Editing Programmable logic controller (section)

==Programming==
[[File:Ladder temporizado.svg|thumb|upright=0.9|Example of a ladder diagram logic]]

Programmable logic controllers are intended to be used by engineers without a programming background. For this reason, a graphical programming language called [[ladder logic]] was first developed. It resembles the schematic diagram of a system built with electromechanical relays and was adopted by many manufacturers and later standardized in the [[IEC 61131-3]] control systems programming standard. {{As of|2015|post=,}} it is still widely used, thanks to its simplicity.<ref name=":6">{{Harvnb|Bolton|2015|pp=16–18}}</ref>

{{As of|2015|post=,}} the majority of PLC systems adhere to the [[IEC 61131-3]] standard that defines 2 textual programming languages: [[Structured Text]] (similar to [[Pascal (programming language)|Pascal]]) and [[Instruction List]]; as well as 3 graphical languages: [[ladder logic]], [[function block diagram]] and [[sequential function chart]].<ref name=":6" /><ref>Keller, William L Jr. ''Grafcet, A Functional Chart for Sequential Processes'', 14th Annual International Programmable Controllers Conference Proceedings, 1984, p. 71-96.</ref> Instruction List was deprecated in the third edition of the standard.<ref>{{Cite web|url=https://plcopen.org/status-iec-61131-3-standard |title=Status IEC 61131-3 Standard |date=2018-07-19 |website=PLCopen |access-date=2020-04-01 }}</ref>

Modern PLCs can be programmed in a variety of ways, from the relay-derived ladder logic to programming languages such as specially adapted dialects of [[BASIC]] and [[C (programming language)|C]].<ref>{{Cite web |title=Programmable logic controller for automation systems |url=https://www.isisvarese.edu.it/wp-content/uploads/2016/03/CLIL-5B-MEC-PLC.pdf |access-date=April 8, 2024 |website=www.isisvarese.edu.it}}</ref>

While the fundamental concepts of PLC programming are common to all manufacturers, differences in [[I/O address]]ing, [[memory organization]], and [[instruction set]]s mean that PLC programs are never perfectly interchangeable between different makers. Even within the same product line of a single manufacturer, different models may not be directly compatible.<ref>{{Cite web |date=September 2020 |title=A mini view of PLC |url=https://www.researchgate.net/publication/344308053 |access-date=April 8, 2024 |website=www.researchgate.net}}</ref>

===Programming device===
Manufacturers develop programming software for their PLCs. In addition to being able to program PLCs in multiple languages, they provide common features like hardware diagnostics and maintenance, software debugging, and offline simulation.<ref name=":7" />

PLC programs are typically written in a programming device, which can take the form of a desktop console, special software on a [[personal computer]], or a handheld device.<ref name=":7">{{Harvnb|Bolton|2015|pp=19–20}}</ref> The program is then downloaded to the PLC through a cable connection or over a network. It is stored either in non-volatile [[flash memory]] or battery-backed-up [[RAM]] on the PLC. In some PLCs, the program is transferred from the programming device using a programming board that writes the program into a removable chip, such as [[EPROM]] that is then inserted into the PLC.

===Simulation===
An incorrectly programmed PLC can result in lost productivity and dangerous conditions for programmed equipment. PLC simulation is a feature often found in PLC programming software. It allows for testing and [[debugging]] early in a project's development. Testing the project in simulation improves its quality, increases the level of safety associated with equipment and can save time during the installation and commissioning of automated control applications since many scenarios can be tried and tested before the system is activated.<ref name=":7" /><ref>{{cite book |last1=Lin |first1=Sally |url=https://books.google.com/books?id=CHYlTBxqrM8C&pg=PA553 |title=Advances in Computer Science, Environment, Ecoinformatics, and Education, Part III: International Conference, CSEE 2011, Wuhan, China, August 21-22, 2011. Proceedings |last2=Huang |first2=Xiong |date=9 August 2011 |publisher=Springer Science & Business Media |isbn=9783642233449 |pages=15 |via=Google Books }}</ref>