In a PLC, what is stored in the program memory?

In a Programmable Logic Controller (PLC), program memory is specifically designated for storing the actual control program, which includes the instructions and logic that dictate how the PLC operates. Constants play a vital role in this programming. They are values that do not change during the operation of the program, such as fixed numerical values used in calculations or specific settings that the program relies on to function correctly.

By storing constants in program memory, the PLC ensures that these values remain consistent and readily accessible for the execution of the programmed logic. This allows the program to maintain its functionality and reliability over time. The constants defined in the memory help in defining thresholds, limits, or reference points that are crucial for various control operations within the PLC environment.

In contrast, intermittent variables, temporary data, and real-time data are typically stored in different types of memory, such as data memory or specific registers, which are designed for dynamic data that change frequently during operation. These categories reflect aspects of the PLC's operation but do not reside in program memory as constants do.