FAQ - Frequently Asked Questions
1. What's the advantage on to use, for programming of PLC systems, the Linguagem de Comandos Elétricos (Electric Commands Language) - LCE, conversely to program visually, drawing directly in the ladder diagram or in function blocks diagram?
The principal advantage is the easiness of programming, maintenance and management of the obtained PLC control programs, in proportion they are getting more and more complex. Kept in mind the right sense of proportion, this facility is similar to one obtained with the use of silicon compilers (for example, by way VHDL - Very High Speed Integrated Circuit Hardware Description Language) conversely drawing straightly digital electronic circuits.
Another positive point is the aggregation of semantics or textual significance to the control programs in LCE, with the proper text of source program constituting its better documentation, adding meaning and structure that are difficult to attain into any diagram: imagine yourself on the telephone, attempting to transmit by way of speech a ladder diagram with a lot of complexity ...
On any medium that, by technical impracticability, or matters on economy of resources, we need to transmit, store or work a PLC program into form of pure text, the alternative is the list of instructions languages - IL (Instruction List), adaptation of traditional programming language, as Basic, C, Pascal, etc., (into Structured Text - ST), or use of dedicated and specific high-level languages.
The IL languages are low-level, as the assembly, with all problems of semantics, legibility, expressively and understanding associated to all low-level languages.
In other hand, the traditional languages attend to general purposes at programming of the computers, they aren't fitting very perfectly to the specific needs and requirements of the codification of control programs. Dedicated and specific high-level languages for PLC systems, like LCE, intend supply this lacuna.See, too, Help file about LCE, for complement of the broached questions here.
2. Is there some study outline or tutorial step-by-step about the SimuPLC and the LCE?
Unfortunately, considering that I work alone on this project, I didn't get time to prepare study outline and tutorial step-by-step for teaching the employment of the program, yet.
However, in the help file of the program are described the functioning of the Simulator and of all commands of the languages used in the SimuPLC (both LCE and IL); on several commands are described small excerpts of control programs illustrating its utilization, what also can aid to understand its way programming.
In addition, various demonstrative control programs into LCE and IL are provided, placed in the folder "Exemplos" at the moment of the installation of the SimuPLC. The study of these source codes would be also too helpful on the apprenticeship of its programming mode.
3. Is it possible the ladder programming in the SimuPLC?
The entitled ladder programming is, in the reality, the straight drawing of the program control into ladder diagram, a representative scheme of the panel of relays that would be utilized if relays were used in the implementation of the program control.
The ladder programming isn't, according to widespread confusion, a programming language but a codifying way. Observe that the PLC-based systems do not store directly the ladder diagram drawn, but the derived program which is generated from the drawing, generally into Instruction List - IL - this one really the true utilized programming language. When necessary, from such code stored into IL, it is generated (or recuperated) the correspondent diagram.
I didn't implement still such way of codification, by ladder programming, in the SimuPLC, though it's a facility which I will try implement into future version.
Observe, however, that one of the my proposals, according to answer to the question 1, is that the programming of PLCs by high-level languages is more productive that the straight drawing on diagrams, mainly into larger size projects, that become still naturally documented by the source into high-level code.
Nevertheless, to reach such objectives it's necessary that the user have attainments at programming with this type of language; if he does not have experience at programming into other high-level languages, would be desirable that he/she had studied a little of logic and construction of algorithms, subjects of numberless books and web sites easily found.
4. Would can the SimuPLC control real I/O points directly, by PC ports, functioning as a "SoftPLC"?
The SimuPLC aims at help apprenticeship of PLCs programming by way simulation, as well the introduction of a new language, the Linguagem de Comandos Elétricos – LCE (Electric Commands Language).
Since the version 4.0.0, however, the SimuPLC project was broaden to “SoftPLC” area, controlling actual I/O points by way of serial cables connected to external hardwares to linking from their I/O points to Ports COM from PC (with serial communication protocol RS-232C), using even USB-to-Serial cables if the PC does not have available Port COM. And the version 4.1.0 broaden the possibilities of SoftPLC functionalities with communication by way of Port LPT1.
Obs.: notice, however, that the proper simulation in itself can be considered the virtual functioning as a “SoftPLC”, moreover when interconnected virtually to simulated sensors and actuators of the virtual plants implemented on the Simulator.
Copyright © 2002
André Luiz Barbosa
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