The edge detection circuit is comprised of two crude differentiating amplifiers, one repsonding to the positive edges and one to the neagtive edges. Their outputs are joined in an OR configuration such that every edge generates a pulse.

The direction signal is derived by first taking the sign of the waveform, and then applying a small delay such that the output lags a small amount in time. Thus when the step pulse arrives, the direction signal reflects the sign of the waveform immediately prior to the edge.

The enable circuit is comprised of a window comparator which deteects activity at the input. When the comparator is low, it discharges a capacitor through a diode. When the comparator is high, the capacitor charges though a pullup resitor until the output comparator is tripped. This holds the output low until the input has been inactive for a moment. The enable signal is active low.