Features, advantages, and differentiators of the CPP Library
The CPP Library stores data that will survive a power-cycle, reset, new download, or equipment change; or can be used in a production run. The CPP Library is often used for Parameters, Persistent variables, and Recipes.
CPP-managed variables are automatically registered when a Function Block is instantiated. There are no persistence or recipe lists to create or maintain. Just add an instance of a Function Block and its CPP variables are automatically managed in one or more CSV files in the runtime file system. If more instances of Function Blocks are added to the design, their variables are automatically managed by the CPP Library. No further user effort is required.
The CPP Library will create the initial CSV file containing the default values for all the CPP variables, in all the instances of Function Blocks that implement the CPP Library. This saves the user from the laborious and error-prone task of hand-typing this file.
Since the CPP stores its variable values in well-organized human-readable ASCII files rather than binary files, the CPP files can be easily modified if persistence, parameter, or recipe variables values are added or removed from Function Blocks, or instances of Function Blocks are added or removed. Being able to modify the files allows the CPP persistence values to be moved to systems which are not identical to the originating system. Of course, at any time the user can have the CPP write a new CSV file which will include all the variables or instances, as described in the previous bullet. The CPP Library provides the maximum possible flexibility so your data is easily reused and is never lost.
Parameters are set for all configurable objects from a consolidated source file which is easily managed in any spreadsheet software. There is no need to manually traverse the device tree searching for and opening each instance individually to set its parameters. Plus the parameters can be set either offline or online. In addition, the CPP Library does not have hierarchy restrictions like the built-in parameter tool – it works with nested Function Blocks to any size and shape of hierarchy.
Product variations can be accommodated by placing different sets of parameter values in different parameter files. The proper file can be selected on startup based on the identification of the product. This same feature can be used to save and restore different recipes in a file format that is much more convenient than the built-in recipe tool.
Parameter values are stored in a human readable and editable file, not buried and inaccessible in the project file. These files may be stored in the project device tree if desired so its variable values are automatically downloaded to the target on login. Or, the files can also be copied directly to the target so the CODESYS IDE is not required in a mass production environment.
The CPP Library does not require copying values to and from a global variable list on each process cycle. So it is much more CPU efficient than the built-in persistence feature.
The CPP can initiate a file read or write from the same Task where the file action is executed (the variables will thenall be atomic), or the initiation can be in a different task from the execution (the file I/O will not pause the Task).
Variables can all be managed in the same CSV file, or sets of variables can be partitioned to be managed in different CSV files (useful to differentiate between one-time system configuration variables, operating mode variables set by the operator via a visualization, and persistent process variables).
The CPP can save all the variables in a Group for all the instances of Function Blocks, or it can save the variable values for one instance at a time. This is useful for saving the tuning parameters on an instance by instance basis.
Object-based programming has become the standard in worldwide IT software programming and is rapidly being adopted into PLC programming. To see the benefits of object-based programming and examples of how this looks in the world of industrial controls programming, please view these videos and articles:
https://www.youtube.com/watch?v=PkJYQeIUmIM
https://www.youtube.com/watch?v=vRGaW4L762k
https://www.controleng.com/articles/leverage-object-oriented-industrial-programming/
The object of object-based programming is for objects (Function Blocks) to be fully self-contained and self-reliant. When an instance of an object is declared, that instance should then automatically handle all the services it needs. The traditional programing technique of creating and maintaining separate persistent variable lists, alarm lists, log lists, and parameter lists does not scale well to today’s large and complex PLC programs.
The native CODESYS IDE lacks support for Object Oriented Programming in several areas:
Alarms
Logging/Trending
Object Oriented I/O
Persistent Variables
Parameters and Configurations
Recipes
The ControlSphere OOA library addresses issue number 1 and this ControlSphere CPP Library addresses issues 4, 5 and 6. A prototype is available for issue number 3 and a solution for issue number 2 is in the plans. Contact ControlSphere Engineering for more details.
The CPP Library is available in a low-cost, unlimited, node-locked version (and with significant quantity discounts). A single-site unlimited source-code license is also available which is not node locked. Contact sales@controlsphere.pro for more details.
The following graphics describe the format of the CPP files, shows a typical CPP file, and shows the implementation of the base class, interfaces, and methods necessary for a Function Block to gain support of the CPP Library.
Figure 1: CPP CSV File Format
The next graphics shows a CPP file for an actual design. The CPP Library initially creates this file with all the default variable values for every instance of every Function Block that implements the CPP interface. The user can then edit the values that need to be different than the initial values, and read the file back into the system to update the runtime values. Or, these values can be set during runtime (such as from a Visualization or a persistence program variable) and written again into storage that will survive a power-cycle, new download, or equipment change.
Figure 2: Typical CPP file, courtesy Marine Hydraulics
For a Function Block to gain access to the CPP Library services, the Function Block must EXTENDS the CCP EquipmentBaseClass and IMPLEMENTS the CPP PersistInt Interface. The PersistInt Methods must then be implemented to manage the values and names of the parameter, persistence, and recipe variables.
The next graphic demonstrates the coding for a single Persistence group. However, the CPP Library also supports multiple groups so that different sets of variables can be managed in different CSV files. This is typically useful to separate one-time configuration variables (which are set by the system programmer) and persistent variables (which are often set by the operator through a visualization screen), and process variables (which must survive a download or equipment change).
Figure 3: Typical Function Block Declaration and Methods
