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Safety-critical electronic control units within automotive applications, such as four-wheel-drive, anti-lock braking systems, and airbag systems, are all characterized by sophisticated internal and external monitoring circuitry. This paper is focused on the specific needs of monitoring circuitry in electronic control units (ECU) for airbag systems. After a short introduction, the main electrical components of an airbag system and their interconnections are described. In the following sections, the monitoring of components external to the ECU is discussed, such as the monitoring of the battery supply voltage, the warning lamp, the selection inputs, the firing loops, and external crash sensors. For each case, requirements are stated and practical solutions for the realization of the monitoring functions are provided. Furthermore, the pros and cons of simple and sophisticated solutions are compared.

In comparison to a standard dual airbag system as of today, future restraint systems will introduce a variety of new and additional actuator devices which help to improve the overall restraint performance. Furthermore, sensors and sensor-subsystems will be added to improve and extend the range of crash detection and to enable an automatic adaptation of the restraint system to a given status of the vehicle, its occupants and the crash severity. The implementation and control of these new functions require an appropriate design of the overall restraint system electronics. Two approaches are described in greater detail: the modular design based on functional building blocks, and the implementation as a distributed system including communication links.