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                11                    FUTURE AUTOMOTIVE ELECTRONIC SYSTEMS




                                      (T/R) unit. Whenever the CPU requires data from any sensor, it sends a coded
                                      message on the bus, which is connected to all T/R units. However, the message
                                      consists of a sequence of binary voltage pulses that are coded for the particular
                                      T/R unit. A T/R unit responds only to one particular sequence of pulses, which
                                      can be thought of as the address for that unit.
                Each sensor in a multi-   Whenever a T/R unit receives data corresponding to its address, it
                plexing system sends its   activates an analog-to-digital converter. The sensor’s analog output at this
                individual data over a   instant is converted to a digital binary number as already discussed. This
                common bus. The com-  number and the T/R unit’s address are included so that the CPU can identify
                puter identifies the sen-  the source of the data. Thus, the CPU interrogates a particular sensor and then
                sor by signaling each   receives the measurement data from the sensor on the data bus. The CPU then
                sensor with a unique   sends out the address of the next T/R unit whose sensor is to be sampled.
                address.
                                      Control Signal Multiplexing
                                          It also is possible to multiplex control signals to control switching of
                                      electrical power. Electrical power must be switched to lights, electric motors,
                                      solenoids, and other devices. The system for multiplexing electrical power
                                      control signals around the vehicle requires two buses—one carrying battery
                                      power and one carrying control signals. Figure 11.17 is a block diagram of such




                 Figure 11.17
                 Control Signal
                 Multiplexing Block
                 Diagram











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                390                   UNDERSTANDING AUTOMOTIVE ELECTRONICS
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