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4-17GFK-0787B Chapter 4 PLC Subsystem
Output Processing
For outputs, the PLC does not perform “redundancy” voting. Instead, voting is done by
the specified types of discrete output block groups. Analog blocks do not provide
redundancy voting or autotest features. Both discrete and analog Genius blocks can be
used in the output subsystem as non-GMR blocks, however.
Discrete Outputs
As it does for inputs, the GMR software uses separate areas of the Output Table for non-voted
outputs, fault-tolerant outputs and copies of the fault-tolerant outputs.
After the application program executes, the GMR software processes discrete output
data as described below.
The application program places outputs into the discrete Output Table. Data for blocks
that are included in the GMR configuration is placed at the start of the output table. In
the illustration below, the application program outputs for redundant blocks are labelled
“logic outputs”. This data is followed by outputs for non-voted blocks.
The GMR software copies these logic output into the bottom portion of the Output Table.
This data, shown as Fault-tolerant Outputs in the illustration below, is used for physical
outputs for the blocks. This separation of physical outputs from logical outputs prevents
disruption of outputs such as latches and seal circuits during autotesting.
During the output scan portion of the CPU sweep, the CPU sends the non-voted outputs
plus the copied fault-tolerant outputs to the Genius blocks.
Discrete Output Table
Logic Outputs
Available for
Simplex Outputs
Fault-tolerant Outputs
Reserved memory
GMR
Logic
Application
Program
Fault-tolerant
Output
Devices
Non-voted
Outputs