SH7721 datasheet(644/1524 Pages) RENESAS

644 / 1524 page

Section 17 Realtime Clock (RTC)

Rev. 3.00 Jan. 18, 2008 Page 582 of 1458

REJ09B0033-0300

17.4.4

Alarm Function

Figure 17.4 shows how to use the alarm function.

Write 0 to AIE in RCR1

to prevent errorneous interrupt

Clock running

Set alarm time

Disable alarm

interrupt

Always clear, since the flag may have been

set while the alarm time was being set.

Write 1 to AIE in RCR1

Clear alarm flag

Enable alarm

interrupt

Monitor alarm time

(wait for interrupt or

check alarm flag)

Figure 17.4 Using Alarm Function

Alarms can be generated using seconds, minutes, hours, day of the week, date, month, year, or any

combination of these. Set the ENB bit in the register on which the alarm is placed to 1, and then

set the alarm time in the lower bits. Clear the ENB bit in the register on which the alarm is not

placed to 0.

When the clock and alarm times match, 1 is set in the AF bit in RCR1. Alarm detection can be

checked by reading this bit, but normally it is done by interrupt. If 1 is set in the AIE bit in RCR1,

an interrupt is generated when an alarm occurs.

The alarm flag is set when the clock and alarm times match. However, the alarm flag can be

cleared by writing 0.

SH7721 Datasheet(PDF) 644 Page - Renesas Technology Corp