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I am working at a project which requires an application which has some devices connected through a bus (RS-485 || CAN), I haven't decided yet.The problem is that some of this devices are hot pluggable and I don't know which devices to have the termination resistor.The bus is formed by 2 or 3 devices and I could disconnet almost all of them(only the one end will remain), so I think what happens if I disconnect the device with the termination resistor, I know that a differential bus has two termination resistor, one in each end.Could you give me some ideas how I can fix this issue ?

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    \$\begingroup\$ Simply, you install the resitor at both ends of the bus. When you unplug the device, the bus cable remains where it was. \$\endgroup\$
    – Marko Buršič
    Commented Nov 24, 2015 at 10:57
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    \$\begingroup\$ Attention: CAN communication won't work if there's single device on bus. CAN requires at least 1 reciever to transmit the data (ACK bit the frame!) \$\endgroup\$
    – Swanand
    Commented Nov 24, 2015 at 11:13
  • \$\begingroup\$ I will try to make a RS-485 communication with 9-bit, and the last bit will decided if message is a control or data. \$\endgroup\$
    – Stefan Merfu
    Commented Nov 24, 2015 at 11:14
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    \$\begingroup\$ If there is an option to choose between CAN and RS-485, you should always go with CAN since it is so rugged - it is especially suitable for plug & play systems (if you have given it some thought on the system level). Only reason to choose some old RS-485 technique is either if you need very high speeds/lots of data (where you should probably consider something ethernet-ish instead) or if you need to interact directly with some PC with no adapter in between. \$\endgroup\$
    – Lundin
    Commented Nov 24, 2015 at 15:16
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    \$\begingroup\$ You not only can but should install it at the end of the bus. If the plug & play module can be put anywhere, then it doesn't make sense for it to have termination by default. So either put the resistors outside the modules, or design the modules in a clever way which allows you to enable/disable on-board termination (by setting a jumper, flipping a dip-switch, connecting a wire etc). \$\endgroup\$
    – Lundin
    Commented Nov 27, 2015 at 7:28

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Pluggable devices implies that there is some system level infrastructure to allow the the connections to occur. That may be some type of cable system, back plane or daughter board setup. The termination resistor setup in such system is best solved by including the resistors into the system level infrastructure instead of attempting to place it directly on the pluggable devices.

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