Method of controlling a microprocessor to monitor input signals at irregular mutually intersecting intervals

Control of a microcomputer performing a wide variety of functions in a motor vehicle in which the sequences of input and output signals intersect in time, instead of being performed by an elaborate input/output unit, is performed in the microcomputer itself with the help of a timing signal generator operating at a sub-multiple of the microcomputer clock frequency and producing a sequence of timing signals, each of which serve as an interrupt signal to the microprocessor of the microcomputer to initiate an interrupt program for scanning inputs and preparing outputs. After this short interrupt program, the main program is resumed. In the interrupt program each of a number of registers, respectively serving separate inputs or outputs, are decremented or incremented, having been set at particular values at the beginning of each interrupt program. Some registers are set at two different values in alternation in succeeding interrupt intervals. Engine speed determination is produced by counting the number of interrupt signals during the passage of a prolonged signal representing a certain angle of shaft rotation. The frequency of timing signals is varied in steps in accordance with engine speed.