6. Redundancy with NX3030 CPU
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Principles of Operation
In this section, the redundant CPU functions using a NX3030 CPU is described, along with its
behavior and states. It’s also presented concepts and programming and configuration restrictions that
will be used in the next chapters.
NX3030 CPU Identification
A NX3030 CPU has a nonvolatile identification register where it’s possible for it to be identified as:
 Non-redundant: it can’t be used in a redundant CPU (default configuration)
ï‚· PLCA: used in the redundant CPU PLCA
ï‚· PLCB: used in the redundant CPU PLCB
The identification register can be adjusted using the MasterTool programmer. The first thing to be
done in a NX3030 CPU, before downloading the redundant project in it, is to identify it as PLCA or
PLCB. In case the identification isn’t executed, several redundancy features won’t work correctly, as,
for instance, the synchronization of the application between the PLCs.
ATTENTION:
The CPU identification register is not part of the redundant CPU project, thus it isn’t saved as part of
this project in the computer where MasterTool is being executed. The register is saved only in the
nonvolatile CPU memory.
Single Redundant Project
Due to the identification register previously described, there’s a single project for the redundant CPU,
identical for both PLCA and PLCB.
Configuration parameters that must be different for PLCA and PLCB (e.g. Ethernet interface IP
address) appear doubled in the redundant CPU project (one for the PLCA and another for the PLCB).
Each CPU will consider the correspondent one, after analyzing its identification register.
Redundant Project Structure
Redundancy Template
A redundant CPU project is created automatically from a model, called Redundancy Template.
The template starts from the minimum redundant CPU configuration, as defined in the Minimum
Configuration of a Redundant CPU section. Besides this, some dialogs with the user are made for the
insertion of additional modules in the half-clusters, such as PROFIBUS masters (NX5001) and
Ethernet modules (NX5000).
PROFIBUS remotes must be inserted by the user, below the NX5001 PROFIBUS masters already
inserted.
Furthermore, tasks and basic POUs from the program type are created, as described in the following
sections.
Single and Cyclic Task MainTask
The redundant CPU project has a single task, called MainTask, which is cyclic. The user can adjust
the task cycle time.
MainPrg Program
The MainTask is connected to a single POU from the program type, called MainPrg. The MainPrg
program is created automatically.
The MainPrg code is the following, in ST language:
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