Quote:
Originally Posted by GeeTwo
The #2 problem is signal reflection from the "open" end. With short runs, the reflected signal level is probably well below the actual signal, and you'll do OK. As the bus gets longer, the difference between the reflected and direct level (that is, the signal to noise ratio) degrades.
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The relevant measure here isn't amplitude, it's time. A sufficiently short bus will have the reflection swallowed up by the terminated end quickly enough that the signal will not suffer. But if it's just a bit too long, the devices at the opposite end of the bus from the unterminated end can encounter enough interference to lose their ability to communicate.
That goes along with a good heuristic when trying to debug a high-speed bus like CAN: wiring problems near one end of the bus often produce symptoms at the other end.