Omron CX-PROGRAMMER V9 - REV 12-2009 Operation Manual page 158

PART 1: CX-Programmer
CHAPTER 4 – Reference
Global Symbols
The PLC global symbol table is initially filled with some pre-set symbols, which depend upon the PLC type. For
example, the symbol 'P_1s' (1 second pulse) is created for many PLC types. All pre-set symbols have the prefix
'P_' and they may not be removed or edited.
A global symbol table contains the PLC's symbols – these symbols can be referenced by any program in the
PLC. Any unnamed symbols (IO comment - just addresses given a comment) are contained within the global
table - they may not be placed in a local symbol table.
Note:
Local Symbols
These symbols are specific to a particular program, and cannot be referenced by any other. It is recommended
that symbols are defined locally to a program unless the address is being used in multiple programs. This makes
the project more manageable and maintainable.
It is possible to define a symbol at a local level with the same name as a symbol at global level. This is
considered an override of the symbol definition. The program uses the symbol definition from its local level.
This is a powerful feature, but can be achieved by mistake, so CX-Programmer issues a warning when
validating symbols if this is done.
Network Symbols
Network symbols can be used to access I/O memory in the CPU Unit from external devices.
When a tag is used from an external device (e.g., host, PT, or Programming Device) to access I/O memory (e.g.,
tag data links using EtherNet/IP networks), the tag accesses I/O memory using a network symbol.
Network symbols are registered in the global symbol table. When the network symbol is registered, one of the
following attributes is selected for the network symbol: Publication, Input, or Output. Network symbols can be
used as global symbols when being used within a program in the PLC. Network symbols cannot be specified in
the local symbol table.
Name
Names used in
EtherNet/IP
networks must be
within 48
characters in
length.
Note:
Copying and Pasting Symbols
It is possible to cut, copy and paste symbols from one symbol table to another. It is also possible to move
symbols between tables by using drag/drop. Note that pre-set symbols can not be removed, but they may be
overridden.
For advanced users, it is possible to paste symbols from another application into a symbol table. This can be
done from any application that supports a text format – for example a spreadsheet. Refer to Chapter 5 -
Advanced Topics for further information.
Use the following procedure to copy or move symbols.
1, 2, 3...
CX-Programmer _Page 78
on the size of the subscript, the resulting address may exceed the memory area, causing
unexpected operation.
Global symbols are only global for a particular PLC. It is not possible to share symbol
definitions between PLCs on the project workspace.
A program's local symbol table is created empty. The local symbol table can be viewed by
selecting the View Local Symbol button from the toolbar.
Data
Address/value
type
Sets the Sets the
data type address or
of the value of the
global global symbol.
symbol.
Network symbols can only be used with a CJ2H-CPU6@-EIP. In ladder diagrams, network
symbols are displayed using icons.
1. Select a symbol, or symbols in the symbol table. More than one symbol can be selected by
pressing Shift and selecting another item to extend the selection or by pressing Ctrl and
selecting another item to add to the selection.
Network symbol
Publication Input
Sets a When "input" is
network selected, the
symbol that symbol will be
can be used as the input
accessed tag in the
from EtherNet/IP data
external link (cyclic
devices. communications).
OMRON
Output
When "output" is
selected, the
symbol will be used
as the output tag in
the EtherNet/IP
data link (cyclic
communications).