Abstract: A real-time application (RTA) is an application program that functions within a time frame also called real-time computing (RTC). A real-time clock/calendar is an essential part of many computer data acquisition and control systems. The things that need to be done in specific time with accuracy can be controlled by a embedded system. Such system provides accuracy in microsecond or Pico second. Such system uses high speed microcontroller (On chip CPU, RAM, ROM, oscillator, Timers etc.). This paper presents designing of automatic controlling circuit for PC based data acquisition for extended-Compound Astronomical Low-cost Low-frequency Instrument for Spectroscopy and Transportable Observatory (e-CALLISTO) to operate in specific time period. Microcontroller P89v51RD2 is interfaced using I2C Protocol with Dallas real-time clock/calendar (RTC) DS1307. The interfacing circuit diagram, PCB layout, flow-chart, C program, and use of it for controlling the PC to acquire the e-CALLISTO data are described. The main advantages of a real-time clock are that it keeps track of true time independent of software execution speeds, save electricity and requirement of memory storage.

Keywords: Embedded system, Microcontroller, RTC, I2C protocol, Data acquisition system, Computer, CALLISTO.