PACSystems VersaMax Genius Network Interface User Manual Section 6
GFK-1535D Jan 2023
Redundancy 109
6.2 Using the NIU in a Genius Bus Redundancy
System
In Genius bus redundancy, there are two bus cables each connected to a
host PLC or computer. I/O devices such as the NIU may be connected to
either one bus of the pair, or both. A device that is connected to both
buses communicates on only one bus at a time. Before the alternate bus
can be used for communications, a bus switchover must occur, and the
device must “log in” with the Bus Controller(s) on the alternate bus.
The NIU contains a built-in bus-switching relay that is used to switch
buses in a dual bus system. Other types of devices with this capability are
Field Control BIUs, Bus Switching Modules, and Series 90-70 Remote I/O
Scanner modules. These are the only types of devices that can be directly
connected to both redundant bus cables.
An NIU cannot be used as the BSM Controller for a bus stub. Other
devices cannot be located on a stub downstream of an NIU.
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