A scan controller provides a translation between a two terminal external interface and a four signal line internal scan interface to a digital core of the integrated circuit. The two terminal external interface has an input terminal and an input/output terminal. The input terminal receives a clock signal and the input/output terminal serially receives a scan enable signal and a scan in data bit. A state machine controls the scan controller. The scan in data bit, the scan enable signal, and a scan clock signal are supplied in parallel to the internal scan interface. The digital logic provides a scan out data bit and the scan controller supplies the scan out data bit over the input/output terminal in synchronism with the clock signal.