Delta DVP-PLC User Manual

PLC

PLC

DVP-PLC Application Manual

Programming

Table of Contents

Chapter 1 Basic Principles of PLC Ladder Diagram

Foreword: Background and Functions of PLC..........................................................		1	-1
1.1	The Working Principles of Ladder Diagram ........................................................	1	-1
1.2	Differences Between Traditional Ladder Diagram and PLC Ladder Diagram ........	1	-2
1.3	Edition Explanation of Ladder Diagram .............................................................	1	-3
1.4	How to Edit Ladder Diagram .............................................................................	1-8
1.5	The Conversion of PLC Command and Each Diagram Structure .........................	1	-12
1.6	Simplified Ladder Diagram ...............................................................................	1	-15
1.7	Basic Program Designing Examples..................................................................	1	-17

Chapter 2 Functions of Devices in DVP-PLC

2.1 All Devices in DVP-PLC....................................................................................		2	-1
2.2	Values, Constants [K] / [H] ...............................................................................	2	-6
2.3	Numbering and Functions of External Input/Output Contacts [X] / [Y]..................	2	-8
2.4	Numbering and Functions of Auxiliary Relays [M] ..............................................	2	-11
2.5	Numbering and Functions of Step Relays [S] .....................................................	2	-11
2.6	Numbering and Functions of Timers [T] .............................................................	2-12
2.7	Numbering and Functions of Counters [C] .........................................................	2-14
2.8	Numbering and Functions of Registers [D], [E], [F] ............................................	2	-28
2.8.1 Data register [D] ........................................................................................		2	-28
2.8.2 Index Register [E], [F] ................................................................................		2	-29
2.8.3 Functions and Features of File Registers ....................................................		2-30
2.9	Pointer [N], Pointer [P], Interruption Pointer [I] ..................................................	2-30
2.10 Special Auxiliary Relays and Special Data Registers ........................................		2	-33
2.11 Functions of Special Auxiliary Relays and Special Registers.............................		2	-69
2.12 Error Codes ...................................................................................................		2	-125

Chapter 3 Basic Instructions

3.1	Basic Instructions and Step Ladder Instructions ................................................	3-1
3.2	Explanations on Basic Instructions ...................................................................	3-3

Chapter 4 Step Ladder Instructions

4.1	Step Ladder Instructions [STL], [RET] ...............................................................	4	-1
4.2	Sequential Function Chart (SFC) ......................................................................	4	-2
4.3	How does a Step Ladder Instruction Work? .......................................................	4	-3
4.4	Things to Note for Designing a Step Ladder Program.........................................	4	-7
4.5	Types of Sequences .........................................................................................	4-9
4.6	IST Instruction .................................................................................................	4	-17

Chapter 5 Categories & Use of Application Instructions

5.1	List of Instructions ...........................................................................................	5-1
5.2	Composition of Application Instruction ..............................................................	5	-6
5.3	Handling of Numeric Values..............................................................................	5	-11
5.4	E, F Index Register Modification .......................................................................	5	-14
5.5	Instruction Index ..............................................................................................	5-16

Chapter 6 Application Instructions API 00-49

●	API00 09 Loop Control ..........................................................................		6	-1
●	API10 19	Transmission Comparison .......................................................	6-18
●	API20 29	Four Arithmetic Operation .......................................................	6-32
●	API30 39	Rotation & Displacement.........................................................	6	-46
●	API40 49	Data Processing .....................................................................	6	-57

Chapter 7 Application Instructions API 50-99

●	API50 59	High Speed Processing...........................................................	7	-1
●	API60 69	Handy Instructions..................................................................	7	-39
●	API70 79	Display of External Settings ....................................................	7-59
●	API80 88	Serial I/O ...............................................................................	7	-80

Chapter 8 Application Instructions API 100-149

●	API100 109	Communication ...................................................................	8-1
●	API110 119 Floating Point Operation ......................................................		8-23
●	API120 129	Floating Point Operation .....................................................	8-31
●	API130 139	Floating Point Operatio .......................................................	8-43
●	API140 149	Others ................................................................................	8-55

