DS1307

@@ -0,0 +1,52 @@+# DS1307++**Analog Devices** · I2C real-time clock · PDIP-8++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++- `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](https://cdn.sparkfun.com/datasheets/BreakoutBoards/DS1307.pdf) (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](docs/ds1307-datasheet.pdf)

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