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The three time alarm bytes can be used in two ways. First, when the alarm time is written in the

appropriate hours, minutes, and seconds alarm locations, the alarm interrupt is initiated at the specified

time each day if the alarm enable bit is high. The second use condition is to insert a “don’t care” state in

one or more of the three time alarm bytes. The “don’t care” code is any hexadecimal value from C0 to

FF. The two most significant bits of each byte set the “don’t care” condition when at logic 1. An alarm is

generated each hour when the “don’t care” bits are set in the hours byte. Similarly, an alarm is generated

every minute with “don’t care” codes in the hours and minute alarm bytes. The “don’t care” codes in all

three time alarm bytes create an interrupt every second. The three time-alarm bytes can be used with the

date alarm as described in Wake-Up/Kickstart. The century counter is discussed later in this text.

Table 1. TIME, CALENDAR, AND ALARM DATA MODES

RANGE

ADDRESS

LOCATION

FUNCTION

DECIMAL

RANGE

BINARY DATA MODE

BCD DATA MODE

OOH

Seconds

0 to 59

00 to B

00 to 59

01H

Seconds Alarm

0 to 59

00 to 3B

00 to 59

02H

Minutes

0 to 59

00 to 3B

00 to 59

03H

Minutes Alarm

0 to 59

00 to 3B

00 to 59

Hours 12-hour Mode

1 to 12

01 to 0C AM, 81 to 8C PM

01 to 12 AM, 81 to 92 PM

04H

Hours 24-hour Mode

0 to 23

00 to 17

00 to 23

Hours Alarm 12-hour Mode

1 to 12

01 to 0C AM, 81 to 8C PM

01 to 12 AM, 81 to 92 PM

05H

Hours Alarm 24-hour Mode

0 to 23

00 to 17

00 to 23

06H

Days of the Week Sunday = 1

1 to 7

01 to 07

01 to 07

07H

Date of Month

1 to 31

01 to 1F

01 to 31

08H

Month

1 to 12

01 to 0C

01 to 12

09H

Year

0 to 99

00 to 63

00 to 99

BANK 1, 48H

Century

0 to 99

00 to 63

00 to 99

BANK 1, 49H

Date Alarm

1 to 31

01 to 1F

01 to 31