Introduction

IEC conforming sequential control is created from SFC sections (top level), transition sections and action sections.

SFC sections are only permitted in the projects master task. SFC sections can not be used in other tasks or DFBs.

Each SFC section contains one or more SFC networks (sequences).

Structure of an SFC section

Zero or more actions belong to every step. A transition condition belongs to every transition.

The last transition of the sequence is always connected to the first step of the sequence (using a graphical link or jump label). Step sequences run cyclically.

Properties of an SFC program

Properties of an SFC program:

  • SFC section always have a grid background.

  • Because of performance reasons, it is strongly recommended to create less than 100 SFC sections in a project (macro section are not counted).

  • An SFC section contains a maximum of 200 lines and 64 columns.

  • SFC objects can theoretically be placed in every unoccupied cell.

  • Steps, transitions and jumps each require a cell. Branches and joints do not require their own cell, but are inserted into the respective cell of the step or transition. Text objects can be placed anywhere in the window.

  • Steps and transitions are linked with one another through directional links. Two steps can never be directly linked, and must always be separated by a transition, see also section Connection rules in the Reference manual.

  • To prevent step sequences being subdivided, 99 linked steps with the transitions are vertically displayed along with a locking jump with its transition.

  • A maximum of 1024 steps can be placed per SFC section (including all their macro sections).

  • A maximum of 100 steps can be active per SFC section (including all their macro sections) (multi token), see also Tools > Project Settings dialog box, Language extensions tab, Sequential Function Chart (SFC) area.

  • A maximum of 64 steps can be set simultaneously per SFC section (multi token), see also Tools > Project Settings dialog box, Language extensions tab, Sequential Function Chart (SFC) area.

  • A maximum of 100 actions are permitted using the S qualifier per SFC Section.

  • A maximum of 20 actions can be assigned to each SFC step.

  • The processes of the active signal status take place along the directional links, triggered by the connecting of a transition. The direction of the string process follows the directional links and runs from the under side of the predecessor step to the top side of the successive step. Branches are processed from left to right.

  • A syntax and semantics check is performed immediately after the statement is entered. The result of this check is displayed in colored text.

  • Syntactically or semantically incorrect sections can be saved.

SFC program objects

The objects of the programming language SFC (Sequential Function Chart) help to divide a section into a number of:

These objects can be linked with each other using links.

Comments for the logic of the program can be added using text objects.

Edit and view functions

Edit and view functions of the SFC editor:

Online functions

Online functions of the SFC editor:

SFC save and restore

The SFC_RESTORE function block is used to restart all SFC charts of an application with a given set of active steps at a state, saved before a CPU failure.

In a recovery situation it is possible to set a group of steps that represent a given state in the process and to continue at that point.

(See SFC_RESTORE: SFC Save and Restore in the System Library).