Analog Devices ADSP-SC58 Series Hardware Reference Manual page 1120

RTC Architectural Concepts
The key use of the RTC is to provide the time keeping function and maintain the time and date in an accurate and
reliable manner with minimal power consumption. In addition to time keeping it also provides the stopwatch and
alarm features. The RTC uses the internal counters to keep the time of the day in terms of seconds, minutes, hours
and days. This data is enough for the user application to extract the date and time information from the RTC.
Interrupts can be issued periodically, either every second, every minute, every hour, or every day. Each of these inter-
rupts can be independently controlled. It is the responsibility of the program to set the correct time by a software
write into the RTC_CLK
RTC provides two alarm features, programmed with the RTC alarm register (RTC_ALM). The first is a time of day
alarm (hour, minute, and second). When the alarm interrupt is enabled, the RTC generates an interrupt each day at
the time specified. The second alarm feature allows the application to specify a day as well as a time.
The RTC also provides a stopwatch function that acts as a countdown timer. The application can program a second
count into the RTC stopwatch count register (RTC_STPWTCH). When the stopwatch interrupt is enabled and the
specified number of seconds has elapsed, the RTC generates an interrupt.
RTC Block Diagram
The RTC block diagram provides a top level block diagram of the elements used. The main blocks of the RTC are
the individual counters, the alarm register, and the event control.
Figure 22-1: RTC Block Diagram
Power Supply Partitioning
The RTC logic is partitioned between the processor core supply voltage and RTC supply voltage. The core of RTC
unit functions on a RTC power supply so that the RTC can maintain the time even if the processor power is off.
When the core supply voltage is absent, interrupts are ignored.
22–4
register. Once set, the counters maintain time as long as the RTC supply is valid. The
24 HOURS HOURS
EVENT EVENT
DAYS HOURS
COUNTER COUNTER
9
5
Y Y Y
EQUAL? EQUAL?
9 5
RTC_ALARM REGISTER
STOPWATCH
DAY
ALARM
EVENT
ALARM
EVENT
ADSP-SC58x/ADSP-2158x SHARC+ Processor Hardware Reference
MINUTES SECONDS
EVENT EVENT
1 TICK
MINUTES SECONDS
COUNTER COUNTER
6 6
Y
EQUAL? EQUAL?
6
6
STOPWATCH
ENABLE
COUNTER
16
Y
EQUAL 0?
STOPWATCH
EVENT
PRESCALE
COUNTER
RTXI
32.768 kHz
WRITE
RTC_STPWTCH
SET
RST