Creating a PLC Program

8/12/2019 Creating a PLC Program

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Creating a PLC Program

This is a simplified procedure for interface familiarisation purposes. For a PLC to function, you will

normally create a program off line (locally on your computer) then go online and transfer it into the PLC's

memory. Before you start this task, it is best to collect the following information:

Determine the PLC/CPU device type and PLC memory settings required to run your program.

Determine the type of communications connection to the PLC.

Determine the input/output requirements for your program, and organise I/O units into racks attached to your PLC.

PLC/Network Device Type Settings

Select the Newoption in the Filemenu.

A dialog box is displayed for selecting the PLC device type and connection settings. See the Change

PLC helpfor details.

The new project is created and the structure is shown in theproject workspace.

Assigning I/O Points on the PLC's Racks and Units

Select the I/O Tableof the new PLC on the project workspace.

When a PLC is first switched on it will create a real I/O tablebased on the units which are actually

plugged into its racks.

You may need to create an I/O Table model on your computer which matches the registered and real IO

table in the PLC.

When you work online you may thentransferyour created I/O Table to the PLC's registered IO Table

(not all PLCs allow this). The PLC stores the registered I/O Table separately from the real I/O Table, and

will continually check that they match.

You can compare your local I/O Table on your computer with the registered I/O Table in the selected

PLC to check if there are differences.

When an I/O assignment has been made, addresses which are within the I/O table show special prefixes

on the ladder editor. An 'I' prefix shows that the address is mapped to an input unit. A 'Q' prefix showsthat the address is mapped to an output unit. The address' usage is also shown in thesymbol tables.

Writing the Program

If you are using the mouse, ensure that you have the Diagram and Viewstool barsdisplayed.

The PLC is designed to respond to sensing (on or off) inputs to which the PLC is connected. These inputs

are graphically represented in the ladder diagram as contacts, for example , allowing you place them in

a logical sequence to control the output (a coil) from the PLC or to trigger a function such as a timer.

Programs can be structured by using Function Blocks to handle repetitive tasks. Ladder or StructuredText can be used within Function Blocks. The main programming language (and language used to call the

Function Blocks are Ladder or Structured Text).Seeladder programming


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It is necessary to insert arunginto the editor before elements (contacts, coils, or instructions) can be

placed in it

In some cases, it is not possible to show parts of a mnemonic program as a ladder rung. In these cases, a

statement list box is used for the section, and other parts of the program appear as ladder. A block

program is a special part of a program that cannot be shown in ladder form. The block program contains

logical instructions that cannot be used in the normal ladder format.

When on-line to a PLC and monitoring, it is possible to see power-flow executing. The parts of the

diagram where power is present are shown with a thick line of the power-flow colour.

CX-Programmer can show the mnemonic instructions that are produced from the ladder constructs. Themnemonics view displays these and updates the view whenever the ladder diagram is changed. It is also

write a program in mnemonic instructions and observe the changes in the ladder view.

Inserting Ladder Program Elements

Creating a PLC Program

Contact/Coil Dialogs

Instruction Dialogs PLC Instructions

Mnemonics View

For details of how the Ladder Section Window has been affected by the introduction of the IEC61131-3

support, refer to theEnhancements to Support IEC61131-3 Function Blockstopic.

Entering a Contact/Coil (Ladder Section Window)

The same dialog is used for entering both contacts and coils. It can however be displayed in two forms,

either: simple dialog mode or detailed dialog mode. The default mode can be set in theTools | Optionsdialog.

Note:The operand of a contact or coil is an address representing a bit - a BOOLdata type.

Simple dialog mode

An address or symbol name can be entered in this dialog. When Detail button is pressed, the dialog

changes to Detailed dialog mode.

If the Show with comment dialog option also ticked in theOptiondialog, then a comment dialog will

appear after entering an address or symbol name.

Inputting Symbols

Input the symbol name and click the OKButton (or press the EnterKey). The New Symbol Dialog Box

will be displayed.


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Enter the address and comment, and then click the OKButton.

The symbol can be registered in either the Global Symbol Table or Local Symbol Table. Select the check

box to register the symbol in the Global Symbol Table.

Detailed Dialog Mode

When the Detail button is pressed, the contact/coil dialog expands to include a number of additional

fields. Unchecking the Show in simple dialog mode box in theOptiondialog, will cause the contact/coil

dialog to always be shown in the detailed mode.

Name or address

This list shows all defined symbols for the program and PLC.

It is possible to just type an address in the operand list. If the address has been mapped to a symbol, the

symbol is indicated in the symbol information area.

As a name is typed, CX-Programmer attempts to complete the symbol name from those in the list. The

details of the symbol are shown in the symbol information area of the dialog. A new symbol name can

also be typed, if it is required to create a new symbol at the time of entering the contact/coil information.

Also,symbols can be filteredby symbol names or comments inputted in the dialog.


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Creating a Symbol: It is possible to create a symbol directly from within this dialog, by typing a new

name (conforming to thesymbol naming convention) or address:

When typing a new symbol name, an address and optional comment can also be entered. If the

contact/coil was previously entered using an address, the address will be filled in. The address may be left

blank, to specify that the address is to beautomatically allocated. The symbol will be created aslocal,unless the

Global check box is set.

A global symbol may belinked to a CX-Server file.

If an address is entered instead of a name, only a comment may be entered in addition. This will create a

global, unnamed symbol. If a comment is not entered, a symbol will not be created.

Edit Symbol

Press this button in order to edit an existing symbol - when pressed, the editing fields in the 'symbol

information' part of the dialog are enabled. Note that it is only possible to edit a BOOLdata-type, non

pre-defined symbolin this dialog.

