11

Clock and Calendar

The time and calendar information is obtained by read-

ing the appropriate register bytes. Table 2 shows the

RTC registers. The time and calendar data are set or

initialized by writing the appropriate register bytes. The

contents of the time and calendar registers are in the

binary-coded decimal (BCD) format. The device can

be run in either 12-hour or 24-hour mode. Bit 6 of the

Hours register is defined as the 12-hour or 24-hour mode

select bit. When high, the 12-hour mode is selected. In

the 12-hour mode, bit 5 is the AM/PM bit with logic-high

being PM. In the 24-hour mode, bit 5 is the 20-hour bit

(20–23 hours). The century bit (bit 7 of the Month regis-

ter) is toggled when the Years register overflows from 99

Table 2. Timekeeping Registers

Note: Unless otherwise specified, the registers’ state is not defined when power is first applied.

ADDRESS

BIT 7

MSB

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

LSB

FUNCTION

RANGE

00h

0

10 Seconds

Seconds

Seconds

00–59

01h

0

10 Minutes

Minutes

Minutes

00–59

02h

0

12/24

AM/PM

10

Hours

Hour

Hours

1–12 +

AM/PM

00–23

20

Hours

03h

0

0

0

0

0

Day

Day

1–7

04h

0

0

10 Date

Date

Date

01–31

05h

Century

0

0

10

Month

Month

Month/Century

01–12 +

Century

06h

10 Year

Year

Year

00–99

07h

A1M1

10 Seconds

Seconds

Alarm 1

Seconds

00–59

08h

A1M2

10 Minutes

Minutes

Alarm 1

Minutes

00–59

09h

A1M3

12/24

AM/PM

10

Hours

Hour

Alarm 1 Hours

1–12 +

AM/PM

00–23

20

Hours

0Ah

A1M4

DY/DT

10 Date

Day

Alarm 1 Day

1–7

Date

Alarm 1 Date

1–31

0Bh

A2M2

10 Minutes

Minutes

Alarm 2

Minutes

00–59

0Ch

A2M3

12/24

AM/PM

10

Hours

Hour

Alarm 2 Hours

1–12 +

AM/PM

00–23

20

Hours

0Dh

A2M4

DY/DT

10 Date

Day

Alarm 2 Day

1–7

Date

Alarm 2 Date

1–31

0Eh

EOSC

BBSQW

CONV

NA

NA

INTCN

A2IE

A1IE

Control

—

0Fh

OSF

0

0

0

EN32KHZ

BSY

A2F

A1F

Status

—

10h

SIGN

DATA

DATA

DATA

DATA

DATA

DATA

DATA

Aging Offset

—

11h

SIGN

DATA

DATA

DATA

DATA

DATA

DATA

DATA

Temperature

MSB

—

12h

DATA

DATA

0

0

0

0

0

0

Temperature

LSB

—