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DS1308

Functional Diagram

Detailed Description

The DS1308 serial RTC is a low-power, full BCD clock/

calendar plus 56 bytes of NV SRAM. Address and data

clock/calendar provides seconds, minutes, hours, day,

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

date 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 DS1308 has a built-in power-sense

circuit that detects power failures and automatically

Operation

The DS1308 operates as a slave device on the serial bus.

Access is obtained by implementing a START condition

and providing a device identification code, followed by

data. Subsequent registers can be accessed sequen-

tially until a STOP condition is executed. The device is

fully accessible and data can be written and read when

oscillator and timekeeping functions are maintained

Diagram shows the main elements of the DS1308.

An enable bit in the seconds register (CH) controls the

oscillator. Oscillator startup times are highly dependent

upon crystal characteristics, PCB leakage, and layout.

High ESR and excessive capacitive loads are the major

contributors to long startup times. A circuit using a crystal

with the recommended characteristics and proper layout

usually starts within 1 second.

On the first application of power to the device, the time

and date registers are reset to 01/01/00 01 00:00:00 (DD/

MM/YY DOW HH:MM:SS), and CH bit in the seconds

register is set to 0.

DS1308

N

N

/4

/32

EXTSYNC

CONTROL LOGIC

OSC-1Hz

POWER CONTROL

RAM

CLOCK AND

CALENDAR REGISTERS

/2

128Hz

OSC-1Hz

SQW/CLKIN

X1

X2

SCL

SDA

4.096kHz

8.192kHz

32.768kHz

MUX/

BUFFER

DIVIDER

EXT-1Hz

SERIAL BUS

INTERFACE AND

ADDRESS

REGISTER