This invention relates generally to a timekeeping device operating from an internal oscillator circuit and more particularly to a timekeeping device having supplemental functions which can be accessed by an external unit for the performance of particular functions or the output of particular timing signals. The use of a microcomputer or microprocessor in systems having stored programs and data is rapidly expanding. Such systems make it possible to change specifications and requirements and to effect the processing of a plurality of different functions. If a timekeeping function is performed by the microcomputer itself, this apparatus is not so suitable for accomplishing multiple functions because while timekeeping, the microcomputer can perform no other operation. Therefore, it becomes necessary to resort to a timer system. In another operational system, accurate and periodic clock signals are imput in an interrupting mode so that the system is subjected to a timekeeping process during each interruption. However, according to this system the computer's central processing unit is continuously devoted to a duty cycle as a result of timekeeping processing. An interruption in the time measurements takes place during any real time processing so that the real time controlling operation becomes inaccurate. Another, and greater deficiency in present systems is that the microcomputer, because of its relatively high power consumption in operation, is likely to have its main switch turned on and off and to be rendered conductive and non-conductive while it is being transported. In the process, stored time information volatilizes and is lost. For this reason, an electronic timekeeping function desirably operates independently on a battery at reduced power and voltage so that it operates for extended periods of time even when a battery having a small capacity is used. In this way independent timekeeping accuracy is preserved.
What is needed is a timekeeping device for operation in cooperation with external units, such as a microcomputer or microprocessor, the timekeeping device maintaining its accuracy and providing a simple interface with the external unit.