A simple, battery-backed real-time clock with an I2C interface, in DIP-8, the chip on the ubiquitous 'Tiny RTC' modules. It keeps seconds through years in BCD with automatic leap-year handling and a 12/24-hour mode, backed by 56 bytes of general-purpose non-volatile RAM. A coin cell on VBAT keeps time running when main power is off, drawing only a few hundred nanoamps. A 32.768 kHz crystal on X1/X2 sets the timebase, and a programmable square-wave output (1 Hz, 4/8/32 kHz) can clock other logic. Unlike the DS3231 it has no built-in temperature-compensated oscillator, so accuracy depends on the external crystal. Runs 4.5-5.5 V (main).

Pinout

Pin	Name	Type	Function
1	X1	input	Connection for a standard 32.768kHz quartz crystal (C_L = 12.5pF). X1 is the input to the internal oscillator and can optionally be connected to an external 32.768kHz oscillator (with X2 left floating).
2	X2	output	Connection for the second terminal of the 32.768kHz quartz crystal. X2 is the output of the internal oscillator; leave floating if an external oscillator drives X1.
3	VBAT	power_in	Backup supply input for a standard 3V lithium cell or other energy source (2.0V to 3.5V, typ 3V). Powers the RTC and SRAM when VCC is removed; must be grounded if a backup supply is not used. Nominal power-fail trip point is 1.25 x VBAT.
4	GND	power_in	Device ground reference. All voltages are referenced to this pin.
5	SDA	bidirectional	I2C serial data input/output. Open-drain output requiring an external pullup resistor; pullup voltage may be up to 5.5V regardless of VCC. Bus capacitance is limited to 400pF and pin capacitance is <=10pF.
6	SCL	input	I2C serial clock input (0 to 100kHz). Synchronizes data movement on the serial interface. Requires an external pullup resistor; pullup voltage may be up to 5.5V regardless of VCC.
7	SQW/OUT	output	Square-wave / output driver. When SQWE is set to 1, drives one of four square-wave frequencies (1Hz, 4kHz, 8kHz, 32kHz). Open-drain output requiring an external pullup (up to 5.5V); operates from either VCC or VBAT. May be left floating if unused.
8	VCC	power_in	Primary power supply (4.5V to 5.5V, typ 5.0V). Full read/write access to the device is enabled when VCC is within operating range; when VCC falls below 1.25 x VBAT the device switches to battery-backup mode and timekeeping continues from VBAT.

Key specifications

Parameter	Value
Type	I2C real-time clock (RTC)
Timekeeping	seconds to year, BCD, leap-year
NVRAM	56 bytes general-purpose
Backup	VBAT coin-cell (keeps running)
Interface	I2C
Timebase	external 32.768 kHz crystal
Output	programmable square wave (1 Hz-32 kHz)
Package	PDIP-8

Ordering variants

Same part, different packaging or reel option.

DS1307N+ (PDIP-8)
DS1307Z+ (SOIC-8)

CAD (KiCad official)

Symbol: Timer_RTC:DS1307+
Footprint: Package_DIP:DIP-8_W7.62mm
3D model: DIP-8 (KiCad packages3D)

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

Datasheet: Analog Devices datasheet (14 pp, sha256 4114781b89b9a71a, retrieved 2026-08-17, tier: manufacturer)
Extractor: ds2sf (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF