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PLCs for Beginners
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If you recall from Chapter 4, computer – or in this case, PLC – memory is made of storage blocks that can have very long and complex naming conventions that are usually unreadable to humans. To remedy this, programmers will use what are known as variables or tags to provide an alias and context to memory blocks.
A variable in programming is much like a variable in mathematics. Ultimately, a variable is a placeholder for a value that may or may not be known. The only area where a programming variable will differ from a math variable is that a programming variable represents a place or location as opposed to a value, as in mathematics. This stems from its nature as an alias.
In traditional programming, these aliases are always called variables. However, in automation programming, these aliases are more often called tags, especially when working with more traditional PLC programming software. Some programmers may split hairs about the difference...