Data processing unit having multiple-purpose port used as a resonator connection port in first mode and as a data i/o port in second mode

摘要

For allowing a port to serve as not only one of the system clock input port but also a data input/output port, there is disclosed a data processing unit comprising a system clock supplying circuit operative in an internal oscillation mode or a transmission mode depending upon a mode selecting signal, a shifting circuit operative to provide an electrical path between two ports and the system clock supplying circuit in the internal oscillation mode but to provide another electrical path between one of the two ports and a data input/output line in the transmission mode, so that one of the ports serves between the clock input port and the data input/output port depending upon the mode selecting signal.