Microprocessor controlled capacitor discharge ignition system

In a capacitor discharge ignition system having an ignition system for an internal combustion engine which includes a permanent magnet group rotatable with the engine for generating pulses in a charge coil disposed on a leg portion of a ferromagnetic core and also having a primary winding and secondary winding of an ignition coil disposed on the same leg portion of said core and having a microprocessor disposed in close proximity with the ignition coil, the improvement comprising means for energizing the microprocessor by said pulses generated in the charge coil during each revolution of the engine shaft, means for amplifying and squaring the leading edge portions of said pulses and connecting the same to the input port of the microprocessor for determining the elapsed time occurring in the time interval between said leading edges, an output port of the microprocessor being connected to a gate electrode of a silicon controlled rectifier (SCR) for switching the SCR "on" in response to a predetermined spark advance programmed into the microprocessor and said elapsed time indicative of the rotational speed of the engine, and said program including a signal to turn "off" all input ports of the microprocessor for a time at least as long as the spark duration of the ignition system whereby the microprocessor is isolated from any interference caused by the ignition pulse being generated in the secondary winding of the ignition coil.