Exploring global variable lists
In traditional programming, global variables are usually considered dangerous and bad practice. However, the philosophy in PLC programming is a little different. Global variables can be dangerous; however, it is common that many processes depend on the same values. As we’ll explore later, there are ways to encapsulate and pass data around, but when there are many different code blocks that consume the values, it can often be inefficient to pass the data around.
Global values are often placed in special files called GVLs. Variables in a GVL can be accessed and manipulated by any file. Consequently, GVLs can be kind of dangerous to use, and code that utilizes variables from a GVL can be difficult to troubleshoot. Since a variable can be altered by any block of code from any file, it can be very difficult to figure out where a defective value stems from. Also, if a value is forced, it can trigger a response in many processes. This means that it...