Chapter 9 Application Instructions API 150-199

●	API150 154	Others ................................................................................	9-1
●	API155 159	Position Control ..................................................................	9-14

●	API160 169 Real Time Calendar ............................................................		9-39
●	API170 171	Gray Code Conversion ........................................................	9-49
●	API172 175	Floating Point Operation .....................................................	9-51
●	API180 190	Matrix.................................................................................	9-59
●	API191 199	Positioning Instruction ........................................................	9-76

Chapter 10 Application Instructions API 215-246

●	API202 203	Others................................................................................	10	-1
●	API215 223	Contact Type Logic Operation Instruction.............................	10-7
●	API224 246	Contact Type Compare Instruction .......................................	10	-10

1 Basic Principles of PLC Ladder Diagram

Foreword: Background and Functions of PLC

PLC (Programmable Logic Controller) is an electronic device, previously called “sequence controller”. In 1978, NEMA (National Electrical Manufacture Association) in the United States officially named it as “programmable logic controller”. PLC reads the status of the external input devices, e.g. keypad, sensor, switch and pulses, and execute by the microprocessor logic, sequential, timing, counting and arithmetic operations according the status of the input signals as well as the pre-written program stored in the PLC. The generated output signals are sent to output devices as the switch of a relay, electromagnetic valve, motor drive, control of a machine or operation of a procedure for the purpose of machine automation or processing procedure. The peripheral devices (e.g. personal computer/handheld programming panel) can easily edit or modify the program and monitor the device and conduct on-site program maintenance and adjustment. The widely used language in designing a PLC program is the ladder diagram.

With the development of the electronic technology and wider applications of PLC in the industry, for example in position control and the network function of PLC, the input/output signals of PLC include DI (digital input), AI (analog input), PI (pulse input), NI (numeric input), DO (digital output), AO (analog output), and PO (pulse output). Therefore, PLC will still stand important in the industrial automation field in the future.

1.1The Working Principles of Ladder Diagram

The ladder diagram was a diagram language for automation developed in the WWII period, which is the oldest and most widely adopted language in automation. In the initial stage, there were only A (normally open) contact, B (normally closed) contact, output coil, timer and counter…the sort of basic devices on the ladder diagram (see the power panel that is still used today). After the invention of PLC, the devices displayable on the ladder diagram are added with differential contact, latched coil and the application commands which were not in a traditional power panel, for example the addition, subtraction, multiplication and division operations.

The working principles of the traditional ladder diagram and PLC ladder diagram are basically the same. The only difference is that the symbols on the traditional ladder diagram are more similar to its original form, and PLC ladder diagram adopts the symbols that are easy to recognize and shown on computer or data sheets. In terms of the logic of the ladder diagram, there are combination logic and sequential logic.

1.Combination Logic

Examples of traditional ladder diagram and PLC ladder diagram for combination logic:

Traditional Ladder Diagram			PLC Ladder Diagram
X0		Y0	X0
				Y0
X1
		Y1	X1	Y1
X2	X4	Y2	X2	X4
				Y2
X3			X3

Row 1: Using a normally open (NO) switch X0 (“A” switch or “A" contact). When X0 is not pressed, the contact will be open loop (Off), so Y0 will be Off. When X0 is pressed, the contact will be On, so Y0 will be On.

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1 Basic Principles of PLC Ladder Diagram

Row 2: Using a normally closed (NC) switch X1 (“B” switch or “B” contact). When X1 is not pressed, the contact will be On, so Y1 will be On. When X1 is pressed, the contact will be open loop (Off), so Y1 will be Off.

Row 3: The combination logic of more than one input devices. Output Y2 will be On when X2 is not pressed or X3 and X4 are pressed.

2.Sequential Logic

Sequential logic is a circuit with "draw back” structure, i.e. the output result of the circuit will be drawn back as an input criterion. Therefore, under the same input criteria, different previous status or action sequence will follow by different output results.

