Ds1307

DS1307
64 x 8 Serial Real-Time Clock
www.maxim-ic.com

FEATURES
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PIN ASSIGNMENT

Real-time clock (RTC) 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, battery-backed, nonvolatile (NV)
RAM for data storage
Two-wire serial interface
Programmable squarewave outputsignal
Automatic power-fail detect and switch
circuitry
Consumes less than 500nA in battery backup
mode with oscillator running
Optional industrial temperature range:
-40°C to +85°C
Available in 8-pin DIP or SOIC
Underwriters Laboratory (UL) recognized

ORDERING INFORMATION
DS1307
DS1307Z
DS1307N
DS1307ZN

8-Pin DIP (300-mil)
8-Pin SOIC (150-mil)
8-Pin DIP (Industrial)
8-Pin SOIC(Industrial)

X1

l

8

VCC

X2
VBAT

2

7

SQW/OUT

3

6

SCL

GND

4

5

SDA

DS1307 8-Pin DIP (300-mil)
X1

l

8

VCC

X2
VBAT

2

7

SQW/OUT

3

6

SCL

GND

4

5

SDA

DS1307 8-Pin SOIC (150-mil)

PIN DESCRIPTION
VCC
X1, X2
VBAT
GND
SDA
SCL
SQW/OUT

- Primary Power Supply
- 32.768kHz Crystal Connection
- +3VBattery Input
- Ground
- Serial Data
- Serial Clock
- Square Wave/Output Driver

DESCRIPTION
The DS1307 Serial Real-Time Clock is a low-power, full binary-coded decimal (BCD) clock/calendar
plus 56 bytes of NV 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 ofthe 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 AM/PM indicator. The
DS1307 has a built-in power sense circuit that detects power failures and automatically switches to the
battery supply.

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DS1307

TYPICAL OPERATING CIRCUIT

OPERATIONThe DS1307 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 a register address. Subsequent registers
can be accessed sequentially until a STOP condition is executed. When VCC falls below 1.25 x VBAT the
device terminates an access in progress and resets the device address counter. Inputs tothe 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 VCC falls below VBAT the device switches into a low-current battery backup
mode. Upon power-up, the device switches from battery to VCC when VCC is greater than VBAT + 0.2V
and recognizes inputs when VCC is greater than 1.25 x VBAT. The block diagramin Figure 1 shows the
main elements of the serial RTC.

DS1307 BLOCK DIAGRAM Figure 1

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SIGNAL DESCRIPTIONS
VCC, GND – DC power is provided to the device on these pins. VCC is the +5V input. When 5V is
applied within normal limits, the device is fully accessible and data can be written and read. When a 3V
battery is connected to the device and VCC is below 1.25 xVBAT, reads and writes are inhibited. However,
the timekeeping function continues unaffected by the lower input voltage. As VCC falls below VBAT the
RAM and timekeeper are switched over to the external power supply (nominal 3.0V DC) at VBAT.
VBAT – Battery input for any standard 3V lithium cell or other energy source. Battery voltage must be
held between 2.0V and 3.5V for proper operation. Thenominal write protect trip point voltage at which
access to the RTC and user RAM is denied is set by the internal circuitry as 1.25 x VBAT nominal. A
lithium battery with 48mAhr or greater will back up the DS1307 for more than 10 years in the absence of
power at 25ºC. UL recognized to ensure against reverse charging current when used in conjunction with a
lithium battery.
See “Conditions of...