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DS1307 IC Pin diagram and description

PINs of DS1307







VCC - Primary Power Supply

X1, X2 - 32.768kHz Crystal Connection

VBAT - +3V Battery Input                                             

GND - Ground

SDA - Serial Data

SCL - Serial Clock

SQW/OUT - Square Wave/Output Driver



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 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 AM/PM indicator. The DS1307 has a built-in power sense circuit that detects power failures and automatically switches to the battery supply.


·       Real-time clock (RTC) counts seconds, minutes, hours, date of the month, month, day of the week, and with leap-year compensation valid up to 2100.

·       56-byte, battery-backed, nonvolatile (NV) RAM for data storage.

·       Two-wire serial interface.

·       Programmable square wave output signal.

·       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.


The 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 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 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.




VCC, GND – DC power is provided to the device on these pins. VCC is the +5V input.

VBAT – Battery voltage must be held between 2.0V and 3.5V for proper operation.

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.

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 (1Hz, 4kHz, 8kHz, 32kHz).

X1, X2 – Connections for a standard 32.768 kHz quartz crystal.


The accuracy of the clock is dependent upon the accuracy of the crystal and the accuracy of the match between the capacitive load of the oscillator circuit and the capacitive load for which the crystal was trimmed.


The address map for the RTC and RAM registers of the DS1307 is shown in Figure-1.                                                Figure-1


The time and calendar information is obtained by reading the appropriate register bytes. 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 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. The DS1307 can be run in either 12-hour or 24-hour mode.