Examples of traditional ladder diagram and PLC ladder diagram for sequential logic:

Traditional Ladder Diagram

PLC Ladder Diagram

X5

X6

Y3

X5

X6

Y3

Y3

Y3

When the circuit is first connected to the power, though X6 is On, X5 is Off, so Y3 will be Off. After X5 is pressed, Y3 will be On. Once Y3 is On, even X5 is released (Off), Y3 can still keep its action because of the draw back (i.e.

	the self-retained circuit). The actions are illustrated in the table below.
	Device status	X5	X6	Y3
	Action sequence
	1	No action	No action	Off
	2	Action	No action	On
	3	No action	No action	On
	4	No action	Action	Off
	5	No action	No action	Off

From the table above, we can see that in different sequence, the same input status can result in different output results. For example, switch X5 and X6 of action sequence 1 and 3 do not act, but Y3 is Off in sequence 1 and On in sequence 3. Y3 output status will then be drawn back as input (the so-called “draw back”), making the circuit being able to perform sequential control, which is the main feature of the ladder diagram circuit. Here we only explain contact A, contact B and the output coil. Other devices are applicable to the same method. See Chapter 3 “Basic instructions” for more details.

1.2 Differences Between Traditional Ladder Diagram and PLC Ladder Diagram

Though the principles of traditional ladder diagram and PLC ladder diagram are the same, in fact, PLC adopts microcomputer to simulate the motions of the traditional ladder diagram, i.e. scan-check status of all the input devices and output coil and calculate to generate the same output results as those from the traditional ladder diagram based on the logics of the ladder diagram. Due to that there is only one microcomputer, we can only check the program of the ladder diagram one by one and calculate the output results according to the program and the I/O status before the cyclic process of sending the results to the output interface Æ re-reading of the input status Æ calculation Æ output. The time spent in the cyclic process is called the “scan time” and the time can be longer with the expansion of the program. The scan time can cause delay from the input detection to output response of the PLC. The longer the delay,

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1 Basic Principles of PLC Ladder Diagram

the bigger the error is to the control. The control may even be out of control. In this case, you have to choose a PLC with faster scan speed. Therefore, the scan speed is an important specification requirement in a PLC. Owing to the advancement in microcomputer and ASIC (IC for special purpose), there has been great improvement in the scan speed of PLC nowadays. See the figure below for the scan of the PLC ladder diagram program.

The output result is calculated based on the ladder diagram. (The result has not yet sent to the external output point, but the internal device will perform an immediate output.)

Read input status from outside

X0

X1

Start

Y0

Y0

X3

X10

M100

Executing in cycles

Y1

:

:

X100 M505

Y126

End

Send the result to the output point

Besides the difference in the scan time, PLC ladder and traditional ladder diagram also differ in “reverse current”. For example, in the traditional ladder diagram illustrated below, when X0, X1, X4 and X6 are On and others are Off, Y0 output on the circuit will be On as the dotted line goes. However, the PLC ladder diagram program is scanned from up to down and left to right. Under the same input circumstances, the PLC ladder diagram editing tool WPLSoft will be able to detect the errors occurring in the ladder diagram.

Reverse current of traditional ladder diagram

Reverse current of PLC ladder diagram

X0

X1

X2

Y0

X0

X1

X2

Y0

Y0

X3

X4

X5

a

b

X3 a

X4

b

X5

X6

X6

Error detected in the third row

1.3How to Edit Ladder Diagram

Ladder diagram is a diagram language frequently applied in automation. The ladder diagram is composed of the symbols of electric control circuit. The completion of the ladder diagram by the ladder diagram editor is the completion of the PLC program design. The control flow illustrated by diagram makes the flow more straightforward and acceptable for the technicians of who are familiar with the electric control circuit. Many basic symbols and actions in

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1 Basic Principles of PLC Ladder Diagram

the ladder diagram come from the frequently-seen electromechanical devices, e.g. buttons, switches, relay, timer and counter, etc. in the traditional power panel for automation control.

