Mitsubishi Digital Electronics FX2N Manual

A SERVICE OF

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STL Programming 3

3-1

3. STL Programming

This chapter differs from the rest of the contents in this manual as it has been written with a

trainin

g

aspect in mind. STL/SFC pro

g

rammin

g

, althou

g

h havin

g

been available for man

y

y

ears, is still misunderstood and misrepresented. We at Mitsubishi would like to take this

opportunit

y

to tr

y

to correct this oversi

g

ht as we see STL/SFC pro

g

rammin

g

becomin

g

as

important as ladder st

y

le pro

g

rammin

g

.

3.1 What is STL, SFC And IEC1131 Part 3?

The followin

g

explanation is ver

y

brief but is desi

g

ned to quickl

y

outline the differences and

similarities between STL, SFC and IEC1131 part 3.

In recent

y

ears Sequential Function Chart (or SFC) st

y

le pro

g

rammin

g

(includin

g

other similar

st

y

les such as Grafcet and Funktionplan) have become ver

y

popular throu

g

h out Europe and

have prompted the creation of IEC1131 part 3.

The IEC1131 SFC standard has been desi

g

ned to become an interchan

g

eable pro

g

rammin

g

lan

g

ua

g

e. The idea bein

g

that a pro

g

ram written to IEC1131 SFC standards on one

manufacturers PLC can be easil

y

transferred (converted) for use on a second manufacturers

PLC.

STL pro

g

rammin

g

is one of the basic pro

g

rammin

g

instructions included in all FX PLC famil

y

members. The abbreviation STL actuall

y

means STep Ladder pro

g

rammin

g

.

STL pro

g

rammin

g

is a ver

y

simple concept to understand

y

et can provide the user with one of

the most powerful pro

g

rammin

g

techniques possible. The ke

y

to STL lies in its abilit

y

to allow

the pro

g

rammer to create an operational pro

g

ram which ‘flows’ and works in almost exactl

y

the

same manner as SFC. This is not a coincidence as this pro

g

rammin

g

technique has been

developed deliberatel

y

to achieve an eas

y

to pro

g

ram and monitor s

y

stem.

One of the ke

y

differences to Mitsubishi’s STL pro

g

rammin

g

s

y

stem is that it can be entered

into a PLC in 3 formats. These are:

Ι

) Instruction - a word/mnemonic entr

y

s

y

stem

ΙΙ

) Ladder - a

g

raphical pro

g

ram construction method usin

g

a rela

y

lo

g

ic s

y

mbols

ΙΙΙ

) SFC - a flow chart st

y

le of STL pro

g

ram entr

y

(similar to SFC)

Examples of these pro

g

rammin

g

methods can be seen on pa

g

e 2-1.

General note:

• IEC1131-3: 03.1993 Pro

g

rammable controllers; part 3: pro

g

rammin

g

lan

g

ua

g

es.

The above standard is technicall

y

identical to the ‘Euro-Norm’

EN61131-3: 07.1993

FX Series Programmable Controllers