A novel scan generator for a scanning tunneling microscope (STM) has been developed. The instrument compares tunneling current with three thresholds values, to generate anx‐scanner signal with a dynamically changeable step size for adaptation to sharp topographical changes. It has two advantages compared to conventional STM scan generators (i) a better protection from a tip crash and (ii) minimization of the image acquisition time. The implementation is made with a digital signal processor (DSP) DSP32C from AT&T, mounted on a commercially available PC AT‐compatible plug‐in card. Test images of extremely rough surfaces confirm the usefulness of our novel scan generator. The concept could also be used for different scanning probe microscopes.