RTC/TCXO/Crystal

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11

Figure 1. 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

AM/PM

02h

0

12/

24

10 Hour

10 Hour

Hour

Hours

1–12 +

AM/PM

00–23

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

AM/PM

09h

A1M3

12/

24

10 Hour

10 Hour

Hour

Alarm 1 Hours

1–12 +

AM/PM

00–23

Day

Alarm 1 Day

1–7

0Ah

A1M4

DY/

DT

10 Date

Date

Alarm 1 Date

1–31

0Bh

A2M2

10 Minutes

Minutes

Alarm 2 Minutes

00–59

AM/PM

0Ch

A2M3

12/

24

10 Hour

10 Hour

Hour

Alarm 2 Hours

1–12 +

AM/PM

00–23

Day

Alarm 2 Day

1–7

0Dh

A2M4

DY/

DT

10 Date

Date

Alarm 2 Date

1–31

0Eh

EOSC

BBSQW

CONV

RS2

RS1

INTCN

A2IE

A1IE

Control

—

0Fh

OSF

0

0

0

EN32kHz

BSY

A2F

A1F

Control/Status

—

10h

SIGN

DATA

DATA

DATA

DATA

DATA

DATA

DATA

Aging Offset

—

11h

SIGN

DATA

DATA

DATA

DATA

DATA

DATA

DATA

MSB of Temp

—

12h

DATA

DATA

0

0

0

0

0

0

LSB of Temp

—

Address Map

Figure 1 shows the address map for the DS3231 time-

keeping registers. During a multibyte access, when the

address pointer reaches the end of the register space

START or address pointer incrementing to location 00h,

the current time is transferred to a second set of regis-

ters. The time information is read from these secondary

registers, while the clock may continue to run. This

eliminates the need to reread the registers in case the

main registers update during a read.

event, it is possible that the microcontroller and

chronized, e.g., the microcontroller resets while read-

ing data from the DS3231. When the microcontroller

known state by toggling SCL until SDA is observed to

be at a high level. At that point the microcontroller

should pull SDA low while SCL is high, generating a

START condition.

Clock and Calendar

The time and calendar information is obtained by read-

ing the appropriate register bytes. Figure 1 illustrates

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