According to ISO 11898, in order to enhance the reliability of CAN-bus communication, the two endpoints of the CAN-bus network are usually added to the terminal matching resistance (120Ω).
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The size of the terminal matching resistance is determined by the characteristic impedance of the transmission cable. For example, if the characteristic impedance of the twisted pair is 120Ω, the two endpoints on the bus should also integrate the 120Ω terminal resistance.
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In the case of long-distance communication, the resistance of 120Ω may not be suitable, and it needs to be adjusted at this time.
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Take the standard 1.5 square mm wire diameter shielded twisted pair wire as an example: 1KM~2KM terminal resistance value of 120Ω; 3km-160ω; 4km-220ω; 10KM - 390Ω.
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Using the CANscope eye map analysis, we can directly observe the non-standard communication level amplitude caused by wire impedance and interference problems, so as to find out the cause of bus error.