FANUC Robotics America GFK-1535A - Manual (Page 83)

6-2 VersaMax™ System Genius® Network Interface Unit User's Manual – November 2000 GFK-1535A
6
CPU/Bus Controller Redundancy
In CPU redundancy, two Bus Controllers on the same bus can send control outputs
at the same time. Both Bus Controllers automatically receive inputs and fault
reports from all devices on the bus that have been configured as being in “CPU
Redundancy” mode. The Bus Controllers must use serial bus addresses 30 and 31.
VersaMax I/O Stations can be used on a bus controlled by redundant CPUs/Bus
Controllers.
Bus Controller
(Device 30)
NIU NIU NIU
Bus Controller
(Device 31)
How the two sets of outputs from the dual CPUs are handled by an NIU depends on
whether the NIU is set up for Hot Standby or Duplex redundancy, as explained
below. If the station contains any analog modules, the only form of CPU
redundancy permitted is Hot Standby.
Hot Standby CPU Redundancy
An NIU configured for Hot Standby mode is normally controlled by the Bus
Controller assigned to serial bus address 31. If no outputs are available from 31 for
three bus scans, the NIU accepts outputs from the Bus Controller assigned to serial
bus address 30. If outputs are not available from either Bus Controller, outputs go
to their configured defaults or hold their last state. In Hot Standby redundancy,
Bus Controller 31 always has priority; when it is online, it has control of the
outputs.
Duplex CPU Redundancy
An NIU configured for Duplex mode compares outputs it receives from the two bus
controllers to determine if they match. If corresponding outputs are the same, the
NIU sets the output to that state. If corresponding outputs are not the same, the NIU
sets the output to its configured ON or OFF Duplex Default State. If either bus
controller stops sending outputs to an NIU, its outputs are directly controlled by the
remaining device. Only discrete I/O modules can operate in Duplex redundancy
mode; do not use Duplex mode if the station contains any analog I/O modules.