Internal devices in the PLC: The types and quantity of the devices in the PLC vary in different brand names. Though the internal devices in the PLC adopts the names, e.g. transistor, coil, contact and so on, in the traditional electric control circuit, these physical devices do not actually exist inside the PLC. There are only the corresponding basic units (1 bit) inside the memory of the PLC. When the bit is “1”, the coil will be On, and when the bit is “0”, the coil will be Off. The normally open contact (NO or contact A) directly reads the value of the corresponding bit. The normally close contact (NC or contact B) reads the opposite state of the value of the corresponding bit. Many relays will occupy many bits. 8 bits equal a “byte”. 2 bytes construct a “word” and 2 words combined is “double word”. Byte, word or double words are used when many relays are processed (e.g. addition/subtraction, displacement) at the same time. The other two devices, timer and counter, in the PLC have coil, timer value and counter value and they have to process some values in byte, word or double word.

All kinds of internal devices in the value storage area in the PLC occupy their fixed amount of storage units. When you use these devices, you are actually read the contents stored in the form of bit, byte or word.

Introductions on the basic internal devices in the PLC (See Ch 2. Functions of Devices in DVP-PLC for more details.)

Device	Functions
	The input relay is an internal memory (storage) unit in the PLC corresponding to a external
	input point and is used for connecting to the external input switches and receiving external
	input signals. The input relay will be driven by the external input signals which make it “0” or
	“1". Program designing cannot modify the status of the relay, i.e. it cannot re-write the basic
	unit of a relay, nor can it force On/Off of the relay by HPP/WPLSoft. SA/SX/SC/EH/EH2/SV
	series MPU can simulate input relay X and force On/Off of the relay. But the status of the
Input relay	external input points will be updated and disabled, i.e. the external input signals will not be read
	into their corresponding memories inside PLC, but only the input points on the MPU. The input
	points on the extension modules will still operate normally. There are no limitations on the times
	of using contact A and contact B of the input relay. The input relays without corresponding input
	signals can only be left unused and cannot be used for other purposes.
	& Device indication: X0, X1,…X7, X10, X11,… are indicated as X and numbered in octal
	form. The No. of input points are marked on MPU and extension modules.
	The output relay is an internal memory (storage) unit in the PLC corresponding to a external
	output point and is used for connecting to the external load. The output relay will be driven by
	the contact of an input relay, contacts of other internal devices and the contacts on itself. A
	normally open contact of the output relay is connected to the external load. Same as the input
Output relay	contacts, there are no limitations on the times of using other contacts of the output relay. The
	output relay without corresponding output signals can only be left unused and can be used as
	input relay if necessary.
	& Device indication: Y0, Y1,…Y7, Y10, Y11,…are indicated as Y and numbered in octal
	form. The No. of output points are marked on MPU and extension modules.

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Internal relay

Step

Timer

Counter

Data register

The internal relay does not have connection with the external. It is an auxiliary relay inside the PLC with the functions same as those of the auxiliary (middle) relay in the electric control circuit. Every internal relay corresponds to a basic internal storage unit and can be driven by the contacts of the input relay, contacts of the output relay and the contacts of other internal devices. There are no limitations on the times of using the contacts of the internal relay and there will be no output from the internal relay, but from the output point.

&Device indication: M0, M1,…, M4095 are indicated as M and numbered in decimal form.

DVP series PLC offers a step-type control program input method. STL instruction controls the transfer of step S, which makes it easy for the writing of the control program. If you do not use any step program in the control program, step S can be used as a internal relay M as well as an alarm point.

&Device indication: S0, S1,…S1023 are indicated as S and numbered in decimal form.

The timer is used for timing and has coil, contact and register in it. When the coil is On and the estimated time is reached, its contact will be enabled (contact A closed, contact B open). Every timer has its fixed timing period (unit: 1ms/10ms/100ms). Once the coil is Off, the contact iwlwl be disabled (contact A open, contact B closed) and the present value on the timer will become “0”.

