What is PLC Memory Addressing: Simple Explanation and Example

PLC memory addressing is the method used to locate and access specific data or control points inside a Programmable Logic Controller using addresses. These addresses represent inputs, outputs, timers, counters, and internal memory locations that the PLC reads or writes to during operation.

How It Works

Think of PLC memory addressing like a street address system for a city. Each house (memory location) has a unique address so the mailman (PLC processor) knows exactly where to deliver or pick up information. In a PLC, memory addresses point to specific inputs, outputs, or internal data like timers and counters.

The PLC uses these addresses to read sensor states or write commands to devices. For example, an input address might represent a button press, while an output address controls a motor. Internal memory addresses store temporary data the PLC uses to make decisions.

This system helps the PLC organize and quickly access all the information it needs to control machines efficiently.

Example

This simple example shows how a PLC program might use memory addresses to turn on a motor when a start button is pressed.

structured_text

(* PLC Structured Text Example *)
(* I:1/0 is input address for Start Button *)
(* O:2/0 is output address for Motor *)

IF I:1/0 THEN
    O:2/0 := TRUE;
ELSE
    O:2/0 := FALSE;
END_IF;

Output

When input I:1/0 (Start Button) is TRUE, output O:2/0 (Motor) turns ON; otherwise, it turns OFF.

When to Use

PLC memory addressing is used anytime you program a PLC to control machines or processes. It is essential for linking physical devices like sensors and motors to the PLC's logic. Use memory addressing to read inputs, control outputs, and manage internal data like timers or counters.

For example, in a factory, you use memory addresses to monitor conveyor belt sensors and start or stop motors based on those sensors. In building automation, you address temperature sensors and control heating or cooling systems.

Key Points

• Memory addressing assigns unique locations to inputs, outputs, and internal data in a PLC.
• It allows the PLC to read sensor states and control devices accurately.
• Addresses are often shown as codes like I:1/0 (input) or O:2/0 (output).
• Understanding addressing is crucial for writing effective PLC programs.

Key Takeaways

PLC memory addressing identifies where inputs, outputs, and data are stored inside the PLC.

Each device or data point has a unique address the PLC uses to read or write information.

Memory addressing is fundamental for connecting physical devices to PLC logic.

Knowing how to use addresses helps you write clear and effective PLC programs.