EN 60848:2013

SLOVENSKI STANDARD
01-september-2013
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GRAFCET specification language for sequential function charts (IEC 60848:2013)
Entwurfssprache GRAFCET für Ablauf-Funktionspläne (IEC 60848:2013)
Langage de spécification GRAFCET pour diagrammes fonctionnels en séquence (CEI
60848:2013)
Ta slovenski standard je istoveten z: EN 60848:2013
ICS:
01.100.25 5LVEHVSRGURþMD Electrical and electronics
HOHNWURWHKQLNHLQHOHNWURQLNH engineering drawings
35.060 Jeziki, ki se uporabljajo v Languages used in
informacijski tehniki in information technology
tehnologiji
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN 60848
NORME EUROPÉENNE
June 2013
EUROPÄISCHE NORM
ICS 29.020 Supersedes EN 60848:2002

English version
GRAFCET specification language for sequential function charts
(IEC 60848:2013)
Langage de spécification GRAFCET pour GRAFCET, Spezifikationssprache für
diagrammes fonctionnels en séquence Funktionspläne der Ablaufsteuerung
(CEI 60848:2013) (IEC 60848:2013)

This European Standard was approved by CENELEC on 2013-04-03. CENELEC members are bound to comply
with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the CEN-CENELEC Management Centre or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and notified
to the CEN-CENELEC Management Centre has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus,
the Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany,
Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland,
Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Management Centre: Avenue Marnix 17, B - 1000 Brussels

© 2013 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 60848:2013 E
Foreword
The text of document 3/1135/FDIS, future edition 3 of IEC 60848, prepared by SC 3B “Documentation”
of IEC/TC 3 “Information structures, documentation and graphical symbols" was submitted to the
IEC-CENELEC parallel vote and approved by CENELEC as EN 60848:2013.

The following dates are fixed:
(dop) 2014-01-03
• latest date by which the document has
to be implemented at national level by
publication of an identical national
standard or by endorsement
• latest date by which the national (dow) 2016-04-03
standards conflicting with the
document have to be withdrawn
This document supersedes EN 60848:2002.

This edition constitutes a global technical revision with the extended definition of the concept of
variables introducing: internal variable, input variable and output variable.

Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC [and/or CEN] shall not be held responsible for identifying any or all such
patent rights.
Endorsement notice
The text of the International Standard IEC 60848:2013 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following note has to be added for the standard indicated:

IEC 61131-3:2003 NOTE Harmonised as EN 61131-3:2003 (not modified).

IEC 60848 ®
Edition 3.0 2013-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
GRAFCET specification language for sequential function charts

Langage de spécification GRAFCET pour diagrammes fonctionnels en séquence

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX XA
ICS 29.020 ISBN 978-2-83220-648-5

– 2 – 60848 © IEC:2013
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 8
3.1 Terms in the GRAFCET . 8
3.2 Terms, general purpose . 10
4 General principles . 10
4.1 Context . 10
4.2 GRAFCET, a behaviour specification language . 11
4.3 GRAFCET, short presentation . 12
4.3.1 General . 12
4.3.2 Structure . 12
4.3.3 Elements for interpretation . 12
4.4 Syntax rule . 13
4.5 Evolution rules . 14
4.5.1 General . 14
4.5.2 Initial situation . 14
4.5.3 Clearing of a transition . 14
4.5.4 Evolution of active steps . 14
4.5.5 Simultaneous evolutions . 14
4.5.6 Simultaneous activation and deactivation of a step . 14
4.6 Input events . 14
4.6.1 General . 14
4.6.2 Input events specification . 15
4.7 Internal events . 15
4.7.1 General . 15
4.7.2 Internal events described by the step activation . 15
4.7.3 Internal events described by the deactivation of a step . 15
4.7.4 Internal events described by the clearing of a transition . 15
4.8 Output modes . 16
4.8.1 General . 16
4.8.2 Continuous mode (assignation on state) . 16
4.8.3 Stored mode (allocation on event) . 16
4.9 Application of the evolution rules . 16
4.9.1 General . 16
4.9.2 Non transient evolution . 17
4.9.3 Transient evolution . 17
4.9.4 Consequence of a transient evolution on the assignations . 17
4.9.5 Consequence of a transient evolution on the allocations . 18
4.10 Comparison between the two output modes . 18
4.10.1 General . 18
4.10.2 Determination of the value of the outputs . 19
4.10.3 Analysis of the value of the outputs for a grafcet chart at a defined
instant . 19
4.10.4 Actions relative to transient evolution . 19
4.10.5 Possible conflict on the value of the outputs . 19

