From the course: PLC Memory Organization
Rack-based systems - Ladder Logic Tutorial
From the course: PLC Memory Organization
Rack-based systems
- [Instructor] MicroLogix and SLC 500 controllers use a rack-based fixed-memory structure. As the name indicates, the memory locations are fixed. The memory space for rack-based system is divided into two broad categories; program files and data files. In RSLogix500 software, the data are saved in the highlighted area. The common memory structure for this type of system is a two-drawer filing cabinet. One drawer for program files and the second drawer for data files. The data and program file groups are also subdivided. So think about it like each drawer has certain number of files inside and the location is fixed for each file. The order matters as well. Program files, in general, contain controller information, main ladder logic program, interrupt subroutines, and all subroutine programs. In RSLogix500, there are up to 256 program files divided like this. System files and program files. The second category is data files. This is the area of the processor memory where input and output status are stored, processor status and the status of various bits and numerical data, and the same number of files, 256, are included in the data file section. They're also subdivided into instruction-specific files and file types. For example, timer and counter instruction and input and output status. So for all the controller types that use a rack-based system and use RSLogix500, these memory files will be exactly the same. The memory locations for program files in data files are fixed.
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