Abstract: Apparatus for detecting the direction of rotation of a crankshaft of an internal combustion engine. The crankshaft drives wheels associated with sensors for developing two pulse trains as the crankshaft rotates. One pulse train is a square wave having consecutively occurring high and low periods of equal angular duration. The other pulse train is a square wave having a plurality of spaced window pulses of unequal angular duration. The relative high and low logic states of the pulse trains at certain window locations has one relationship for forward movement of the crankshaft and a different relationship for reverse movement of the crankshaft. These relationships are detected. At one of the window locations, the relative high and low logic states of the pulse trains is the same for either forward or reverse rotation. Engine reversal at this location is detected by detecting the occurrence of two consecutively occurring relative logic states that are the same.