Rockwell Automation 1775-S5_SR5,D17756.5.5 User Manual PLC-3 FAMILY I/0 - Manual (Page 97)

Programming DH and DH+
Message Procedures
Chapter 6
6-6
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 (see
chapter 5).
Type Description
procedural The scanner recognizes procedural user symbols only in the procedure that
you generate it in.
interprocedural The scanner recognizes interprocedural user symbols in the procedure that
you generate it in and 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 scanner can store the contents of the user
symbol in a data field that is less than 32 bits long. Attempting to put a
data value into a field that is too small, causes the scanner to generate error
code 189 (see appendix B).
Use a system symbol as either a procedure name or a symbolic address.
You must name a system symbol following the general rules given in
“Using Symbols,” page 6-4. The character @ delimits a system symbol
and distinguishes it from a user symbols.
Symbol Type Description
procedure
names
A procedure name is a way of referring to a message procedure. You assign a
procedure name at the time you generate or edit the message procedure.
One procedure can execute a second procedure simply by stating the name of
that second procedure. This allows for nesting of procedures up to 3 levels deep.
symbolic
addresses
A symbolic address is another way of representing the logical address of data.
You can generate a symbolic address by using the CREATE command. You can
use a symbolic address for a logical address anywhere in a message procedure.
The system symbols area of memory stores all symbolic addresses.
scope of
system
symbols
System symbols can be either local or global in scope. The scanner recognizes
a global system symbol in any context. It recognizes a local system symbol only
in the operating context that the system symbol is created in. For detailed
information on context, refer to the PLCĆ3 Family Controller Programming Manual
(publication 1775Ć6.4.1).
At the time you generate the system symbol, you specify it to be local or global.
If you do not specify the scope of the system symbol, it defaults to local.
Important: Do not confuse the terms local and global symbols with local and
remote stations. Both local and global symbols have meaning only at the station
where you generate them.
Using User Symbols
Using System Symbols