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Real-Time Clock

For the 89S8252 Flash Micro Board

Real-Time Clock
This article was an entry to the Flash Competition of Elektor Electronics, and describes how a real-time clock (RTC) can be implemented in software, without using any dedicated RTC peripheral ICs. Since we also have to take account of drift, summertime and wintertime, an automatic synchronisation has been included with the DCF time signal transmitted from Frankfurt, Germany (range 1,000 miles).All of the operations of this ‘circuit’ happen at the interrupt level. In this way it can be added easily to a larger application where it provides the correct time without disturbing the main program. Since a DCF receiver is used to obtain the time, there is no need for any buttons to set the time when the microprocessor system is started. An application has been included as an example. Every second it:–updates the LCD display with the correct time,–transmits the time through the serial port. To polish this project off, a Windows program was written (in Visual Basic), which displays this time on the PC screen and sets the PC clock.
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