Inst ToolsInst ToolsInst Tools
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Erection & Commissioning
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
  • Request
Search
  • Books
  • Software
  • Projects
  • Process
  • Tools
  • Basics
  • Formula
  • Power Plant
  • Root Cause Analysis
  • Electrical Basics
  • Animation
  • Standards
  • 4-20 mA Course
  • Siemens PLC Course
Reading: Types of PLC Memory
Share
Notification Show More
Font ResizerAa
Inst ToolsInst Tools
Font ResizerAa
  • Courses
  • Design
  • PLC
  • Interview
  • Control System
Search
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Erection & Commissioning
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
  • Request
Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Inst Tools > Blog > PLC Tutorials > Types of PLC Memory

Types of PLC Memory

In this post, we will learn the basic types and concepts of memory in a programmable logic controller (PLC).

Last updated: September 28, 2022 4:13 pm
Viral Nagda
PLC Tutorials
No Comments
Share
5 Min Read
SHARE

In this post, we will learn the basic types and concepts of memory in a programmable logic controller (PLC).

Contents
PLC MemoryRandom Access Memory in PLCRead Only Memory in PLC

PLC Memory

The memory of a PLC consists of two types:

  1. RAM and
  2. ROM.

Let us study the two types in detail.

Types of PLC Memory

Random Access Memory in PLC

A RAM (Random Access Memory) is that part of memory where programs and data are stored. All the user programs and data variables are stored in RAM memory. That means a RAM memory location can be written and read.

Simply, if you write a program section or create a new memory (data) variable, it is stored in RAM memory. Any changes by the programmer in the program or data will automatically be overwritten in the memory.

All the instructions and program sections are written in program RAM memory. All the IO values and variables are stored in data RAM memory.

RAM memory can further be categorized into volatile and non-volatile. Volatile memory can be defined as non-retentive memory. That means, when the PLC is powered off, the memory value is not retained.

For example, if the last value of the memory variable was 20, then after power recycles, its value will become zero. Non-volatile memory retains the value of memory even after power recycle.

Read Only Memory in PLC

ROM (Read Only Memory) refers to that part of the memory where data can only be read and not written. The operating system, firmware version, and system-defined variables are stored in ROM or EEPROM.

Now, let us see some other concepts related to PLC memory.

PLC’s also have cache memory, as like laptops, mobiles, and other storage devices. Here, the cache memory can store periodic and event tasks, system use data, and programs.

Apart from standard program memory, there is also non-program memory stored in PLC like project properties, symbols, comments, animation tables, etc.

In some PLCs, you have the option to define variables or data memory as retentive or non-retentive. For retentive memory variables, you just have to choose which variables to retain. There are some limitations set for using this part of memory.

For example, in Siemens S7-200 Smart PLCs, you get the option to choose the memory range for retentive variables. Variables out of this memory range will be automatically defined as non-retentive.

Memory backup and restore options are given in PLC for saving and restoring values of memory variables.

For example, if you click the memory backup button in a PLC software online, the values of all the data and program variables will be saved to an external file; like excel or notepad. Then, if you click the memory restore button, the values that you have saved will be overwritten in the values of variables.

The capacity of memory is defined in kilobytes. As you know, one byte is a group of 8 bits. In the memory part, thus, 1K means 1024 bytes. So, 32K memory means 32* 1024 (32768 bytes) of memory.  

Various PLC manufacturers design the memory allocation according to their requirements. Also, some provide a very dynamic allocation of memory to programmers. That means you can set the memory allocation in a PLC according to your needs.

If you liked this article, then please subscribe to our YouTube Channel for Instrumentation, Electrical, PLC, and SCADA video tutorials.

You can also follow us on Facebook and Twitter to receive daily updates.

Read Next:

  • Statement List Language
  • PLC Simulator using Excel
  • DC Injection Braking in VFD
  • What is Alarm Prioritization?
  • PLC System Cabinet Check List
Don't Miss Our Updates
Be the first to get exclusive content straight to your email.
We promise not to spam you. You can unsubscribe at any time.
Invalid email address
You've successfully subscribed !

Continue Reading

PLC Timer Instructions
How Engineers Effectively do Problem-solve and Troubleshoot?
Different Types of Schneider PLC
Workstation Healthiness Checks
PLC Timers Program
Traffic Lights Ladder Diagram using Timers
Share This Article
Facebook Whatsapp Whatsapp LinkedIn Copy Link
Share
Leave a Comment

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Stay Connected

128.3kFollowersLike
69.1kFollowersFollow
210kSubscribersSubscribe
38kFollowersFollow

Categories

Explore More

PLC Raw Count Calculation for Pressure Transmitter
Normally-Closed Contacts for Stop Buttons
Example of PLC Programming based on Logic Circuit
How to Control VFD with PLC using Ladder Logic
Working Principle of Single Phase Preventer Relay
Siemens S7-300 CPU Suffix Explanation
How to Design a System Architecture in Industrial Automation?
#3 PLC Best Practices – Leave Operational Logic in the PLC wherever feasible

Keep Learning

Comparison of Control Loops - Open, Closed, Cascade, Feedforward, Ratio

Comparison of Control Loops – Open, Closed, Cascade, Feedforward, Ratio

Static and Temp Variables in PLC

Static and Temp Variables in PLC

Principle of Operation of PLC

Principle of Operation of PLC

LogixPro Simulator Software

Introducing PLC Programming using LogixPro Simulator Software

PLC Controlling a Motor

PLC Motor Control Ladder Logic Programming

Shift Bit Register in PLC

Shift Bit Register in PLC

how-a-plc-do-the-scaling-for-a-sensor

How a PLC do the Scaling for a Sensor ?

PLC-Complete-Training-Package

Free PLC Training Software Download

Learn More

Control valve characteristics

Valve Characteristics – Quick Opening, Linear & Equal Percentage

Valve Pneumatic Actuator

What is a Pneumatic Actuator ?

VFD circuit

AC Motor Braking

Power Systems Questions & Answers

Power Systems MCQ Series 8

PLC Cabinet

PLC Programming Videos

PV Tracking in PID Controllers

What is PV Tracking ?

Ionization Transducers Objective Questions

Ionization Transducers Objective Questions

Free Electronics Software Download

Menu

  • About
  • Privacy Policy
  • Copyright

Quick Links

  • Learn PLC
  • Helping Hand
  • Part Time Job

YouTube Subscribe

Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Welcome Back!

Sign in to your account

Username or Email Address
Password

Lost your password?