SLLS983J June 2009 – September 2019 ISO1050
The ISO11898 standard specifies the interconnect to be a single twisted pair cable (shielded or unshielded) with 120-Ω characteristic impedance (ZO). Resistors equal to the characteristic impedance of the line should be used to terminate both ends of the cable to prevent signal reflections. Unterminated drop-lines (stubs) connecting nodes to the bus should be kept as short as possible to minimize signal reflections. The termination may be in a node, but if nodes may be removed from the bus, the termination must be carefully placed so that it is not removed from the bus.
Termination may be a single 120-Ω resistor at the end of the bus, either on the cable or in a terminating node. If filtering and stabilization of the common mode voltage of the bus is desired, then split termination may be used. (See Figure 29). Split termination improves the electromagnetic emissions behavior of the network by eliminating fluctuations in the bus common-mode voltages at the start and end of message transmissions.