The scan counter is driven by an internal oscillator whose frequency is determined by a capacitor connected between Oscillator input and Scan input. An external scan clock applied to Scan input can also drive the scan counter. Scan counter advances on negative edge of scan clock. The counter scans from MSD to LSD. When Scan Reset input is brought high the scan counter is forced to MSD state. Internal synchonization guarantees proper scanning no matter when Scan Reset is brought low relative to scan clock. Maximum scan frequency is 500kHz.