60848 © IEC:2013 – 3 –
5 Graphical representation of the elements . 19
6 Graphical representation of sequential structures . 32
6.1 General . 32
6.2 Basic structures . 32
6.2.1 Sequence . 32
6.2.2 Cycle of a single sequence. 32
6.2.3 Selection of sequences . 33
6.2.4 Step skip . 33
6.2.5 Backward sequence skip . 34
6.2.6 Activation of parallel sequences . 34
6.2.7 Synchronization of sequences . 34
6.2.8 Synchronization and activation of parallel sequences. 35
6.3 Particular structures. 36
6.3.1 Starting of a sequence by a source step . 36
6.3.2 End of a sequence by a pit step . 36
6.3.3 Starting of a sequence with a source transition . 37
6.3.4 End of a sequence by a pit transition . 38
7 Structuring . 38
7.1 General . 38
7.2 Partition of a grafcet chart . 38
7.2.1 Connected grafcet chart . 38
7.2.2 Partial grafcet . 39
7.3 Structuring using the forcing of a partial grafcet chart . 40
7.4 Structuring using the enclosure . 41
7.5 Structuring using the macro-steps . 43
Annex A (informative) Example of the control of a press . 45
Annex B (informative) Example: Automatic weighing-mixing . 46
Annex C (informative) Relations between GRAFCET of IEC 60848 and the SFC of
IEC 61131-3 . 52
Bibliography . 54

Figure 1 – Graphical representation of the sequential part of a system . 11
Figure 2 – Structure and interpretation elements used in a grafcet chart to describe the
behaviour of a sequential part of the system defined by its input and output variables . 13
Figure 3 – Example of grafcet with enclosures (including description) . 43
Figure A.1 – Representation of the working press using a grafcet . 45
Figure B.1 – Overview diagram of weighing-mixing system . 46
Figure B.2 – Grafcet of a weighing-mixing involving only continuous actions . 47
Figure B.3 – Grafcet of the weighing-mixing, involving continuous and stored actions . 48
Figure B.4 – Grafcet of the weighing-mixing, divided into a global description using
macro-steps and a description detailed by the macro-step expansions . 49
Figure B.5 – Structuring with operating modes using forcing orders . 50
Figure B.6 – Structuring with operating modes using enclosing step . 51

Table 1 – Steps . 20
Table 2 – Transitions . 21
Table 3 – Directed links . 22

– 4 – 60848 © IEC:2013
Table 4 – Associated transition-conditions . 23
Table 5 – Continuous actions . 27
Table 6 – Stored actions . 30
Table 7 – Comments associated with elements of a grafcet chart . 31
Table 8 – Partial grafcet chart . 39
Table 9 – Forcing of a partial grafcet chart . 40
Table 10 – Enclosing steps. 41
Table 11 – Macro-steps . 44

60848 © IEC:2013 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
GRAFCET SPECIFICATION LANGUAGE
FOR SEQUENTIAL FUNCTION CHARTS

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60848 has been prepared by the former subcommittee 3B:
Documentation, of IEC technical committee 3: Information structures, documentation and
graphical symbols.
This third edition cancels and replaces the second edition published in 2002 and constitutes a
global technical revision with the extended definition of the concept of variables introducing:
internal variable, input variable and output variable.
The text of this standard is based on the following documents:
FDIS Report on voting
3/1135/FDIS 3/1138/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.

– 6 – 60848 © IEC:2013
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until the
stability date indicated on the IEC web site under "http://webstore.iec.ch" in the data related to
the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
60848 © IEC:2013 – 7 –
INTRODUCTION
This International Standard is mainly aimed at people such as design engineers, maintenance
engineers, etc., who need to specify the behaviour of a system, e.g. the control and command
of an automation system, safety component, etc. This specification language should also serve
as a communication means between designers and users of automated systems.

