Iec 61131-3 Second edition 2003-01 Programmable controllers – Part 3: Programming languages

2.4.2 Initialization
When a configuration element (resource or configuration) is “started” as defined in 1.4.1, each of the
variables associated with the configuration element and its programs can take on one of the following
initial values:
- the value the variable had when the configuration element was “stopped” (a retained value);
- a user-specified initial value;
- the default initial value for the variable's associated data type.
The user can declare that a variable is to be retentive by using the RETAIN qualifier specified in
table 16 a), when this feature is supported by the implementation.
The initial value of a variable upon starting of its associated configuration element shall be determined
according to the following rules:
1) If the starting operation is a “warm restart” as defined in IEC 61131-1, the initial values of retentive
variables shall be their retained values as defined above.
2) If the operation is a “cold restart” as defined in IEC 61131-1, the initial values of retentive variables
shall be the user-specified initial values, or the default value, as defined in 2.3.3.2, for the
associated data type of any variable for which no initial value is specified by the user.
3) Non-retained variables shall be initialized to the user-specified initial values, or to the default value,
as defined in 2.3.3.2, for the associated data type of any variable for which no initial value is
specified by the user.
4) Variables which represent inputs of the programmable controller system as defined in IEC 61131-1
shall be initialized in an implementation-dependent manner.
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61131-3 
 IEC:2003(E)
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