Author: wo xin ya time: 2019.04.03
CAN is the Controller local Area Network (Controller Area Network), it is by the development and production of automotive electronics products for German BOSCH company's development, and eventually become the international standard (ISO11519), is one of the most widely used field bus in the world,
CAN bus protocol has become the automobile computer control system and embedded industrial control bus LAN standards, and CAN as the underlying protocol designed for large trucks and heavy industry machinery vehicles J1939 protocol, in recent years, it has high reliability and good ability of error detection, computer control system is widely used in automobile and environment temperature, strong electromagnetic radiation and vibration of industrial environment,

One, two bus network
Closed-loop bus: follow the ISO11898 standard, Lmax=40 m, Hspeed=1 MBPS, bus requires a is at each end of the "120" resistance,
Open loop bus: follow ISO11519-2 standard, Lmax=1 km, Hspeed=125 KBPS, requirement each root bus there is a "2200" series of electric
Resistance,

Second, the difference signal
(stealth level) logic 1: CAN_High=CAN_Low=2.5, the VH - VL=0 v,
(dominant level) logic 0: CAN_High - CAN_Low=3.5-1.5=2 v,

Three, CAN deal a sequential
CAN protocol is a sequential=SS (synchronous) + PTS (transmission time) + PBS1 (phase buffer) + PBS2 (phase buffer)

Four, synchronously
Hard synchronization: bus time falling edge detection, falling edge translation to SS,
To resynchronize: phase advance (PBS1) or lag (PBS2) reduction, the purpose of synchronization are envoys points within the SS section contains up to jump down,
Change to resynchronize compensation Width SJW (reSynchronization Jump Width) value, the greater the permissible error increase, but the communication rate will decline,