Datasheet

ADSP-21479 EZ-Board Evaluation System Manual 1-13
Using ADSP-21479 EZ-Board
Be default, the watch timer interface is turned off. In order to use the fea-
ture, a user needs to turn switch
SW13 position 8 ON. SW13 connects the
watch dog reset out pin to the ADM708 system reset circuit. See “External
Port Enable Switch (SW13)” on page 2-12. Special attention must be paid
to this function because it can cause the processor and EZ-Board to
remain in a permanent reset.
Example programs are included in the EZ-Board installation directory to
demonstrate watch dog timer functionality.
Real-Time Clock Interface
The real-time clock (RTC) of the ADSP-21479 processor provides a
robust set of digital watch features, including current time, stopwatch, and
alarm. The RTC is clocked by a 32.768 kHz crystal external to the proces-
sor. The RTC peripheral has dedicated power supply pins so that it can
remain powered up and clocked even when the rest of the processor is in a
low power state. The RTC provides several programmable interrupt
options, including interrupt per second, minute, hour, or day clock ticks,
interrupt on programmable stopwatch countdown, or interrupt at a pro-
grammed alarm time. An RTCLKOUT signal that operates at 1 Hz is also
provided for calibration.
The 32.768 kHz input clock frequency is divided down to a 1 Hz signal
by a prescaler. The counter function of the timer consists of four counters:
a 60-second counter, a 60-minute counter, a 24-hour counter, and an
32,768-day counter. When the alarm interrupt is enabled, the alarm func-
tion generates an interrupt when the output of the timer matches the
programmed value in the alarm control register. There are two alarms:
The first alarm is for a time of day. The second alarm is for a day and time
of that day.
The stopwatch function counts down from a programmed value, with
one-second resolution. When the stopwatch interrupt is enabled and the
counter underflows, an interrupt is generated.