Quote:
Originally Posted by Tristan Lall
Regarding the CAN bus, to some extent, there's always an aspect of star topology on the bus—but traditionally the stub length is short, possibly on the order of a couple of millimetres (in the case of a direct connection to an integrated CAN transceiver). Barring any strange internal arrangement on these controllers, if you leave one pair unconnected, you should still be able to make the connection downstream to the remaining pair, but your stub length will increase.
Here are some general suggestions for optimizing stub length, given other parameters. |
I think of a star topology as the line length being short (or 0) relative to the stub length. Very different than what the CAN spec recommends. Without doing the math, I think you can get away with something approaching a star topology in FRC because the entire bus length is short. I have also run just one terminating resistor without issues. But if I were to start having problems, one of the steps would be to make the bus wiring completely to spec.
Here is what the
CIA-- the organization that maintains the CAN standard, not the American government entity with the same name has to say.
Quote:
Network topology
This clause is most interesting for system designers.
Electrical signals on the bus are reflected at the ends of the electrical line unless measures against that have been taken. For the node to read the bus level correctly it is important that signal reflections are avoided. This is done by terminating the bus line with a termination resistor at both ends of the bus and by avoiding unnecessarily long stubs lines of the bus. The highest possible product of transmission rate and bus length line is achieved by keeping as close as possible to a single line structure and by terminating both ends of the line. Specific recommendations for this can be found in the according standards (i.e. ISO 11898-2 and -3).
...
|