Understanding Smart Sensors - Nomads.usp

The Implications of Smart Sensor Standards 307standards, such as CAN, or pending standards, such as the drive-by-wire busTTP/C, were considered too expensive for the airbag application.The DSI is not designed to be fault tolerant, but it has a high immunityto EMI. The signal protocol uses voltage mode signaling in one direction (fromthe master) and current mode signaling in the other direction (from the slave).However, the DSI does not fail without warning. During powerup, each nodeis analyzed, and the airbag can be added or removed, depending on the presenceand the size of passenger, without completely reconfiguring the network.Configuration during powerup allows components from several differentsuppliers to be combined for the first time at vehicle assembly or to be replacedin service if they are found to be defective without special programmingequipment [17].Figure 13.8 is an example of the two-wire DSI network. The master nodepolls each sensor for information, calculates whether an airbag needs to bedeployed, and then issues a command to the appropriate actuator (squib). Thenetwork that connects to other networks in the vehicle is called the niche areanetwork (NAN).Figure 13.9 shows a DSI network with the various components of an airbagsystem [17]. Although the network is a NAN, 23 components are identifiedin the figure. The ability of automakers to add safety components, such asside-impact airbags, kneebags, tubular restraints, pretensioners, and occupantsensors without redesigning the entire system provides flexibility and saves timeand resources.Slave Slave Slave SlaveProgrammableaddressProgrammableaddressProgrammableaddressProgrammableaddressSlaveProgrammableaddressSlaveProgrammableaddressABPreprogrammedaddressSlavePreprogrammedaddressSlavePreprogrammedaddressSlaveSlaveProgrammableaddressMasterFigure 13.8 Example of a DSI. (After: [17].)