&Device indication: T0, T1,…,T255 are indicated as T and numbered in decimal form. Different No. refers to different timing period.

The counter is used for counting. Before using the counter, you have to give the counter a set value (i.e. the number of pulses for counting). There are coil, contact and registers in the counter. When the coil goes from Off to On, the counter will regard it as an input of 1 pulse and the present value on the counter will plus “1”. We offer 16-bit and 32-bit high-speed counters for our users.

&Device indication: C0, C1,…,C255 are indicated as C and numbered in decimal form.

Data processing and value operations always occur when the PLC conducts all kinds of sequential control, timing and counting. The data register is used for storing the values or all kinds of parameters. Every register is able to store a word (16-bit binary value). Double words will occupy 2 adjacent data registers.

&Device indication: D0, D1,…,D9,999 are indicated as D and numbered in decimal form.

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1 Basic Principles of PLC Ladder Diagram

The file register is used for storing the data or all kinds of parameters when the data registers required for processing the data and value operations are insufficient. Every file register is able to store a 16-bit word. Double words will occupy 2 adjacent file registers. In SA/SX/SC series

MPU, there are 1,600 file registers. In EH/EH2/SV series MPU, there are 10,000 file registers.

File register

There is not an actual device No. for a file register. The reading and writing of file registers should be executed by instructions API 148 MEMR, API 149 MEMW, or through the peripheral device HPP02 and WPLSoft.

&Device indication: K0 ~ K9,999, numbered in decimal form.

E and F index registers are 16-bit data registers as other data registers. They can be read and

written and can be used in word devices, bit devices or as a constant for index indication.

Index register

&Device indication: E0 ~ E7, F0 ~ F7 are indicated as E and F and numbered in decimal form.

The structure of a ladder diagram:

Structure

Explanation

Instruction

Normally open, contact A

LD

Normally closed, contact B

LDI

Normally open in series

AND

connection

Normally closed in series

ANI

connection

Normally open in parallel

OR

connection

Normally closed in parallel

ORI

connection

Rising-edge trigger switch

LDP

Falling-edge trigger switch

LDF

Rising-edge trigger in series

ANDP

connection

Falling-edge trigger in series

ANDF

connection

Rising-edge trigger in parallel

ORP

connection

Falling-edge trigger in parallel

ORF

connection

Devices Used

X, Y, M, S, T, C X, Y, M, S, T, C X, Y, M, S, T, C X, Y, M, S, T, C

X, Y, M, S, T, C

X, Y, M, S, T, C

X, Y, M, S, T, C X, Y, M, S, T, C X, Y, M, S, T, C X, Y, M, S, T, C

X, Y, M, S, T, C

X, Y, M, S, T, C

								Block in series connection	ANB	-
								Block in parallel connection	ORB	-

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1 Basic Principles of PLC Ladder Diagram

			Structure							Explanation	Instruction
											MPS
										Multiple output	MRD
											MPP
										Coil driven output instruction	OUT
		S								Step ladder	STL
										Basic instruction	Application
										Application instruction	instructions
										Inverse logic	INV

Devices Used

-

Y, M, S

S

See Ch.3 for basic instructions (RST/SET and CNT/TMR) and Ch.5 ~ 10 for application instructions

-

Block:

A block is a series or parallel operation composed of more than 2 devices. There are series block and parallel block.

Series block

Parallel block

Separation line and combination line:

The vertical line is used for separating the devices. For the devices on the left, the vertical line is a combination line, indicating that there are at least 2 rows of circuits on the left connected with the vertical line. For the devices on the right, the vertical line is a separation line, indicating that there are at least 2 rows of circuits interconnected on the right side of the vertical line).

1 2

Combination line for block 1	Combination line for block 2
Separation line for block 2

Network:

A complete block network is composed of devices and all kinds of blocks. The blocks or devices connectable by a vertical line or continuous line belong to the same network.

