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Introduction into IEC 61131-1
General Information


The International Standard IEC 61131 applies to programmable controllers (PLC) and their associated peripherals such as programming and debugging tools (PADTs), Human-machine interfaces (HMIs), etc. which have as their intended use the control and command of machines and industrial processes.
PLCs and their associated peripherals are intended to be used in an industrial environment and may be provided as open or enclosed equipment. If a PLC or its associated peripherals are intended for use in other environments, then the specific requirements, standards and installation practices for those other environments must be additionally applied to the PLC and its associated peripherals.
The functionality of a programmable controller can be performed as well on a specific hardware and software platform as on a general-purpose computer or a personal computer with industrial environment features. This standard applies to any products performing the function of PLCs and/or their associated peripherals. This standard does not deal with the functional safety or other aspects of the overall automated system. PLCs, their application program and their associated peripherals are considered as components of a control system.
Since PLCs are component devices, safety considerations for the overall automated system including installation and application are beyond the scope of this standard. However, PLC safety as related to electric shock and fire hazards, electrical interference immunity and error detecting of the PLC-system operation (such as the use of parity checking, self-testing diagnostics, etc.), are addressed. Refer to IEC 60364 or applicable national/local regulations for electrical installation and guidelines.
This part of IEC 61131 gives the definitions of terms used in this standard. It identifies the principal functional characteristics of programmable controller systems.

(incl. page number)

1 Scope 13
2 Normative references 15
3 Definitions 17
4 Functional characteristics 35
4.1 Basic functional structure of a programmable controller system 35
4.2 Characteristics of the CPU function 43
4.2.1 Summary 43
4.2.2 Operating system 43
4.2.3 Memory for application data storage 44
4.2.4 Execution of the application program 44
4.3 Characteristics of the interface function to sensors and actuators 45
4.4 Characteristics of the communication function 45
4.5 Characteristics of the human-machine interface (HMI) function 46
4.6 Characteristics of the programming, debugging, monitoring, testing
and documentation functions
4.6.1 Summary 46
4.6.2 Language 46
4.6.3 Writing the application program 47
4.6.4 Automated system startup 47
4.6.5 Documentation 48
4.6.6 Application program archiving 48
4.7 Characteristics of the power supply functions 49
5 Availability and reliability 49