Rockwell Automation 1772-LP3 PLC - 2/30 Programmable Controller Programming and Operations Manual - Manual (Page 155)

Output Override and I/O Update Instructions
Chapter 7
7Ć13
NOTE: If a fault occurs in a local rack, all racks will behave according to
their last state switch whether dependent or independent mode has been
selected.
Independent fault zone programming is used to zone off independent
sections of user program. The programming for each I/O chassis can be
contained in separate MCR or ZCL zones or more than one I/O chassis can
be contained in a single zone (Figure 7.7). The user may also wish to
enable alternate parts of a program when a fault occurs in a remote I/O
chassis (Figure 7.8).
Independent fault zones are programmed using the appropriate fault status
bits as Examine Off conditions for the MCR or ZCL zones (Figures 7.7
and 7.8). When a fault occurs in a remote I/O chassis, the corresponding
fault status bit is set on. The MCR or ZCL zone conditioned by that fault
status bit will go false, enabling the zone. All outputs within the zone will
be controlled by the zone.
In addition to programming independent fault zones, the user must ensure
that the fault control switch on the S/D panel is set on for independent
mode. Refer to publication no. 1772-929 for the switch locations and
settings of the 1772-SD2 distribution panel.
NOTE: If a fault occurs in a local rack, all racks will behave according to
their last state switch whether dependent or independent mode has been
selected.
7.4.2
Independent Programming