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GFK-1527A Chapter 5 Fault Detection 5-13
5
Bus Transmitter Module
A fault in the Bus Transmitter Module is treated just like a fault in the Redundancy
Communications Module. It is only fatal if the fault prevents communications to any expansion
racks within the system.
Failure of the Bus Transmitter Module may not easily be distinguished from a Redundancy
Communications cable failure or even an RCM failure. However, most failure modes of the Bus
Transmitter Module can be isolated to the BTM. When a Bus Transmitter Module fails, the system
responds as described for the Redundancy Communications Module and cable failure. It only faults
the PLC if the PLC has expansion racks installed.
The Bus Transmitter Module can be replaced by removing power from the rack and replacing the
module. When power is restored to the CPU, the CPU obtains synchronization with the active
system and either takes control or becomes the backup CPU.
Genius Bus Controller
In a synchronized CPU Redundancy system, all GBC faults are considered fatal. Failure of a
Genius Bus Controller is detected and isolated by the PLC. If a Genius Bus Controller fails in the
active PLC, the active PLC goes to STOP/FAULT mode and the backup assumes control.
The Genius Bus Controller can be replaced by removing power from the rack and replacing the
module. When power is restored to the CPU, the CPU obtains synchronization with the active
system and either takes control or becomes the backup CPU.
Genius Bus
For both single and dual bus Genius networks, Genius bus faults are not fatal to the PLC.
However, if a bus fault exists, it exists for both units.
Single Bus Networks Bus faults
For single bus Genius networks, there may be situations where Genius bus faults are not fatal to the
PLC. However, if a bus fault exists, it exists for both systems. There may be situations where one
controller can communicate to more blocks than the other controller can. The blocks will choose
which controller to respond to, if either can be heard.
The Genius bus can be repaired without disturbing power to either system and thus without
disturbing whichever PLC is in control of the process. Replacement of a bus can be done on line
but is not recommended because all devices on that bus will be lost until the bus is repaired.