When the switch is open, the input voltage is determined by the lock-in resistor. In the vehicle-mounted ECU with severe electromagnetic interference and other harsh environments, it is necessary to set up a reasonable filter circuit to prevent electromagnetic interference. Second, by preinstalling software etc. in the microcontroller, it is also possible to prevent abnormal operation caused by electromagnetic interference.
In the vehicle environment, there are cases where different voltages (battery voltage, ECU internal power supply voltage) are mixed and input, and these power supply voltages need to be separated. The ECU also needs to control the input of many ON/OFF signals, and some will combine multiple input signals and input them to the microcontroller through serial port communication. Therefore, these control functions are integrated into an IC (integrated circuit), and the size of the ECU is reduced.