Rockwell Automation 1772-LP3 PLC - 2/30 Programmable Controller Programming and Operations Manual - Manual (Page 154)

Output Override and I/O Update Instructions
Chapter 7
7Ć12
Each fault status bit within a group of four corresponds to two consecutive
module groups of 32 I/O points (Table 7.B). When a fault occurs in a
remote rack, one or more of the four status bits are set on depending on the
configuration of the I/O rack.
Figure 7.6
Dependent Fault Zone Programming
| / |
03
( MCR )
125
( MCR )
| / |
17
125
| / |
16
125
| / |
15
125
| / |
14
125
| / |
13
125
| / |
11
125
Entire user program
End
Dependent programming for I/O configuration in Figure 7.5
When a fault status bit is set on, the MCR or ZCL zone is false and all outputs are controlled by the zone.
In Figure 7.5, rack 1 is a local 128-I/O rack. Rack 2 consists of a 128-I/O
chassis. Rack 3 consists of four 32-I/O chassis and rack 4 consists of two
64-I/O chassis.
If a fault occurs in rack 2, all four status bits (bits 125/00
8
–125/03
8
) will be
set on. If a fault occurs in the first I/O chassis of rack 3, bit 125/17
8
will
be set on. Similarly, if a fault occurs in the first I/O chassis of rack 4, bits
125/13
8
and 125/12
8
will be set on.
By selecting either dependent or independent fault zone programming, the
user can disable certain parts of the program or the entire program when a
fault occurs in a remote I/O rack. Alternate parts of the program can also
be enabled when a fault occurs.
Dependent fault zone programming is used to disable the entire program
when a fault occurs in one remote I/O chassis. The entire user program is
zoned off using an MCR or ZCL zone (Figure 7.6). The appropriate fault
status bits for the remote I/O chassis are programmed as Examine Off
conditions for the zone. When a fault occurs in a remote I/O chassis, the
corresponding fault status bit is set on, causing the MCR or ZCL zone to
go false. All outputs will then be controlled by the MCR or ZCL zone,
including outputs of local I/O racks.
In addition to programming a dependent fault zone, the user must ensure
that the fault control switch on the 1772-SD2 distribution panel is set off
for dependent mode. Refer to publication no. 1772-929 for the switch
locations and settings on the panel.
7.4.1
Dependent Programming