This is known as the I.P.O. Principle.

I.P.O.

Status of switch is changed.
Changing switch status is sent to processor.
Processor looks at conditions which must be met.
If the processor deems the conditions for switch status change are met, a relay is signaled via a ground signal.
The relay is energized, the points are closed and the light bulb glows.

NOTE: The processor looked at other inputs before making the decision to activate the relay.

Fig 1: Identifying I.P.O. Principle

Courtesy of BMW OF NORTH AMERICA, INC.

Any device controlled by a processor requires input to the alert the operating program of a condition. The program processes the input information and logically activates an output of a component.

All BMW control systems are explained by the IPO principle. It is the key to understanding all BMW control system technologies.

Fig 2: I.P.O. Principle Display

Courtesy of BMW OF NORTH AMERICA, INC.