| First a definition of what scope is. Scope
is the view of where the variable can be accessed. For example if
you define a variable in the VARIABLE TAG database that variable
has global scope. That means you can access that variable anywhere
in the Citect system, eg in alarms, trends, reports, cicode and all
the animation databases. This type of variable has a wide scope. If
you define a variable local to a cicode file then you can only
access that variable in that file, this variable has narrow scope.
It is good programming practice to define a variable with the
narrowest possible scope. This limits what can modify the variable
and usually the smaller the scope the faster the performance.
Citect has the following scopes for variables.
| Variable Tags
|
These tags are from the
physical plant (PLCs), DISK PLCs or Memory PLCs. They have the
widest scope of all and the slowest access time. Variables from
physical PLCs depend on the performance of the protocol. DISK PLCs
are normally much faster and Memory PLC are faster again.
|
| global cicode
|
These variables are
declared in cicode files outside of the functions. These variables
are faster than all types of variable tags and their scope is
limited to the cicode file they are declared in. These variables
are very similar to a Memory PLC while the scope is limited to a
single cicode file. These variables are faster than a memory
PLC.
|
| local cicode
|
These variables are
declared inside cicode functions. They have the narrowest scope and
are the fastest to access.
|
|
