Terminal resistance is an important configuration of CAN bus communication, and it is an important component affecting Module CAN-BUS communication. The CAN bus terminal resistance is generally 120Ω. In fact, during design, two 60Ω resistors are connected in series, and there are generally two 120Ω nodes on the bus. Why does the CAN bus need to add a terminal resistor?The role of terminal resistance:(1) Improve anti-interference ability and quickly pass high-frequency and low-energy signals.(2) Ensure that the bus enters the recessive state quickly and quickly passes through the energy of the parasitic capacitance.(3) Improve the signal quality and place it at both ends of the bus to reduce the reflected energy.The CAN bus has two states of "dominant" and "recessive", "dominant" represents "0", "recessive" represents "1", which is determined by the CAN transceiver.When the bus is "dominant", Q1 and Q2 inside the transceiver are turned on, and a voltage difference is generated between CANH and CANL; when it is "recessive", Q1 and Q2 are cut off, CANH and CANL are in a passive state, and the voltage difference isWhen the bus is loaded, the resistance of the differential resistor is very large when it is "recessive". External interference only requires a very small amount of energy to make the bus enter "dominant" (the minimum voltage of the dominant threshold of a general transceiver is only 500mV, and the voltage difference is 500mV, the bus is judged as "dominant"). When there is differential mode interference on the bus, there will be obvious fluctuations on the bus, and these fluctuations have no place to absorb them, and a dominant bit will be created on the bus.Therefore, in order to improve the anti-interference ability of the bus when it is recessive, a differential load resistor can be added, and the resistance value should be as small as possible to eliminate the influence of most noise energy. However, in order to avoid requiring too much current bus to enter "dominant", the resistance value should not be too small.
