Can Bus Clause Samples

Can Bus. ‌ The complexity of the electrical architecture has started to increase in the begin- ning of ‘90s and many proprietary solution began to pop up. It became clear rather fast, that there is a need of a unified solution. Talking about complexity, in a E&E architecture 25-30 years ago the presence of a handful of ECUs was considering as complex. Nowadays, more than 80 ECUs are part of the electrical architec- ture. CAN protocol is considered simple and became standard and mandatory in automotive industry since 2008 [28]. On the physical layer, it runs on copper wires (twisted pair or wires) and uses the “differential signalling” method by having a CAN High (▇▇▇▇) and CAN Low (CANL) line (2 wires). In simple words as you can see in 2.4, when data are about to be transmitted, the CANL line drops the voltage of the signal and the CAN High line increase the voltage [28] [16] [32]. This approach has been adapted by CAN, due to the Electromagnetic Com- patibility (EMC) protection of the channel. Fault tolerant systems, usually follow this approach. As it is obvious in Figure 2.4, the initial voltage (“resting”) of the channel is 2,5 volts. When data are about to be transmitted the voltage levels fluctuate 1V (+1V in ▇▇▇▇ and –1V in CANL). The physical layer requires to be terminated in both ends by using a 120ohm resistor [28] [16] [32]. Figure 2.4: CAN High and CAN Low The CAN has different baud rates, which are configured by both receiver and transmitter. Some typical baud rates are 125kbps, 250Kbps, 500Kbps and 1Mbps. The transmission is serial (serial bit stream) and the duration of one bit depends on the baud rate. In order to deduct the duration of a bit, it is needed to calculate the bit time duration = 1Bit Rate, which for 125kbps equals to 8 µs [28] [16]. [32] Another interesting fact, about the addressing of CAN bus it is the addressing schema, which is broadcast. All nodes of a CAN bus network are listening in all the frames which are transmitted on the bus. Every CAN node “has acceptance filters” where they filter the messages, which are supposed to be processed by the application in each ECU. Below there will be a further elaboration on how the packets are crafted. It also needs to be considered the fact that, the complete set of the messages/packets are received by all CAN controllers even the ones which, eventually will not ”pass” the filter [28] [16] [32]. The CAN bus protocol, has 2 different representations when trasmits informa- tion into packets...