Can bus resistor

The resistor for can bus is it usually put across the terminals on the 15 pin connector? I have two controllers do I need a resistor on both of them or do you just need one resistor for the whole system buss?

The more I read about CAN the more confusing it gets. For example in our case we usually have 2 to 4 controllers right next to each other, so the longest cable run will be about 40 cm. I've seen a lot of pages on a web claiming that with slow to average speed and short bus one 60 Ohm resistor works just as fine.

So, is it official recommendation to always use standard termination, even in cases like ours?

Standard CAN calls for 120 Ohm resistors at the ends of a string, but there are lots of systems about with short cables and/or slow speeds that get away without doing that. The Dynamic Controls DX wheelchair controller, for example, runs at ca. 100 kbp, has short runs often wired in a star configuration, and has no (external) terminating resistors (or distributed termination in all nodes - I've not tried to crack the internal circuitry). I have a 5 node CANbus system - 4 Arduino Nanos + a Roboteq - running at 500 kbp in a chain configuration with standard 2 X 120 Ohm at the ends, but the cable length is short (about 1 m end-to-end) and it actually runs reliably with only one 120 Ohm resistor, and with only some dropouts with no resistors at all. It will also run at 1M bps, but the scope shows a lot of noise so I dropped the speed down some. So the answer is: it depends. Wire it up as you wish, but then test with longer cables and higher speeds to make sure it still works reliably when pushed beyond where you intend to use it.

Reading the Dynamic DX systems manual this morning, I realized that what I said above was misleading. The Dynamic wheelchair controller system has two modules that have internal termination resistors and that are used in every installation, the other modules do not. The only deviation from standard CAN setup is that they recommend a star rather than chain configuration so that the terminators are not at the ends of a chain.