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1 Basic Principles of PLC Ladder Diagram

Network 1

An independent network

Network 2

An incomplete network

1.4 How to Edit a PLC Ladder Diagram

The editing of the program should start from the left power line and ends at the right power line, a row after another. The drawing of the right power line will be omitted if edited from WPLSoft. A row can have maximum 11 contacts on it. If 11 is not enough, you can continuously connect more devices and the continuous number will be generated automatically. The same input points can be used repeatedly. See the figure below:

X0 X1 X2 X3 X4 X5 X6 X7 X10 C0 C1

																								00000
			X11 X12 X13
00000																									Y0

Continuous number

The operation of the ladder diagram program is scanning from top left to bottom right. The coil and the operation frame of the application instruction belong to the output side in the program and are placed in the right if the ladder diagram. Take the figure below for example, we will step by step explain the process of a ladder diagram. The numbers in the black circles indicate the order.

X0

X1

Y1

X4

Y1

M0

T0

M3

T0

K10

M1

TMR

X3

The order of the instructions:
1	LD	X0
2	OR	M0
3	AND	X1
4	LD	X3
	AND	M1

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1 Basic Principles of PLC Ladder Diagram

	ORB
5	LD	Y1
	AND	X4
6	LD	T0
	AND	M3
	ORB
7	ANB
8	OUT	Y1
	TMR	T0	K10

Explanations on the basic structures in the ladder diagram:

1. LD (LDI) instruction: Given in the start of a block.

LD instruction

LD instruction

AND block

OR block

The structure of LDP and LDF instructions are the same as that of LD instruction, and the two only differ in their actions. LDP and LDF instructions only act at the rising edge or falling edge when the contact is On, as shown in the figure below.

Rising edge

Falling edge

X0

X0

Time

Time

OFF ON

OFF

OFF ON

OFF

2. AND (ANI) instruction: A single device connects to another single device or a block in series

AND instruction						AND instruction

The structure of ANDP and ANDF instructions are the same. ANDP and ANDF instructions only act at the rising edge or falling edge.

3. OR (ORI) instruction: A single device connects to another single device or a block

OR instruction OR instruction

OR instruction

The structure of ORP and ORF instructions are the same. ORP and ORF instructions only act at the rising edge or falling edge.

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1 Basic Principles of PLC Ladder Diagram

4. ANB instruction: A block connects to a device or another block in series

ANB instruction

5. ORB instruction: A block connects to a device or another block in parallel

ORB instruction

If the ANB and ORB operations are with several blocks, the operation should be performed from up to down or left to right, combining into a block or network.

6. MPS, MRD, MPP instructions: Bifurcation point of multiple outputs, for generating many and diverse outputs. MPS instruction is the start of the bifurcation point. The bifurcation point is the intersection of the horizontal line

and vertical line. We will have to determine whether to give a contact memory instruction by the contact status of the same vertical line. Basically, every contact can be given a memory instruction, but considering the convenience of operating the PLC and the limitation on its capacity, some parts in the ladder diagram will be omitted during the conversion. We can determine the type of contact memory instruction by the structure of the ladder diagram. MPS is recognized as “┬” and the instruction can be given continuously for 8 times.

MRD instruction is used for reading the memory of the bifurcation point. Due to that the same vertical line is of the same logic status, in order to continue analyzing other ladder diagrams, we have to read the status of the original contact again. MRD is recognized as “├”.

MPP instruction is used for reading the start status of the top bifurcation point and popping it out from the stack. Since MPP is the last item on the vertical line, the vertical line ends at this point.

MPP is recognized as “└”. Using the method given above for the analysis cannot be wrong. However, sometimes the compiling program will ignore the same output status, as shown in the figure.

MPS

MPS

MRD

MPP

MPP

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7. STL instruction: Used for designing the syntax of the sequential function chart (SFC).

STL instruction allows the program designer a clearer and readable picture of the sequence of the program as when they draw a sequence chart. From the figure below, we can see clearly the sequence to be planned. When the step S moves to the next step, the original S will be “Off". Such a sequence can then be converted into a PLC ladder diagram and called “step ladder diagram”.

