Network Router User Manual

GFK-1535A Chapter 6 Redundancy 6-3
6
Using the NIU in a Genius Bus Redundancy System
In Genius bus redundancy, there are two bus cables each connected to a Bus
Controller or PCIM. I/O devices such as the NIU may be connected to either one
bus of the pair, or to both. A device that is connected to both busses actually
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 busses 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.
Redundant Bus Configurations
Many different redundant bus configurations are possible. Three basic ways of
using an NIU with a redundant bus are described below.
An NIU can be installed directly on both cables of the dual bus pair.
The
NIU is configured to operate as a bus switching device in addition to
performing its normal functions. Here, two NIUs are installed on a dual bus.
Each NIU would be set up as a bus switching device.
Bus A
Bus B
N
IU NIU