Thename, address and comment may be changed. Note that the scope of the symbol (local/global)

cannot be changed. Alocal symbolmust have a name. Onlyglobal symbolscan belinked to a CX-Server

file.

When editing a symbol, the symbol information fields work in the same way as theInsert symboldialog.

Symbol Information

The name, address/value,data typeand comment of the chosen symbol is shown. The scope of the

symbol is shown as eitherglobal or local.

For CJ2H-CPU -EIP, whether the symbol is a network symbol is also shown.

Differentiation

It may be required for the contact to be differentiated, i.e. be active for one scan only.

Select differentiate up, differentiate downor none.

Note: This only applies to contacts - it is not available for coils.

Immediate Refresh

It may be required for the operand in an I/O unit to be read/written immediately upon execution of the

contact/coil. Usually, the input or output is read/written to the input/output unit at the end of the execution

cycle.


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Instruction Dialog (Ladder Section Window)

Instruction

Instruction dialog is available in the ladder view to enter details of a PLC instruction. The dialog can be

displayed in two forms, either: simple dialog modeor detailed dialog mode.The default mode can be

set in theTools | Optionsdialog.

Note:Some instructions are not available for use when programming in ladder language - they must be

used directly in amnemonic list.

Simple dialog mode

Instruction and operand(s) can be entered in this dialog. When Detailbutton is pressed, the dialog

changes to Detailed dialog mode.

If the Show with comment dialogoption is also ticked in theOptiondialog, then a comment dialog (for

each operands) will appear after entering an instruction and operand(s).

Detailed dialog mode

When the Detailbutton is pressed, the Instruction dialog expands to include a number of additional fields.

Unchecking the Show in simple dialog modebox in the Options dialog, will cause the Instruction dialog

to always be shown in the detailed mode.

There are three ways to select an instruction:


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1. Type its name into the Instruction edit box. CX-Programmer attempts to complete

the function name as it is typed, and displays details of the required operands below

the instruction edit box.

2. Type the instruction number into the Instruction edit box. Use the correct number

of digits for the PLC (some PLCs use 2 digits, the others use 3 digits). When an

instruction number has been recognised, CX-Programmer fills in the instruction

name and displays details of the required operands below the instruction edit box.

3. Select an instruction from a list by selecting the Find Instructionbutton. When theFind Instructiondialog appears, select the instruction category in the left side of the

displayed dialog then the required instruction in the category from the right side of

the dialog.

Note that it is possible to get full help on a particular instruction by typing its mnemonic into the

Instructionfield, and pressing Instruction Help. If the instruction exists on more than one family of

PLCs (i.e. C-series, CV-series, or CS/CJ-series), a choice of family will first be given.

Note than certain instructions have dependencies between operands, so that the value of one operand will

determine the valid range of another. For these instructions, it is possible to check whether the operands

are valid by pressing the Checkbutton.

Operands

The number of operands available for selection will depend on the instruction selected.

Instruction and operands should be divided with a space when entering in Simple dialog mode. To enter

operand in detailed dialog mode, use the keyboard up/down cursor, or Tab keys to select the operand

number to edit .

The valid range for the selected operand is indicated below the operand box. This updates as informationis typed. Initially (when the information for the operand is empty), it shows the address ranges which are

valid. When beginning to type the operand details, the information is updated to show the valid range for

the address type chosen.

It is possible to use asymbolfor the operand. The symbol name may be typed directly or the symbol can

be selected using the find symbol dialog. To browse for a symbol, press F3 when entering the operand, or

press the browse button to the right of the edit box.

When a symbol name or comment is input in the operand box and the [Filter symbol] button is pressed,

the[Filter Symbol] dialogis shown and the target symbol can be selected from the dialog to input it in the

[Operand] box.

Seeoperand typesfor an explanation of how to enter a correct operand.

Symbol Information

Whenever CX-Programmer finds asymbolassociated with the typed operand, symbol information is

displayed in this box. The name, address/value and comment are shown, together with thedata typeof the

symbol and its scope (global or local).

Expansion Table

You can use this table to define theexpansion instructions.


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PLC Instruction Sets

Every PLC has a set of special instructions which can be used for programming. Different types of PLC

have different abilities and this is reflected in the instructions available. Some instructions are common

across all PLCs.

PLCs can be split into 3 families - the instruction sets for each are described below:

C-Series PLC Instructions

CV-Series PLC Instructions

CS/CJ-Series PLC Instructions

Mnemonic Editing

Select the Mnemonicsoption from the View menu (or press Alt+Mkeys) to display the Mnemonics

representation of the ladder diagram (note that asectionmust be selected for this menu option to be

available). Use Alt+D to return to diagram view.

The mnemonic editor behaves in a similar way to a text editor, except that you can be in 'block' or

'editing' modes.

When starting the mnemonic editor, it opens in block mode and whole line is shown selected at the cursor

position. In this mode, it is possible to manipulate the lines of mnemonic using the copy / cut / paste and

delete options. To select more than one line at a time, select the line at the top of the desired range of

lines, hold down the shift key and click/move the cursor to the end of the range.

It is possible to paste a mnemonic program into CX-Programmer from a text-editor - the text will be

pasted in the position of the cursor.

To enter 'edit' mode, press return. In this mode, a line of text is highlighted in the text highlight colour.

The text may now be edited in a normal way. To add another line, press return. To exit 'edit' mode, press

Esc.

The mnemonic instructions available for each PLC type are described in thePLC Instruction Set

references.

Note: To synchronize the cursor in the mnemonic editor and the ladder editor, Synchronize ladder and mnemonic

cursorsoption must be checked - seeDiagram Options.

Note

The Mnemonic Editor is not available in a CS/CJ-H and CJ1M PLC's project with Function Blocks being

used.

Documents

Creating a PLC Program