14.2 PROGRAM VS VARIABLE MEMORY

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The memory in a PLC is divided into program and variable memory. The program memory contains the instructions to be executed and cannot be changed while the PLC is running. (Note: some PLCs allow on-line editing to make minor program changes while a program is running.) The variable memory is changed while the PLC is running. In ControlLogix the memory is defined using variable names (also called tags and aliases).