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Originally Posted by Alan Anderson
The terminator resistor value is not arbitrary. It's chosen to match the "characteristic impedance" of the CAN bus wiring. If the impedances do not match, some of the high-frequency signal will be reflected at the end of the bus. Reflected signals interfere with signals sent later. This Stack Exchange question has some good answers.
Of course, the CAN wiring used in an FRC robot isn't exactly standardized, so the value is more of a good idea than a perfect number. |
Alan, when I said "arbitrary" I was referring to this statement in the very link you posted:
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Why it's 120 is simply a function of the design limited by physical size. It isn't specifically important which value they picked within a broad range (for example, they could have gone with 300 Ohms). However, all devices in the network have to conform to the bus impedance, so once the CAN standard was published there can be no more debate.
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Apologies for the ambiguity.