Dallas Semiconductor DS1307ZN, DS1307Z, DS1307N, DS1307 Datasheet

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DS1307

64 X 8 Serial Real Time Clock

FEATURES

 Real time clock counts seconds, minutes,

hours, date of the month, month, day of the
week, and year with leap year compensation
valid up to 2100

 56 byte nonvolatile RAM for data storage
 2-wire serial interface
 Programmable squarewave output signal
 Automatic power-fail detect and switch

circuitry

 Consumes less than 500 nA in battery backup

mode with oscillator running

 Optional industrial temperature range

-40°C to +85°C

 Available in 8-pin DIP or SOIC
 Recognized by Underwriters Laboratory

ORDERING INFORMATION

DS1307 8-Pin DIP
DS1307Z 8-Pin SOIC (150 mil)
DS1307N 8-Pin DIP (Industrial)
DS1307ZN 8-Pin SOIC (Industrial)

PIN ASSIGNMENT

l

8

V

7
6
5

8
7
6
5

CC

SQW/OUT
SCL
SDA

V

CC

SQW/OUT
SCL
SDA

X1

2

X2

V

3

BAT

GND

DS1307 8-Pin DIP (300 mil)

GND

DS1307Z 8-Pin SOIC (150 mil)

4

l

X1

2

X2

V

BAT

3
4

PIN DESCRIPTION

VCC - Primary Power Supply
X1, X2 - 32.768 kHz Crystal Connection
V

- +3V Battery Input

BAT

GND - Ground
SDA - Serial Data
SCL - Serial Clock
SQW/OUT - Square wave/Output Driver

DESCRIPTION

The DS1307 Serial Real Time Clock is a low power, full BCD clock/calendar plus 56 bytes of
nonvolatile SRAM. Address and data are transferred serially via a 2-wire bi-directional bus. The
clock/calendar provides seconds, minutes, hours, day, date, month, and year information. The end of the
month date is automatically adjusted for months with less than 31 days, including corrections for leap
year. The clock operates in either the 24-hour or 12-hour format with AM/PM indicator. The DS1307
has a built-in power sense circuit which detects power failures and automatically switches to the battery
supply.

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DS1307

OPERATION

The DS1307 operates as a slave device on the serial bus. Access is obtained b y implementing a START
condition and providing a device identification code followed b y a re gister address. Subsequent re gisters
can be accessed sequentially until a STOP condition is executed. When V

falls below 1.25 x V

CC

BAT

the

device terminates an access in progress and resets the device address counter. Inputs to the device will
not be recognized at this time to prevent erroneous data from being written to the device from an out of
tolerance system. When V
mode. Upon power up, the device switches from battery to V
recognizes inputs when V

falls below V

CC

is greater than 1.25 x V

CC

BAT

the device switches into a low current battery backup

when VCC is greater than V

CC

. The block diagram in Figure 1 shows the main

BAT

+0.2V and

BAT

elements of the Serial Real Time Clock.

DS1307 BLOCK DIAGRAM Figure 1

SIGNAL DESCRIPTIONS

VCC, GND - DC power is provided to the device on these pins. V
applied within normal limits, the device is fully accessible and data can be written and read. When a
3-volt battery is connected to the device and V

is below 1.25 x V

CC

However, the Timekeeping function continues unaffected by the lower input voltage. As V
V

the RAM and timekeeper are switched over to the external power supply (nominal 3.0V DC) at

BAT

V

.

BAT

- Battery input for any standard 3-volt lithium cell or other energy source. Batter y voltage must be

V

BAT

held between 2.0 and 3.5 volts for proper operation. The nominal write protect trip point voltage at which
access to the real time clock and user RAM is denied is set by the internal circuitry as 1.25 x V
nominal. A lithium battery with 48 mAhr or greater will back up the DS1307 for more than 10 years in
the absence of power at 25 degrees C.

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is the +5 volt input. When 5 volts is

CC

, reads and writes are inhibited.

BAT

falls below

CC

BAT

DS1307

SCL (Serial Clock Input) - SCL is used to synchronize data movement on the serial interface.

SDA (Serial Data Input/Output) - SDA is the input/output pin for the 2-wire serial interface. The SDA

pin is open drain which requires an external pullup resistor.
SQW/OUT (Square Wave/ Output Driver) - When enabled, the SQWE bit set to 1, the SQW/OUT pin

outputs one of four square wave frequencies (1 Hz, 4 kHz, 8 kHz, 32 kHz). The SQW/OUT pin is open
drain which requires an external pullup resistor. SQW/OUT will operate with either Vcc or Vbat applied.

X1, X2 - Connections for a standard 32.768 kHz quartz crystal. The internal oscillator circuitry is
designed for operation with a crystal having a specified load capacitance (CL) of 12.5 pF.

For more information on crystal selection and crystal layout considerations, please consult Application
Note 58, “Crystal Considerations with Dallas Real Time Clocks.” The DS1307 can also be driven by an
external 32.768 kHz oscillator. In this configuration, the X1 pin is connected to the external oscillator
signal and the X2 pin is floated.

Please review Application Note 95, “Interfacing the DS1307 with a 8051-Compatible Microcontroller”
for additional information.

RTC AND RAM ADDRESS MAP

The address map for the RTC and RAM registers of the DS1307 is shown in Figure 2. The real time
clock registers are located in address locations 00h to 07h. The RAM registers are located in address
locations 08h to 3Fh. During a multi-byte access, when the address pointer reaches 3 Fh, the end of RAM
space, it wraps around to location 00h, the beginning of the clock space.

DS1307 ADDRESS MAP Figure 2

00H

07H
08H

3FH

SECONDS

MINUTES

HOURS

DAY

DATE

MONTH

YEAR

CONTROL

RAM

56 x 8

CLOCK AND CALENDAR

The time and calendar information is obtained by reading the appropriate register bytes. The real time
clock registers are illustrated in Figure 3. The time and calendar 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. Bit 7 of Register 0 is the Clock Halt (CH) bit. When this bit is set to a 1, the
oscillator is disabled. When cleared to a 0, the oscillator is enabled.

Please note that the initial po w er on state of al l regi sters is no t def in ed . Th eref ore it i s i mportant to
enable the oscillator (CH bit=0) during initial configuration.

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DS1307

The DS1307 can be run in either 12-hour or 24-hour mode. Bit 6 of the hours register is defined as the
12- 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 second 10 hour bit (20­23 hours).

On a 2-wire START, the current time is transferred to a second set of registers. 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 of an update of the main registers during a read.

DS1307 TIMEKEEPER REGISTERS Figure 3

CONTROL REGISTER

The DS1307 Control Register is used to control the operation of the SQW/OUT pin.

BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0

OUT X X SQWE X X RS1 RS0

OUT (Output control): This bit controls the output level of the SQW/OUT pin when the square wave
output is disabled. If SQWE=0, the logic level on the SQW/OUT pin is 1 if OUT=1 and is 0 if OUT=0.

SQWE (Square Wave Enable): This bit, when set to a logic 1, will enable the oscillator output. The
frequency of the square wave output depends upon the value of the RS0 and RS1 bits.

RS (Rate Select): These bits control the frequency of the square wave output when the square wave
output has been enabled. Table 1 lists the square wave frequencies that can be selected with the RS bits.

SQUAREWAVE OUTPUT FREQUENCY Table 1

RS1 RS0 SQW OUTPUT

FREQUENCY

00 1 Hz
0 1 4.096 kHz
1 0 8.192 kHz
1 1 32.768 kHz

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