Abstract: An apparatus for automatically changing the operation of a dual-mode digitizer tablet system. The system comprises a cordless pen device generating an electromagnetic wave of a variable frequency and a cordless mouse device generating an electromagnetic wave of a different frequency. The cordless pen device operates in an absolute mode and the cordless mouse device operates in a relative movement mode. The apparatus comprises a detection loop sensing circuit for detecting electromagnetic waves and a signal processing circuit for extracting the signal of either the pen device or the mouse device. The extracted signal is rectified and digitized for determining the position of the cordless pointing device by a micro-controller. A frequency counter determines the frequency of the detected signal. By detecting and determining the frequency of the electromagnetic wave received in the tablet system, the operation mode is adjusted automatically.