Rockwell Automation 1775-KA PLC-3 Communication Adapter Module User Manual - Manual (Page 62)

Addressing Rules and Examples
Chapter 4
4Ć6
A symbolic address is another way of representing the logical address of
data (section titled Addresses). You can generate a symbolic address by
using the CREATE command (Chapter 8). A symbolic address can be
used anywhere that a logical address can be used in a message procedure.
The symbolic address is stored in the system symbols area of the PLC–3
memory.
Scope of System Symbols
System symbols can be either local or global in scope. A global system
symbol is known in any context. A local system symbol is known only in
the context in operation at the time the symbol was generated. Context is
explained in the PLC–3 Programming Manual (publication 1775–801).
At the time you generate the system symbol, you can specify whether it is
to be local or global. If you do not specify the scope of the system
symbol, it is assumed to be local.
Note that the terms local and global symbols should not be confused with
local and remote stations. Both local and global symbols having meaning
only at the station in which they were generated.
User Symbols
A user symbol represents a numeric value. You can generate a user
symbol and assign a value to it by means of the assignment command
(Chapter 7).
User symbols are either procedural or interprocedural. Procedural user
symbols are known only to the procedure in which they are generated.
Interprocedural user symbols are known to the procedure in which they
are generated and to any other procedure nested within that procedure.
User symbols can contain data that is up to 32 bits long. If the high–order
bits are insignificant (that is, if they can be truncated without changing the
value of the data), then the contents of the user symbol can be stored in a
data field that is less than 32 bits long. Attempting to put a data value into
a field that is too small for it will generate an error code of 189 (Appendix
B).