– 8 – 60848 © IEC:2013
GRAFCET SPECIFICATION LANGUAGE
FOR SEQUENTIAL FUNCTION CHARTS

1 Scope
This International Standard defines the GRAFCET specification language for the functional
description of the behaviour of the sequential part of a control system.
This standard specifies the symbols and rules for the graphical representation of this language,
as well as for its interpretation.
This standard has been prepared for automated production systems of industrial applications.
However, no particular area of application is excluded.
Methods of development of a specification that makes use of GRAFCET are beyond the scope
of this standard. One method is for example the "SFC language" specified in IEC 61131-3,
which defines a set of programming languages for programmable controllers.
NOTE See Annex C for further information on the relations between IEC 60848 and implementation languages
such as the SFC of IEC 61131-3.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
(void)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
NOTE The definitions of the terms in 3.1 apply only in the context of the GRAFCET specification language.
3.1 Terms in the GRAFCET
3.1.1
action
GRAFCET language element associated with a step, indicating an activity to be performed on
output or internal variables
3.1.2
directed link
GRAFCET language element indicating the evolution paths between steps by connecting steps
to transitions and transitions to steps
3.1.3
grafcet chart
function chart using the GRAFCET specification language
___________
GRAFCET: GRAphe Fonctionnel de Commande Etape Transition.

60848 © IEC:2013 – 9 –
Note 1 to entry: The “grafcet chart” can, in short form, be called “grafcet”.
3.1.4
input event
event characterized by the change of at least one value of all input variables of the sequential
part of the system
3.1.5
internal event
event characterized by an input event associated with the situation of the sequential part of the
system
3.1.6
interpretation
part of the GRAFCET specification language enabling the linkage of:
– the input variables and the structure, by the means of the transition-condition; and
– the output variables and the structure, by the means of the actions
3.1.7
situation
state of the system described by the GRAFCET specification language and characterized by
the active steps at a given instant
3.1.8
step
GRAFCET language element used for the definition of the state of the sequential part of the
system
Note 1 to entry: A step can be active or inactive.
Note 2 to entry: The set of active steps represents the situation of the system.
3.1.9
transient evolution
evolution characterized by the clearing of several successive transitions on the occurrence of a
single input event
3.1.10
transition
GRAFCET language element indicating a possible evolution of the activity between two or more
steps
Note 1 to entry: The possible evolution is realised by clearing the transition.
3.1.11
transition-condition
GRAFCET language element associated with a transition indicating the result of a boolean
expression
Note 1 to entry: The transition-condition can be either true or false.
3.1.12
variable
scalar quantity defined by its name and Boolean, numeric value
3.1.13
input variable
variable which may influence the behaviour described by the grafcet chart

– 10 – 60848 © IEC:2013
EXAMPLE Boolean variable indicating the violation of a temperature limit.
Note 1 to entry: The variable may belong to the environment or to some other system component.
3.1.14
output variable
variable which may be influenced by the behaviour described by the grafcet chart
EXAMPLE Setpoint of a PID-controller.
Note 1 to entry: The variable may belong to the environment or to some other system component.
3.1.15
internal variable
variable used inside the grafcet chart and invisible for other system components and the
environment
EXAMPLES Step variable X* (symbol 2.1 of Table 1), step duration T* (symbol 2.2 of Table 1), loop counter within
a grafcet chart.
3.2 Terms, general purpose
3.2.1
chart
graph
graphical presentation describing the behaviour of a system, for example the relations between
two or more variable quantities, operations or states
3.2.2
structure
part of the GRAFCET specification language enabling the description of the possible evolution
between situations
3.2.3
system
set of interrelated elements considered in a defined context as a whole and separated from
their environment
Note 1 to entry: Such elements may be material objects and concepts as well as their results (e.g. forms of
organisation, mathematical methods, programming languages).
Note 2 to entry: The system is considered to be separated from the environment and from the other external
systems by an imaginary surface, which cuts the links between them and the system.
Note 3 to entry: The language GRAFCET can be used to describe the logical behaviour of any kind of system.
[SOURCE: IEC 60050-351:1998, 351-11-01]
4 General principles
4.1 Context
The implementation of an automated system requires, in particular, a description relating cause
and effect. To do this, the logical aspect of the desired behaviour of the system will be
described.
The sequential part of the system is the logical aspect of this physical system (see Figure 1).
The behaviour indicates the way in which the output variables depend on the input variables.
The object of the grafcet chart is to specify the behaviour of the sequential part of the systems.

