YOKOGAWA STARDOM FCN-500, Engineering Manual

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<9. Advanced Engineering >
158
TI 34P02K35-02E May 31, 2017-00
LogicA
Worksheet A1
Worksheet A2
Worksheet A3
Local
variables
accessible
LogicC
Worksheet
Local
variables
accessible
LogicB
Worksheet
Local
variables
accessible
Main
Worksheet
Local
variables
accessible
Global
variables
accessible
accessible
accessible
accessible
TIP
In Logic Designer, local variables have type “VAR”, while global variables have type "VAR_EXTERNAL"
or "VAR_GLOBAL." "VAR_EXTERNAL” and “VAR_GLOBAL” are just different type names having the
meaning.
Logical POUs can have local variables defined with the same name. For instance, in the above
example, local variable V001 can be defined in LogicA, while another local variable with the same
name V001 can be defined in LogicB.
● Precautions When Defining Variables
Up to 15,000 global variables can be defined within one resource. So long as this
limit is not exceeded, the system allows a global variable to be defined even if it is in
fact used only within one specific logical POU and should really be defined as a
local variable.
Defining a global variable that really need not be a global variable does not cause a
system problem but may lead to confusion in engineering and control application
bugs. To avoid this, do not define a variable as a global variable for no good reason.
Rather, define a variable as a global variable only when necessary.
SEE ALSO
Section 4.1.6, “Application Size”