10.2.1 Design Requirements

The High-Speed ISO 11898 Standard specifications are given for a maximum signaling rate of 1 Mbps with a bus length of 40 m and a maximum of 30 nodes. It also recommends a maximum unterminated stub length of 0.3 m. The cable is specified to be a shielded or unshielded twisted-pair with a 120-Ω characteristic impedance (ZO). The standard defines a single line of twisted-pair cable with the network topology as shown in Figure 29. It is terminated at both ends with 120-Ω resistors, which match the characteristic impedance of the line to prevent signal reflections. According to ISO 11898, placing RL on a node should be avoided because the bus lines lose termination if the node is disconnected from the bus.