60848 © IEC:2013 – 11 –
Environment
System
Sequential part of the system
Init
G10.y := 0 %
Start Λ [L10.x < 2 %]
Dos_R
G10.y := 100 %
Start
G10.y
[L10.x > 50 %]
L10.x
T10.a
Dos_F
G10.y := 10 %
Go_on
[L10.x > 60 %]
Heating
G10.y := 0 % T10.a
Go_on
Non-sequential part of the system
T10.y
T10.w
PID
T10.r
IEC  365/13
L10.x tank level G10.y dosing valve – position
T10.a temperature loop – automatic mode T10.w temperature loop – setpoint
T10.r temperature loop – measured value T10.y temperature loop – manipulated value
Figure 1 – Graphical representation of the sequential part of a system
4.2 GRAFCET, a behaviour specification language
The GRAFCET specification language enables a grafcet chart to be created showing the
expected behaviour of a given sequential system. This language is characterized mainly by its
graphic elements, which, associated with an alphanumerical expression of variables, provides
a synthetic representation of the behaviour, based on an indirect description of the situation of
the system.
The behaviour description on states is the following: the "monomarked" states correspond to
the situations of the grafcet chart, which implies the uniqueness of the situation at a given
instant. The states are connected to each other by means of an evolution condition, which
allows the passage from one situation to another one to be described.
For reasons of convenience, the behaviour description based on states is better replaced by a
description based on steps. In the grafcet chart several steps may be active simultaneously,
the situation being then characterized by the set of active steps at the considered moment. The
evolution of one set of steps to another is translated by one or several transitions, each
characterized by:
• its preceding steps,
• its succeeding steps,
Input
variables
Output
variables
– 12 – 60848 © IEC:2013
• its associated transition-condition.
NOTE These reasons lead to the syntax rule enforcing the alternation step-transition.
4.3 GRAFCET, short presentation
4.3.1 General
The GRAFCET specification language is used for the design of grafcet charts to provide a
graphical and synthetic representation of the sequential systems behaviour. The representation
(see Figure 2) distinguishes:
• the structure, which allows possible evolutions between the situations to be described, and
• the interpretation, which enables the relationship between input, output variables and the
structure (evolution, assignation and allocation rules are necessary to achieve this
interpretation).
Symbols related to GRAFCET elements representing steps in a process and links between the
steps are presented and exemplified in Tables 1 to 4 in Clause 5.
4.3.2 Structure
The structure comprises the following basic items:
• Step (definition: 3.1.8, symbol 1). A step is either active or inactive, the set of the active
steps of a grafcet chart at any given instant represents the situation of this grafcet chart at
this instant.
• Transition (definition: 3.1.10, symbol 7). A transition indicates that an evolution of the
activity between two or more steps may evolve. This evolution is realized by the clearing of
the transition.
• Directed link (definition: 3.1.2, symbol 10). A directed link connects one or several steps to
a transition, or a transition to one or several steps.
4.3.3 Elements for interpretation
The following elements are used for the interpretation:
• Transition-condition (definition: 3.1.11, symbol 13). Associated with each transition, the
transition-condition is a logical expression which is true or false and which is composed of
input variables and/or internal variables.
• Action (definition: 3.1.1). The action indicates, in a rectangle, what shall be done to the
output or internal variable, either by assignation (continuous action, symbol 20), or
allocation (stored action, symbol 26).

60848 © IEC:2013 – 13 –
QuickDescent
On
SEQUENTIAL Boolean
HighPosition DriftRotation
Boolean
output
PART OF A
input
SlowDescent variables
LowPosition
variables
SYSTEM
EndApproch Ascent
Input variables forming the
transition condition with the
logic operator : « AND »
Steps 1 and 2
(1)
On AND HighPosition
QuickDescent DriftRotation
Ouput variables assigned in
Directed links
(2)
EndApproch
the associated actions to
the step 2
SlowDescent DriftRotation
(3)
LowPosition Continuous actions

