The memory of a PLC is organized by type.
The memory space can be divided into two broad categories:
Program Memory
Data memory.
Advanced ladder logic functions allow controllers to perform calculations, make decisions, and do other complex tasks. Timers and counters are examples of ladder logic functions. They are more complex than basic input contacts and output coils and rely heavily upon data stored in the memory of the PLC.
A memory map can be used to show how memory is organized in a PLC .
1. Data table
● Input/output locations
● Internal relay and timer/counter locations
2. User program
The user program causes the controller to operate in a particular manner
3. Housekeeping memory
Used to carry out functions needed to make the processor operate (no access by user).
Processor memory organization refers to how a processor (CPU) manages and organizes memory for storing and accessing data and instructions. Here’s a brief overview of the typical organization:
- Registers: These are small, high-speed storage locations inside the CPU used to store data temporarily during processing. Registers are the fastest form of memory and are used to hold data that the CPU is actively processing. Registers are used for various purposes, including storing operands, holding intermediate results, and storing memory addresses.
- Cache Memory: Cache memory is a small, high-speed memory located within or close to the CPU. Its purpose is to temporarily store frequently accessed data and instructions to speed up processing. Cache memory helps reduce the time it takes to access data from the main memory (RAM) by providing faster access to frequently used data and instructions.
- Main Memory (RAM): Main memory, also known as random-access memory (RAM), is the primary memory used for storing data and instructions that are actively being used by the CPU. RAM is larger but slower compared to cache memory. It holds the operating system, application programs, and data currently in use. Data in RAM is volatile, meaning it is lost when the power is turned off.
- Secondary Storage: Secondary storage devices, such as hard disk drives (HDDs) and solid-state drives (SSDs), are used for long-term storage of data and programs. Unlike RAM, secondary storage retains data even when the power is turned off. Secondary storage is slower than RAM but offers larger storage capacities.
- Memory Hierarchy: Processor memory organization follows a hierarchy, with registers being the fastest and closest to the CPU, followed by cache memory, main memory, and secondary storage. Data is moved between these levels of memory hierarchy based on their frequency of access and the principle of locality.
- Memory Management Unit (MMU): The MMU is responsible for translating virtual addresses generated by the CPU into physical addresses in memory. It also manages memory protection, virtual memory, and memory allocation.
Overall, processor memory organization plays a crucial role in the performance and efficiency of a computer system by providing fast access to data and instructions needed for processing.