Application of serial clock DS1305 in field self-contained equipment

Many field observation instruments operate for extended periods in remote environments, requiring self-contained power solutions. While some devices can harness renewable energy like solar or wind, many rely on internal batteries. This makes efficient power management a critical design challenge.

This article explores the use of the Dallas DS1305 serial real-time clock (RTC) in self-powered field instruments. The DS1305 is ideal for applications where low power consumption and precise timing are essential. By integrating this chip, devices can minimize energy use by waking up only when necessary, significantly extending battery life.

In projects such as the National Marine 863 Program 818, we applied the DS1305 to manage power in marine monitoring equipment. These systems must collect data at specific times, then return to a low-power state. The DS1305 enables precise scheduling, ensuring that the main system only powers up when required. This approach reduces overall energy usage and allows the device to function for months or even years on limited battery capacity.

1. Basic Working Principle of the DS1305 Real-Time Clock

1.1 Main Functions of the DS1305 Serial RTC

The DS1305 offers several key features:

• Calendar and clock with year, month, day, hour, minute, second, and week up to 2100;
• 96 bytes of non-volatile RAM for user data storage;
• Two programmable alarm outputs;
• Dual power supply (main and backup);
• Operates on 2.5V to 5.5V;
• Wide operating temperature range (-40°C to +85°C).

1.2 Pin Configuration and Functionality

The DS1305 has 20 pins, including power inputs, crystal connections, interrupt outputs, and SPI/3-wire interface lines. Key pins include VCC1 and VCC2 for power, X1/X2 for the 32.768kHz crystal, and CS/SCLK/SDI/SDO for communication. It also includes a power-fail output (PF) and two interrupt pins (INT0 and INT1).

1.3 Internal Structure

The internal architecture of the DS1305 includes power control, a crystal oscillator, an SPI interface, memory registers, and a calendar/clock block. This design ensures accurate timekeeping while maintaining minimal power consumption.

1.4 Register Map and Memory Allocation

The DS1305 uses a 128-byte memory map, with 64 bytes dedicated to the calendar clock and 32 bytes for user RAM. The remaining space is reserved for control and status registers.

1.5 Register Definitions and Functions

Key registers include the Control Register (for enabling the oscillator and setting interrupts), the Status Register (to monitor alarm conditions), and the Trickle Charge Register (for managing battery charging). These allow flexible configuration and precise control over the device's operation.

1.6 Interface Modes

The DS1305 supports both SPI and 3-wire modes. In SPI mode, data is transferred using SCLK, SDI, and SDO. In 3-wire mode, the same lines are used for both input and output. Multi-byte transfers are supported, making it easy to read or write multiple registers at once.

2. Interface with AT89C2051

Connecting the DS1305 to the AT89C2051 microcontroller is straightforward. The SPI interface allows for simple integration, enabling the microcontroller to read time data and trigger alarms based on programmed intervals.

3. Application in Marine Environmental Monitoring

Marine monitoring systems often require long-term operation with limited power. Using the DS1305, we designed a power management unit that wakes up the system at scheduled times, collects data, and then returns to sleep. This method significantly reduces power consumption, allowing the device to operate for extended periods on a single battery charge.

By leveraging the DS1305’s low-power design and programmable alarms, our solution proved effective in the National Marine 863 Program 818. The system successfully monitored suspended sediment concentration in the ocean, demonstrating the viability of this approach for other field-based applications.