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DS1307 Serial Real-Time Clock (RTC) Technical Summary
Overview
The DS1307 is a low-power, full Binary-Coded Decimal (BCD) clock/calendar with an integrated 56-byte nonvolatile SRAM. This component communicates via a 2-wire bidirectional I²C bus, making it an ideal solution for timekeeping applications requiring minimal power consumption and simple interfacing. The DS1307 provides accurate timekeeping with seconds, minutes, hours, day, date, month, and year information, including automatic leap-year compensation up to the year 2100.
Key Features
- Real-Time Clock (RTC): Counts seconds, minutes, hours, date of the month, month, day of the week, and year with leap-year compensation.
- 56-Byte Nonvolatile SRAM: General-purpose storage for system data.
- I²C Serial Interface: Supports standard (100kHz) and fast (400kHz) modes.
- Low Power Consumption: Operates on minimal current, making it suitable for battery-backed applications.
- Programmable Square-Wave Output: Configurable output signal at 1Hz, 4kHz, 8kHz, or 32kHz.
- Automatic Power-Fail Detection: Switches to backup supply when main power is lost.
- Wide Operating Voltage: Operates from 4.5V to 5.5V, with battery backup support down to 2.0V.
Applications
The DS1307 is widely used in applications requiring accurate timekeeping and data storage, including:
- Embedded systems and microcontrollers
- Data loggers and event recorders
- Point-of-sale (POS) terminals
- Medical devices
- Automotive systems
- Consumer electronics (e.g., digital cameras, smart appliances)
- Industrial automation and control systems
Electrical Characteristics
The following table summarizes the key electrical specifications of the DS1307:
Absolute Maximum Ratings
- Supply Voltage (VCC): -0.5V to +6.0V
- Storage Temperature: -65°C to +150°C
- Operating Temperature: -40°C to +85°C (industrial grade)
DC Electrical Characteristics
- Supply Current (Active Mode): 500µA (typical) at 5V
- Supply Current (Battery Backup Mode): 300nA (typical) at 3V
- I²C Bus Input Low Voltage (VIL): ≤ 0.3 × VCC
- I²C Bus Input High Voltage (VIH): ≥ 0.7 × VCC
AC Electrical Characteristics
- I²C Clock Frequency: 100kHz (standard mode), 400kHz (fast mode)
- Data Setup Time (tSU;DAT): 250ns (min)
- Data Hold Time (tHD;DAT): 0ns (min)
Functional Description
The DS1307 operates as a slave device on the I²C bus, responding to commands from a master controller. The timekeeping registers are updated automatically, and the device can operate in either 12-hour or 24-hour format. The 56-byte SRAM is accessible for general-purpose storage and retains data during power loss when connected to a backup battery.
Timekeeping Registers
The DS1307 includes the following timekeeping registers (all in BCD format):
- Seconds (00-59)
- Minutes (00-59)
- Hours (1-12 + AM/PM or 00-23)
- Day of Week (1-7)
- Date (1-31)
- Month (1-12)
- Year (00-99)
Control Register
The control register (address 0x07) configures the square-wave output (SQW/OUT pin) and enables/disables the oscillator. Key bits include:
- SQWE (Square-Wave Enable): Enables the square-wave output when set.
- RS1, RS0 (Rate Select): Sets the square-wave frequency (1Hz, 4kHz, 8kHz, or 32kHz).
Package Information
The DS1307 is available in an 8-pin PDIP or SOIC package. The pinout is as follows:
- Pin 1 (X1): 32.768kHz crystal connection
- Pin 2 (X2): 32.768kHz crystal connection
- Pin 3 (VBAT): +3V battery input for backup power
- Pin 4 (GND): Ground
- Pin 5 (SDA): I²C data line
- Pin 6 (SCL): I²C clock line
- Pin 7 (SQW/OUT): Square-wave output or open-drain output pin
- Pin 8 (VCC): +5V power supply
Mechanical Dimensions
- PDIP (8-pin): 9.81mm × 6.35mm body, 2.54mm pitch
- SOIC (8-pin): 5.00mm × 4.00mm body, 1.27mm pitch
Conclusion
The DS1307 is a versatile and reliable real-time clock solution for embedded systems, offering low power consumption, nonvolatile storage, and easy I²C interfacing. Its robust feature set and wide operating temperature range make it suitable for a broad range of applications requiring precise timekeeping and data retention.
