DS1307

DS1307 is a low-power I2C real-time clock/calendar IC. It keeps track of seconds, minutes, hours, day, date, month, and year, and provides 56 bytes of RAM plus a programmable 1 Hz–32 kHz square-wave output. It runs from 4.5–5.5 V and includes a VBAT backup input with a trickle-charge circuit, so timekeeping continues when power is off. A 32.768 kHz crystal (X1/X2) drives the clock, while the two-wire I2C interface (SCL, SDA) communicates with a 7-bit address of 0x68. Time/date data are read/written over I2C; the VBAT domain preserves time during battery operation. Applications include clocks, data logging, and timestamping. Pros: cheap, low power, simple. Cons: less accurate than newer RTCs (e.g., DS3231) and requires an external crystal plus a backup battery.

Equivalent RTCs to DS1307 (common substitutes):
- DS3231 (Maxim) — I2C, high accuracy (TCXO/temperature compensated).
- MCP7940N / MCP79410 / MCP79412 (Microchip) — I2C, battery-backed RAM.
- PCF8563 (NXP) — I2C RTC.
- ISL1208 / ISL1209 (Renesas/Intersil) — I2C RTC with SRAM.
- RV-3029-C2 (Epson) — I2C, alarms, VBAT.
- DS1302 (Dallas/Maxim) — 3‑wire interface (alternative family).

Key features of the DS1307:
- I2C real-time clock with 7-bit address 0x68 (standard-mode up to 100 kHz).
- Timekeeping with seconds, minutes, hours (BCD, 12/24-hour mode), day, date, month, year; uses a 32.768 kHz crystal.
- 56 bytes of battery-backed NV RAM (addresses 0x08–0x3F) accessible via I2C.
- Automatic power-fail detect and VBAT switchover; keeps time when main power is lost.
- Programmable square-wave output (SQW/OUT) with selectable frequencies: 1 Hz, 4.096 kHz, 8.192 kHz, 32.768 kHz (or disabled).
- Trickle-charge circuit for VBAT with external resistor/diode support.
- Operating supply: 4.5–5.5 V; low-power operation, suitable for battery-backup use.
- External crystal required for timekeeping (32.768 kHz).

Pin count: 8 pins (DIP-8/SO-8).
Pin functions (typical 8-pin layout): VCC, GND, SDA (I2C data), SCL (I2C clock), X1 and X2 (32.768 kHz crystal), VBAT (backup supply with optional trickle-charge), SQW/OUT (programmable square-wave output).
Function: DS1307 is an I2C real-time clock/calendar with 32 kHz crystal input, banked RAM (battery-backed, ~56 bytes), and a programmable square-wave output. It can keep time on VBAT when main power is lost and provides time/date registers via I2C.

Manufacturer: Dallas Semiconductor (original). Dallas Semiconductor was a US-based semiconductor company that designed and manufactured integrated circuits (ICs) for electronics. It was acquired by Maxim Integrated in 2001, and Maxim is now part of Analog Devices.

DS1307 is a battery-backed I2C real-time clock. Key application areas:
- Timekeeping and calendar in microcontrollers and embedded systems
- Data loggers and sensor networks requiring time-stamped measurements
- Alarms and timed control via the on-chip alarm or 1 Hz square-wave
- Time-stamping in instrumentation, test benches, and data-recording devices
- Battery-backed clocks in consumer electronics, appliances, medical devices, and automotive dashboards during power loss
- Simple clock/calendar modules for digital displays and automation controllers

DS1307 is an 8-pin device. Typical packages: DIP-8 (PDIP) and SOIC-8; some suppliers also offer MSOP-8 or TSSOP-8 variants. Check the exact package in the datasheet.