8

Detailed Description

The DS3231M is a serial real-time clock (RTC) driven by

an internal, temperature-compensated, microelectrome-

chanical systems (MEMS) resonator. The oscillator pro-

vides a stable and accurate reference clock and main-

tains the RTC to within Q0.432 seconds-per-day accu-

racy from -40NC to +85NC. The RTC is a low-power clock/

calendar with two programmable time-of-day alarms. INT/

SQW provides either an interrupt signal due to alarm

conditions or a 1Hz square wave. The clock/calendar

provides seconds, minutes, hours, day, date, month,

and year information. The date at the end of the month

is automatically adjusted for months with fewer than

31 days, including corrections for leap year. The clock

operates in either the 24-hour or 12-hour format with an

AM/PM indicator. The internal registers are accessible

ed voltage reference and comparator circuit monitors the

switch to the backup supply when necessary. The RST

pin provides an external pushbutton function and acts as

an indicator of a power-fail event.

Operation

The Block Diagram shows the device’s main elements.

Each of the major blocks is described separately in the

following sections.

Block Diagram

Pin Description (continued)

DS3231M

N

N

TIME-BASE

RESONATOR

TEMP

SENSOR

INTERRUPT

OR 1Hz

SELECT

DIVIDER

INT/SQW

1Hz

DIGITAL

ADJUSTMENT

FACTORY TRIM

N

32KHZ

SDA

GND

SCL

RST

CLOCK/CALENDAR

WITH ALARM

CONTROL AND STATUS

REGISTERS

INTERFACE

POWER

CONTROL

PIN

NAME

FUNCTION

8 SO

16 SO

7

15

SDA

pin requires an external pullup resistor. The pullup voltage can be up to 5.5V, regardless of the volt-

8

16

SCL

data movement on the serial interface. The pullup voltage can be up to 5.5V, regardless of the