Popular microcontrollers execute IEC 61131-3 standard operators and functional blocks in simply automatic control tasks

摘要

Over the recent decades a common approach seems to be taken for granted that only dedicated Central Processing Unit (CPU) offered as self-contained modules by various manufacturers are the only solution for implementation of Programmable Logic Controllers (PLC). To demonstrate right the contrary authors of this study reveal various CPU solutions of PLCs developed on the basis of some typical microcontrollers, including the ones from the families MCS-51, AVR and ARM with the Cortex M3 core. These CPUs were then employed to run a control program developed in an Instruction List (IL) language that meets recommendations of the IEC-61131-3 standard. The paper demonstrates that the basic operators of the IL language can be used to simplify bodies of the standard defined function and function blocks. The rules are outlined that the authors adhered to at development of commands for the IL language with dedicated examples that explain how these commands can be used to define functionalities for operational modules of counters and timers and a combinational Boolean function — on the example of the LIMIT procedure. It is also suggested to define several new operators that additionally simplify the notation. The scope of investigations includes also comparison between the solutions suggested by stipulations of the standard in question and the own solutions proposed by the authors with presentation of the outcome from the comparison. The disclosed considerations served as the basis to suggest the new architecture for a CPU that is suitable for operation in line with rules imposed by the standard, but on the other hand it can be used for operation with some modifications suggested by the authors and intended to reduce processing time for some operators, Boolean functions and functional blocks.