic
interrupt with the frequency specified by the SAMx bits of the RTCIENR register. This timer can be used
for digitizer sampling, keyboard debouncing, or communication polling. The sampling timer operates only
if the real-time clock is enabled. Table 23-1 lists the interrupt frequencies of the sampling timer for the
possible reference clocks.
Multiple SAMx bits may be set in the RTC Interrupt Enable Register (RTCIENR). The corresponding bits
in the RTC Interrupt Status Register (RTCISR) will be set at the noted frequencies.
Sampling
Frequency
SAM7
SAM6
SAM5
SAM4
SAM3
SAM2
SAM1
SAM0

23.1.4 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—for example, to turn off the LCD controller after five minutes of
inactivity, program a value of 0x04 into the Stopwatch Count (CNT) field of the Stopwatch Minutes
(STPWCH) register (see Table 23-12 on page 23-15 for a complete list of settings for the STPWCH
register). 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. Note that the actual
delay includes the seconds from setting the stopwatch to the next minute tick.
MOTOROLA
NOTE:
Table 23-1. Sampling Timer Frequencies
32.768 kHz
Reference Clock Reference Clock
512 Hz
256 Hz
128 Hz
64 Hz
32 Hz
16 Hz
8 Hz
4 Hz
Real-Time Clock (RTC)
32 kHz
Reference Clock
500 Hz
250 Hz
125 Hz
62.5 Hz
31.25 Hz
15.625 Hz
7.8125 Hz
3.90625 Hz 4.6875 Hz
Operation
38.4 kHz
600 Hz
300 Hz
150 Hz
75 Hz
37.5 Hz
18.75 Hz
9.375 Hz
23-3