Why it is necessary to put two 120 ohm termination resistors at each end of CAN transmission line respectively? Does it make an equivalent resistance of 60 ohm? (parallel resistors). Is it OK to put only a single resistor at any end or in middle of this transmission line?

CAN Transmission Line with two termination resistor at both ends

  • \$\begingroup\$ @MichelKeijzers : I would like to know if putting two 120 Ohm resistors in parallel; let it be on both ends of line; does make effective impedance of 60 Ohms? \$\endgroup\$
    – Akky
    Oct 25 '18 at 11:17
  • \$\begingroup\$ I don't know all details, but the main reason is to stop unwanted signals echoing back through the line, that is why there should be a resistor at both ends. The duplication link show why it should be 120 ohm. \$\endgroup\$ Oct 25 '18 at 11:26
  • \$\begingroup\$ It is not OK to put only single resistor at one end or in middle. It must be connected at both ends to avoid standing waves. \$\endgroup\$
    – Swanand
    Oct 25 '18 at 12:20
  • \$\begingroup\$ en.wikipedia.org/wiki/… \$\endgroup\$ Oct 25 '18 at 14:00

If you want to avoid data reflections from either end of the cable you'll need to terminate those open ends in the characteristic impedance of the cable. As far as reflections are concerned the two impedances are not in parallel. At DC they are but at data transmission edge speeds they are not.


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