MELSEC iQ-R/MELSEC iQ-F Structured Text (ST) Programming Guide Book

Oct 17, 2026

This guide provides safety-focused precautions for using Mitsubishi Electric MELSEC iQ-R and MELSEC iQ-F programmable controllers when programming with Structured Text (ST) in GX Works3. It explains the WARNING and CAUTION classifications and emphasizes interlock circuits, security controls against cyberattacks, and proper handling by end users. The document defines allowed operating conditions, outlines prohibited applications, and clarifies liability limitations for misuse, unauthorized access, viruses, and DoS attacks. It also advises verifying program and circuit example applicability to real systems.

LanguageEnglish

CategoryTechnology

FormatPDF

Pages112

Reading Time4 h 42 min

AccessFree to download

Safety Precautions

Conditions of Use for the Product

Introduction

Relevant Manuals

Terms

Generic Terms and Abbreviations

Part 1 ST Program

MELSEC iQ-R/MELSEC iQ-F Structured Text (ST) Programming Guide Book (Read these precautions before using this product. ) Before using this product, please read this manual and the relevant manuals carefully and pay full attention to safety to handle the product correctly. The precautions given in this manual are concerned with this product only. For the safety precautions of the programmable controller system, refer to the user's manual for the CPU module used. In this manual, the safety precautions are classified into two levels: " WARNING" and " CAUTION". | WARNING | Indicates that incorrect handling may cause hazardous conditions, resulting in death or severe injury. | | --- | --- | | CAUTION | Indicates that incorrect handling may cause hazardous conditions, resulting in minor or moderate injury or property damage. | | --- | --- | Under some circumstances, failure to observe the precautions given under " CAUTION" may lead to serious consequences. Observe the precautions of both levels because they are important for personal and system safety. Make sure that the end users read this manual and then keep the manual in a safe place for future reference. [Design Precautions] | WARNING | | --- | | ● When data change, program change , or status control are performed from a personal computer to a running programmable controller, create an interlock circuit outside the programmable controller to ensure that the whole system always operates safely. | | [Security Precautions] | | WARNING | | ● To maintain the security (confidentiality, integrity, and availability) of the programmable controller and the system against unauthorized access, denial-of-service (DoS) attacks, computer viruses, and other cyberattacks from external devices via the network, take appropriate measures such as firewalls, virtual private networks (VPNs), and antivirus solutions. | (1) MELSEC programmable controller ("the PRODUCT") shall be used in conditions; i) where any problem, fault or failure occurring in the PRODUCT, if any, shall not lead to any major or serious accident; and ii) where the backup and fail-safe function are systematically or automatically provided outside of the PRODUCT for the case of any problem, fault or failure occurring in the PRODUCT. (2) The PRODUCT has been designed and manufactured for the purpose of being used in general industries. MITSUBISHI ELECTRIC SHALL HAVE NO RESPONSIBILITY OR LIABILITY (INCLUDING, BUT NOT LIMITED TO ANY AND ALL RESPONSIBILITY OR LIABILITY BASED ON CONTRACT, WARRANTY, TORT, PRODUCT LIABILITY) FOR ANY INJURY OR DEATH TO PERSONS OR LOSS OR DAMAGE TO PROPERTY CAUSED BY the PRODUCT THAT ARE OPERATED OR USED IN APPLICATION NOT INTENDED OR EXCLUDED BY INSTRUCTIONS, PRECAUTIONS, OR WARNING CONTAINED IN MITSUBISHI ELECTRIC USER'S, INSTRUCTION AND/OR SAFETY MANUALS, TECHNICAL BULLETINS AND GUIDELINES FOR the PRODUCT. ("Prohibited Application") Prohibited Applications include, but not limited to, the use of the PRODUCT in; • Nuclear Power Plants and any other power plants operated by Power companies, and/or any other cases in which the public could be affected if any problem or fault occurs in the PRODUCT. • Railway companies or Public service purposes, and/or any other cases in which establishment of a special quality assurance system is required by the Purchaser or End User. • Aircraft or Aerospace, Medical applications, Train equipment, transport equipment such as Elevator and Escalator, Incineration and Fuel devices, Vehicles, Manned transportation, Equipment for Recreation and Amusement, and Safety devices, handling of Nuclear or Hazardous Materials or Chemicals, Mining and Drilling, and/or other applications where there is a significant risk of injury to the public or property. Notwithstanding the above restrictions, Mitsubishi Electric may in its sole discretion, authorize use of the PRODUCT in one or more of the Prohibited Applications, provided that the usage of t

FAQs

What do WARNING and CAUTION mean in this manual?

WARNING indicates incorrect handling may cause hazardous conditions resulting in death or severe injury. CAUTION indicates incorrect handling may cause hazardous conditions resulting in minor or moderate injury or property damage.

What security measures does the manual recommend for programmable controllers?

The manual recommends measures to maintain confidentiality, integrity, and availability against unauthorized access, DoS attacks, viruses, and other cyberattacks, such as using firewalls, VPNs, and antivirus solutions.

What kinds of applications are prohibited for the product?

Prohibited applications include uses in nuclear power plants and other power plants where public impact could occur, railway/public service purposes requiring special quality assurance, and high-risk environments such as aircraft/aerospace, medical applications, vehicles, and safety devices involving significant risk of injury to the public or property.

Oct 17, 2026

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