associated to the steps
3 and 4
4 Ascent
Transitions 3 and 4
Transition condition
(4)
HighPosition
associated to transition 4
STRUCTURE
INTERPRETATION
IEC  366/13
Figure 2 – Structure and interpretation elements used in a grafcet chart to describe the
behaviour of a sequential part of the system defined by its input and output variables
4.4 Syntax rule
Step transition and transition step alternation shall always be respected whatever the
sequence.
Consequences:
– 14 – 60848 © IEC:2013
• Two steps shall never be connected directly by a directed link;
• The directed link shall only connect a step to a transition or a transition to a step.
4.5 Evolution rules
4.5.1 General
As each situation is characterized by the set of active steps at a given instant, the grafcet
evolution rules only affect the application, on the steps, of the evolution principle between the
situations of the sequential part of the system.
4.5.2 Initial situation
The initial situation is the situation at the initial time. Therefore, it is described by the set of
steps active at this time. The choice of the situation at the initial time depends on the
methodology relating to the type of sequential part of the system considered.
Rule 1: The initial situation, chosen by the designer, is the situation at the initial time.
4.5.3 Clearing of a transition
Rule 2: A transition is said to be enabled when all immediately preceding steps linked to this
transition are active. The clearing of a transition occurs:
• when the transition is enabled, and
• when its associated transition-condition is true.
4.5.4 Evolution of active steps
Rule 3: The clearing of a transition simultaneously provokes the activation of all the
immediate succeeding steps and the deactivation of all the immediate preceding steps.
4.5.5 Simultaneous evolutions
The evolution between two active situations implies that no other intermediate situation is
possible and the change from one representation of the situation by a set of steps to another
representation is instantaneous.
Rule 4: Several transitions, which can be cleared simultaneously, are simultaneously cleared.
4.5.6 Simultaneous activation and deactivation of a step
If a step is included in the description of the preceding situation and in that of the following one,
it can therefore only remain active.
Rule 5: If during the operation, an active step is simultaneously activated and deactivated, it
remains active.
4.6 Input events
4.6.1 General
The evolution rules show that only a change in the values of the input variables may cause the
evolution of the grafcet chart. This change called "input event" shall be defined by the
preceding value and the succeeding value of all the input variables to characterise this single
event. In practice, a set of input events is specified only by the characterised state change
(rising edge or falling edge) of one or several Boolean input variables.
NOTE The rising edge of a logical variable, indicated by the sign "↑" in front of a Boolean variable, indicates that
this rising edge is only true for the change from value 0 to value 1 of the variable concerned. The falling edge of a

60848 © IEC:2013 – 15 –
logical variable noted by the sign "↓" in front of a Boolean variable, indicates that this falling edge is only true for
the change from value 1 to value 0 of the variable concerned.
It is said that "the event occurs" at the date of the change of state of the input variables which
characterize it.
4.6.2 Input events specification
The input events specification is implemented by a logical expression of one or several
characteristic variables, often in a transition-condition. More rarely, it may also directly specify
an internal event (see 4.7).
EXAMPLE 1:
↑a
The expression "↑a" describes the set of all input events for which the preceding value of the input
variable “a” is 0 and its succeeding value is 1, regardless of the value of the other input variables of the
system.
a ⋅ ↑b EXAMPLE 2:
The expression "a × ↑b" describes the set of all input events for which the succeeding value of the input
variable “a” is 1, and the preceding value of the input variable "b" is 0 and its succeeding value is 1,
regardless of the value of the other input variables of the system.
a EXAMPLE 3:
The expression "a" describes the sets of all input events for which the succeeding value of the input
variable “a” is 1, regardless of the value of the other input variables of the system.
NOTE Used in a transition-condition, this expression could lead to a transient evolution (see 3.12).
4.7 Internal events
4.7.1 General
Only certain input events could occur from a given situation. The connection between a
situation and input event, which may occur from this situation, is called internal event (see 3.6).
This notion is mainly used by the designer to condition an output allocation to a set of internal
events (see 4.8.3). The description of a set of internal events is realized by one of the following
ways.
4.7.2 Internal events described by the step activation
The step activation, noted graphically (symbol 27), describes the set of internal events each of
which has this step activation as a consequence.
4.7.3 Internal events described by the deactivation of a step
The graphically noted deactivation of a step (symbol 28) describes the set of the internal
events each of which have this step deactivation as consequence.
4.7.4 Internal events described by the clearing of a transition
The graphically noted clearing of a transition (symbol 29) describes the set of internal events
each of which have the clearing of this transition as consequence.

