Mitsubishi Electronics FX1S manual What is STL, SFC And IEC1131 Part 3?, General note

FX Series Programmable Controllers STL Programming 3

3.STL Programming

FX1S FX1N FX2N FX2NC

This chapter differs from the rest of the contents in this manual as it has been written with a training aspect in mind. STL/SFC programming, although having been available for many years, is still misunderstood and misrepresented. We at Mitsubishi would like to take this opportunity to try to correct this oversight as we see STL/SFC programming becoming as important as ladder style programming.

3.1What is STL, SFC And IEC1131 Part 3?

The following explanation is very brief but is designed to quickly outline the differences and similarities between STL, SFC and IEC1131 part 3.

In recent years Sequential Function Chart (or SFC) style programming (including other similar styles such as Grafcet and Funktionplan) have become very popular through out Europe and have prompted the creation of IEC1131 part 3.

The IEC1131 SFC standard has been designed to become an interchangeable programming language. The idea being that a program written to IEC1131 SFC standards on one manufacturers PLC can be easily transferred (converted) for use on a second manufacturers PLC.

STL programming is one of the basic programming instructions included in all FX PLC family members. The abbreviation STL actually means STep Ladder programming.

STL programming is a very simple concept to understand yet can provide the user with one of the most powerful programming techniques possible. The key to STL lies in its ability to allow the programmer to create an operational program which ‘flows’ and works in almost exactly the same manner as SFC. This is not a coincidence as this programming technique has been developed deliberately to achieve an easy to program and monitor system.

One of the key differences to Mitsubishi’s STL programming system is that it can be entered into a PLC in 3 formats. These are:

Ι) Instruction - a word/mnemonic entry system

ΙΙ) Ladder - a graphical program construction method using a relay logic symbols

ΙΙΙ) SFC - a flow chart style of STL program entry (similar to SFC)

Examples of these programming methods can be seen on page 2-1.

General note:

•IEC1131-3: 03.1993 Programmable controllers; part 3: programming languages. The above standard is technically identical to the ‘Euro-Norm’

EN61131-3: 07.1993

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