When a blade is in position in the air gap, the Hall generator and the IC are shielded from the magnetic field. The signal voltage is not switched and transistor T.0. is off. The base of transistor T.1. is positive, and a small current flow through the base / emitter, allows a heavier current to flow, through the collector / emitter.
This heavier current then flows through the base/emitter of T.2. and T.2. is switched 'ON'. Current can now flow through the ignition coil primary winding and through the collector/emitter of T.2. to ground. This completes the primary circuit and establishes the magnetic field in the ignition coil.
With distributor rotation, the blade exits from the air gap and a window enters.
The magnetic field at the Hall assembly now permeates the Hall generator ant it's integrated circuit and the signal voltage turns on the base / emitter of T.0.
The circuit, now established through the collector / emitter of T.0., diverts current away from the base circuit of T.1. and T.1. switches off. Since T.2. cannot function without the action of T.1., T.2. also switches off. This breaks the primary circuit, generating a self-induced voltage in the primary winding, a mutually induced voltage in the secondary winding, and creating a spark at the spark plug.
Maximum primary current flow and dwell angle are controlled by the ignition module. With continuous rotation, the primary circuit is established and interrupted as each blade enters and leaves, providing a spark for each cylinder in turn.
Ignition advance according to engine speed and load is provided by a centrifugal and vacuum advance mechanisms.
Engines with engine managment systems don’t use centrigual and vacumm advance mechanisms. Precise control of ignition advance according to engine load and engine speed is provided by the engine management electronic control unit or ECU.