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NOVEMBER 2021 AFTERMARKET 25 www.aftermarketonline.net A voltage is measured at the output point when any one or both transistors are switched on. Please note the output is connected upstream of the resistor. Next, refer to Fig.7, which shows a NOT gate. This differs from both the AND/OR gates because there is only one input, as with other versions there is only one output. The NOT gate is also referred to as an inverter. This is because the output is the inverse of the input. When a logic 0 is applied to the base of the transistor, the output is logic 1. So, when the transistor is switched off, a voltage is available at the output point. The reason this device works is because the resistor is connected between the 5-volt supply and the collector of the transistor. Note, there will be no volt drop across the resistor if current is not flowing within the collector/emitter circuit. When the transistor is switched off there is no path to ground for the current to flow. A simplified practical example of a AND, OR and NOT Gate is displayed in Fig.8, Fig.9 and Fig.10. Meanwhile, Fig.11 shows an example of a Controller Area Network (CAN) Bus waveform. CAN bus uses a different method to assign a numerical value to the bus voltages. A dominant bit, of zero is set, when the CAN High voltage is 3.5 volts and the CAN Low voltage is 1.5 volts. The recessive state, given a value of 1 is when the voltage on both CAN High and CAN Low is 2.5 volts. The binary system is still fundamental to the operation of the system. Lastly, Fig.12 is an example of a Local Interconnect Network (LIN) Bus waveform. LIN Bus has an idle voltage of approximately battery voltage. During communication the module pulls the Bus voltage towards ground potential, this is a dominant (1) bit. To ensure correct message timing the master LIN node synchronises the other modules on the network with a 10- bit Synchronisation field. LIN Bus status vs voltage levels: Dominant State – Level 0 – Bus Low (Low Voltage). Recessive State – Level 1 – Bus High (High Voltage). Fig.8 Fig.9 Fig.10 Fig.11 Fig.12 Fig.7 Control modules operate on the principle of Boolean logic, i.e. the Binary System ”