Kontron PCI-COM-8ULP, Руководство пользователя

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PCI-COM-8ULP User’s Guide page 31
+12V to -7V. Since any driver can be disconnected (or tristated) from the line, it must
withstand this common mode voltage range while in the tristate condition.
The following illustration shows a typical multidrop or party line network. Note that the
transmission line is terminated on both ends of the line but not at drop points in the
middle of the line.
Figure 3: Typical RS485 Two-Wire Multidrop Network
RS485 Four-Wire Multidrop Network
An RS485 network can also be connected in a four-wire mode. In a four-wire network
it's necessary that one node be a master node and all others be slaves. The network is
connected so that the master communicates to all slaves and all slaves communicate
only with the master. This has advantages in equipment that uses mixed protocol
communications. Since the slave nodes never listen to another slave's response to the
master, a slave node cannot reply incorrectly.