– 16 – 60848 © IEC:2013
4.8 Output modes
4.8.1 General
The actions enable links to establish the connection between the evolution of the grafcet chart
and the outputs. Two output modes, continuous mode or stored mode, describe how the
outputs depend on the evolution and on the system inputs.
4.8.2 Continuous mode (assignation on state)
In the continuous mode, the association of an action with a step indicates that an output
variable has a true value if the step is active and if the assignation condition is verified. The
assignation condition is a logical expression of the input variables and/or the internal ones (see
symbol 22). If one of the conditions is not met and provided that no other action relating to the
same output meets the conditions, the output variable concerned takes the false value.
Assignation refers to imposing the values of the output variables (true or false).
The set of the local assignation (relating to the active steps at a given instant) defines the
assignation of all the output variables for this situation.
Assignation rule: for a given situation, the value of the outputs relating to the continuous
actions is assigned:
• to the true value, for each output relating to the actions associated with active steps and for
which the assignation conditions are verified,
• to the false value, for the other outputs (which are not assigned to the true value).
4.8.3 Stored mode (allocation on event)
In the stored mode, the association of an action to internal events is used to indicate that an
output or internal variable takes and maintains the enforced value if one of these events
occurs.
Explicit representations are necessary to describe the association of the actions with the
events (activation step, deactivation step, clearing of a transition, etc.).
The value of an output or internal variable relating to a stored action remains unchanged until a
new specified event modifies its value.
Allocation refers to storing, at a considered moment, a determined value affected to an output
or internal variable.
Allocation rule: the value of an output or internal variable, relating to a stored action and
associated to an event, is allocated to the indicated variable, if the specified internal event
occurs; the value of this variable is false (Boolean variable) or null (numeric variable) at the
initialisation.
4.9 Application of the evolution rules
4.9.1 General
Intuitive interpretation of the evolution, called “step by step”, designates the progressive way
which allows, on the occurrence of an input event and from the preceding situation, to
determine the succeeding situation of this event, by the successive application of the evolution
rules on each transition. The interpretation facility is a device to enable an indirect specification
of the evolution, but the designer shall take care that the clearing of the transitions on this path
does not involve the effective activation of the intermediate situations.

60848 © IEC:2013 – 17 –
4.9.2 Non transient evolution
In general, the evolution is non-transient, which means that the input event only leads to one
evolution stage (the simultaneous clearing of one or more transitions).
EXAMPLE: "Non transient evolution"
Preceding situation: step 11 active, a = 0, b = 0 and c = 0.
Intuitive interpretation of the evolution:
(1)
(1)
a
a
The change in the value “a” involves the clearing of the transition (1) and the
12 activation of the step 12, the transition (2) cannot be cleared, because b = 0, the
subsequent situation is therefore: step 12 active.
b (2) b
(2)
Real interpretation of the evolution:
The occurrence of one of the input events such as the value of “a” changes from
0 to 1 leads straight to the subsequent situation: step 12 active.
(3)
(3)
c
c
4.9.3 Transient evolution
In some cases, the application of the evolution rules can lead to successively clearing some
transitions (in several evolution stages) if the transition-conditions associated with the
subsequent transitions are already true, when the first transitions considered are cleared. The
corresponding description, referred to as transient, uses the path taken to indicate how to
move from a preceding situation to a succeeding situation (see 3.9).
The corresponding intermediate steps, referred to as unstable are not activated, but we
consider that they have been "virtually" activated and deactivated along the intuitive evolution
path, as well as for the corresponding transitions which have been "virtually" cleared.
EXAMPLE: "Transient evolution"
Preceding situation: step 11 active, a = 0, b = 1 and c = 0.
Intuitive interpretation of the evolution:
The change in the value “a” involves the clearing of the transition (1) and the
virtual activation of the step 12, then the transition (2) is virtually cleared, because
b=1, leading to the succeeding situation: step 13 active.
Real interpretation of the evolution:
The occurrence of one of the input events, such as the value of "a" changes from
0 to 1, leads to the succeeding situation: step 13 active.

4.9.4 Consequence of a transient evolution on the assignations
The assignation of an output value by a continuous action associated with a step, which is an
unstable step in the case of a transient evolution, is not effective, since the step is not really
activated (see 4.8.2).
– 18 – 60848 © IEC:2013
EXAMPLE: “Co
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