Omron CX-Programmer 9, Operation Manual

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PART 1: CX-Programmer
CHAPTER 4 – Reference OMRON
CX-Programmer _Page 78
on the size of the subscript, the resulting address may exceed the memory area, causing
unexpected operation.
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: Global symbols are only global for a particular PLC. It is not possible to share symbol
definitions between PLCs on the project workspace.
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.
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.
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.
Network symbol Name Data
type
Address/value
Publication Input Output
Names used in
EtherNet/IP
networks must be
within 48
characters in
length. Sets the
data type
of the
global
symbol. Sets the
address or
value of the
global symbol. Sets a
network
symbol that
can be
accessed
from
external
devices. When “input” is
selected, the
symbol will be
used as the input
tag in the
EtherNet/IP data
link (cyclic
communications). When “output” is
selected, the
symbol will be used
as the output tag in
the EtherNet/IP
data link (cyclic
communications).
Note : Network symbols can only be used with a CJ2H-CPU6
@
-EIP. In ladder diagrams, network
symbols are displayed using icons.
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… 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.