Mitsubishi MELSEC System Q User Manual

2.2 How PLCs Process Programs
A PLC performs its tasks by executing a program that is usually developed outside the control
-
ler and then transferred to the controller’s program memory. Before you start programming it is
useful to have a basic understanding of how PLCs process these programs.
A PLC program consists of a sequence of instructions that control the functions of the control
-
ler. The PLC executes these control instructions sequentially, i.e. one after another.The entire
program sequence is cyclical, which means that it is repeated in a continuous loop. The time
required for one program repetition is referred to as the program cycle time or period.
Process image processing
The program in the PLC is not executed directly on the inputs and outputs, but on a “process
image” of the inputs and outputs:
Input process image
At the beginning of each program cycle the system polls the signal states of the inputs and
stores them in a buffer, creating a “process image” of the inputs.
2–2 MITSUBISHI ELECTRIC
How PLCs Process Programs Programmable Logic Controllers
....
....
....
Switch on PLC
Delete output memory
Input terminals
Process image
of inputs
PLC program
Process image
of outputs
Output terminals
Transfer process image
to outputs
Instruction 1
Instruction 2
Instruction 3
Instruction n
Poll inputs and signal states
and save them in the process
image of the inputs
Input signals
Output signals

Mitsubishi MELSEC System Q Specifications

General

Category	Programmable Logic Controller (PLC)
Type	Modular
Series	MELSEC
I/O Capacity	Up to 4096 points
Programming Languages	Ladder Logic, Structured Text, Function Block Diagram, Instruction List, Sequential Function Chart
Communication Protocols	Ethernet, CC-Link
Redundancy	Available in certain models
Power Supply	24 V DC, 100-240 V AC (depending on the power supply module)
Operating Temperature	0°C to 55°C
Storage Temperature	-25°C to 75°C
Humidity	5% to 95% (non-condensing)
Shock Resistance	147 m/s2 acceleration, 3 times in each of the X, Y, and Z directions
CPU Type	Various CPUs available (e.g., Q00, Q01, Q02, Q06, Q12, Q13, Q26, Q100, Q172, Q173)

Summary

2 Programmable Logic Controllers

2.2 How PLCs Process Programs

3 The MELSEC System Q

3.1 System Configuration

Details the modular structure and components of the MELSEC System Q.

3.2 Base Units

Describes available base units for mounting MELSEC System Q modules.

3.3 Power Supply Modules

Explains the function and types of power supply modules for MELSEC System Q.

3.4 The CPU Modules

Introduces different types of CPU modules available for the MELSEC System Q.

3.4.2 Memory Organisation

3.5 Digital Input and Output Modules

Describes the types and functions of digital input and output modules.

3.5.1 Digital Input Modules

Explains the specifications and considerations for digital input modules.

3.5.2 Digital Output Modules

Details the types, advantages, and specifications of digital output modules.

3.6 Special Function Modules

Introduces various special function modules for MELSEC System Q automation.

3.6.1 Analog Modules

Explains analog input and output modules and selection criteria.

3.6.2 Temperature Control Modules with PID Algorithm

3.6.3 High-Speed Counter Modules

3.6.4 Positioning Modules

3.6.5 Serial Communication Modules

3.7 Networks and Network Modules

Covers networking concepts and modules for MELSEC System Q communication.

3.7.1 Networking on all Levels

3.7.2 Open Networks

3.7.3 MELSEC Networks

3.7.4 Network Modules

Explains ETHERNET and MELSECNET modules for system communication.

4 An Introduction to Programming

4.1 Structure of a Program Instruction

4.5 Programming Languages

4.6.2 Variables

4.7 The Basic Instruction Set

Provides a reference to basic instructions used in MELSEC PLC programming.

4.7.3 Using switches and sensors

4.7.7 Pulse-triggered execution of operations

4.7.8 Setting and resetting devices

4.8 Safety First!

Emphasizes crucial safety precautions when working with PLCs and systems.

4.9 Programming PLC Applications

Demonstrates PLC application development with a practical example.

4.9.1 A rolling shutter gate

Presents a detailed example of programming a rolling shutter gate control system.

4.9.2 Programming

Guides through the process of creating a new PLC project and assigning variables.

4.9.3 The Hardware

5 Devices in Detail

5.1 Inputs and Outputs

Explains how PLC inputs and outputs connect to the controlled process.

5.1.1 External I/O Signals and I/O Numbers

5.1.2 Inputs and Outputs of the MELSEC System Q

5.2 Relays

Details the function and types of relays (normal and latched) in PLC programs.

5.3 Timers

Describes programmable internal timers, their function, and types (low/high speed, retentive).

5.4 Counters

Explains internal counters for programming counting operations and their features.

5.5 Registers

Covers registers for storing measurements and calculation results (16-bit and 32-bit).

5.5.1 Data registers

Details data registers used for memory storage in PLC programs.

5.5.3 File registers

5.7 Programming Tips for Timers and Counters

5.7.1 Specifying timer and counter setpoints indirectly

5.7.2 Switch-off delay

5.7.3 Delayed make and break

6 More Advanced Programming

6.1 Applied Instructions Reference

Provides a reference for advanced PLC instructions beyond basic logic.

6.1.1 Additional Instructions for Process CPUs

6.2 Instructions for Moving Data

Explains instructions for moving data between registers and devices.

6.2.1 Moving individual values with the MOV instruction

6.2.2 Moving groups of bit devices

6.2.3 Moving blocks of data with the BMOV instruction

6.2.4 Copying source devices to multiple destinations (FMOV)

6.2.5 Exchanging data with special function modules

Details using FROM/TO instructions for data exchange with special function modules.

6.3 Compare Instructions

Explains instructions for comparing values (numerical, string) in PLC programs.

6.4 Math Instructions

Covers basic arithmetic operations like addition, subtraction, multiplication, and division.

6.4.1 Addition

6.4.2 Subtraction

6.4.3 Multiplication

6.4.4 Division

6.4.5 Combining math instructions