# A Digitalization Algorithm Based on the Voltage Waveform of the Multifunction Vehicle Bus
## 2 The MVB Voltage Waveform Digitalization Algorithm  
### The MVB Bus and Its Data Characteristics  
The MVB bus is a vehicle-level bus of the TCN, and the equipment mounted on the bus includes a traction system, an air conditioning system, a door system, etc. Therefore, the MVB bus is responsible for information transmission and communication between important devices in a car. The MVB bus is equipped with redundant lines, which are divided into supervisory lines and trust lines, both of which transmit the same information at the same time for the receiver to verify the reliability of communication data. The MVB bus has a transmission rate of 1.5 Mbit/s and transmits content using Manchester encoding.  
The MVB bus topology is shown in Figure 1. The media of the MVB network are mainly selected according to the communication transmission distance, including ESD (<20 m), EMD (<200 m) and OGF (<2000 m). This research chose an MVB based on EMD media. Since the EMD is the mainstream transmission medium, it is the most representative.  
Based on the EMD, voltage signals are used to transmit information between MVB devices, and link-layer data are used for internal analysis and processing of devices. Data at the data-link layer exist in binary form, while voltage signals at the physical layer transmit information by Manchester encoding. In addition, there are non-data symbols in the transmission process as delimiter bits. Figure 2 shows the encoding format of data and non-data symbols. One of the characteristics of Manchester coding is that there is a transition edge in the middle of the bit cell, which expresses the meaning of the data and is also a clock synchronization signal. With the help of this clock synchronization feature, each data bit can be located in the decoding process, avoiding error accumulation.  
The MVB network polls MVB devices to access different kinds of information. The polling master is the MVB master device and the information sent out is called the master frame, while the polled device is called the slave device and the information sent out is called the slave frame. MVB frame formats are shown in Figure 3.  
Figure 1: Topology of MVB.  
Figure 3: MVB frame formats: (**a**) format of master frame; (**b**) format of slave frame.  
Figure 2: The encoding format of data and non-data symbols: (**a**) non-data symbol encoding; (**b**) “0” and “1” data encoding.  
In addition, physical-layer waveform data have waveform features; IEC61375-3-1 [4] defines MVB physical-layer voltage waveforms in terms of a variety of features, and a software algorithm is used to extract the following features:  
* Steady-state amplitude: The steady-state amplitude of the MVB physical-layer waveform shall be at least \(\pm\)1.5 V when connected to the heavy test circuit and at most \(\pm\)5.5 V when connected to the light test circuit;
* Overshoot: The overshoot of the waveform, defined as the ratio of the difference between the maximum value of the waveform and the steady-state amplitude to the steady-state amplitude, shall not exceed 10%;
* Positive and negative steady-state amplitude difference: Defined as the difference between the positive steady-state amplitude and the negative steady-state amplitude in two consecutive pulses, it shall not exceed 0.1 V;
* Slew rate: The slew rate of the waveform, defined as the rate of change of the waveform within 100 ns of the zero crossing, shall be more than 15 mV/ns;
* Edge distortion: The edge distortion, defined as the time difference between the idealized and the actual zero crossing, shall not exceed 2% of one bit time.
* A diagram of waveform features is shown in Figure 4.