What is CAN bus?

Controller Area Network (CAN) is a serial communication protocol that lets microcontrollers and devices talk to each other without a central host computer. Developed by Bosch in the 1980s, it is now the standard in automotive and heavy vehicle electronics. 
 Why buses use it 
 In a MAN Lion's City , dozens of ECUs (Electronic Control Units) share data in real time: the engine tells the instrument cluster the RPM, the EBS reports brake air pressure, the tachograph transmits vehicle speed — all over two wires (CAN_H and CAN_L). 
 The J1939 standard 
 Heavy vehicles (buses, trucks) use SAE J1939 , an application layer built on top of CAN. It defines: 
 
 
 
 
 Element 
 Description 
 
 
 
 
 29-bit ID 
 Extended identifier (vs 11-bit basic CAN) 
 
 
 PGN 
 Parameter Group Number — identifies the data type 
 
 
 SA 
 Source Address — address of the sending ECU (0x00–0xFE) 
 
 
 SPN 
 Suspect Parameter Number — each signal within a PGN 
 
 
 
 
 Implementation parameters 
 
 
 
 
 Parameter 
 Value 
 
 
 
 
 Bus speed 
 250 kbps 
 
 
 ID type 
 Extended (29-bit) 
 
 
 Send cycle 
 20 ms (50 Hz) 
 
 
 Transceiver 
 MCP2515 + TJA1050 
 
 
 MCP2515 oscillator 
 8 MHz 
 
 
 
 
 Note 
 0xFF bytes in unused positions are the J1939 default for "parameter not available" (SNA — Specific Not Available).