To accurately determine the dwell time as well as the ignition instant in a digitally controlled ignition system to provide essentially constant ignition energy to a spark plug, and permit ready adjustment and matching of a basic system to various types of internal combustion engines, a counter is controlled to count up at a rate depending on speed of the engine starting from a predetermined angular position of the crankshaft of the engine with respect to a piston, then count down at a second rate, which may be fixed; a fixed number is introduced into the counter which changes the count state during either the first or the second count cycle, or upon transition of counting from the first to the second count cycle, the determination of the number being readily changed by specific connection of output terminals from the counter to a decoding stage, thus avoiding the necessity of reconnecting the internal wiring of a group of gates to match the system to any given engine.