	M1002	M1002
		SET	S0

S0

S SET S21

S21

S SET S22

S22

S S0

RET

8. RET instruction: Placed after the completed step ladder diagram.

RET also has be placed after STL instruction. See the example below.

S20		X1
S							RET
S20		X1
S							RET

See step ladder instructions [STL], [RET] in Ch. 4 for the structure of the ladder diagram.

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1 Basic Principles of PLC Ladder Diagram

1.5The Conversion of PLC Command and Each Diagram Structure

Ladder Diagram
X0	X2	X1	Y0
X1	M0		C0
			SET	S0
	M1
M2	Y0
S0	X10
S			Y10
			SET	S10
S10	X11
S			Y11
			SET	S11
			SET	S12
			SET	S13
S11	X12
S			Y12
			SET	S20
S20	S12	S13	X13
S	S	S	S0
			RET
X0			CNT	C0
C0	X1		M0
	X1		M1
	M2
			M2
			RST	C0
			END

	LD	X0	OR
	OR	X1	block
	LD	X2	OR
	OR	M0
			block
	ORI	M1	Series
	ANB
			connection blcok
	LD	M2	AND
	AND	Y0	block
	ORB		Parallel
		X1	connection block
	AN I		ANI	The output will continue
	OUT	Y0
			Multiple	following the status of
	AND	C0
	SET	S0	outputs
	STL	S0	Step ladder Start
	LD	X10	Status S0 and X10 operation
	OUT	Y10	Status working item and
	SET	S10	step point transfer
	STL	S10	Withdraw S10 status
	LD	X11	Withdraw X11 status
	OUT	Y11
	SET	S11	Status working item and
	SET	S12	step point transfer
	SET	S13	Withdraw S11 status
	STL	S11
	LD	X12	Withdraw X12 status
	OUT	Y12	Status working item and
	SET	S20	step point transfer
	STL	S20	Bifurcation
	STL	S12
			convergence
	STL	S13
					End of step ladder
	LD	X13	Status working item
	OUT	S0	and step point transfer
	RET		Return
K10	LD	X0
	CNT	C0 K10
	LD	C0	Read C0
	MPS
	AND	X1
	OUT	M0
	MRD		Multiple
	AN I	X1
			outputs
	OUT	M1
	MPP
	AN I	M2
	OUT	M2
	RST	C0	End of program
	END

Fuzzy Syntax

The correct ladder diagram analysis and combination should be conducted from up to down and left to right. However, without adopting this principle, some instructions can make the same ladder diagram.

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1 Basic Principles of PLC Ladder Diagram

Example Program 1

See the ladder diagram below. There are 2 ways to indicate the ladder by instruction programs with the same result.

X0

X2

X4

Ideal way

Less ideal way

LD

X0

LD

X0

X1

X3

X5

OR

X1

OR

X1

LD

X2

LD

X2

OR

X3

OR

X3

ANB

LD

X4

LD

X4

OR

X5

OR

X5

ANB

ANB

ANB

The two instruction programs will be converted into the same ladder diagram. The difference between the ideal one and less ideal one is the operation done by the MPU. For the ideal way, the combination is done block by block whereas the less idea way combines all the blocks combine with one another in the last step. Though the length of the program codes of the two ways are equal, the combination done in the last step (by ANB instruction, but ANB cannot be used continuously for more than 8 times) will have to store up the previous calculation results in advance. In our case, there are only two blocks combined and the MPU allows such kind of combination. However, once the number of blocks exceed the range that the MPU allows, problems will occur. Therefore, the best way is to execute the block combination instruction after a block is made, which will also make the logic sequence planned by the programmer more in order.

Example Program 2

See the ladder diagram below. There are 2 ways to indicate the ladder by instruction programs with the same result.

	X0						Ideal way		Less ideal way
						LD		X0	LD	X0
						OR		X1	LD	X1
	X1
						OR		X2	LD	X2
	X2
						OR		X3	LD	X3
	X3								ORB
									ORB
									ORB
In this example, the program codes and the operation memory in the MPU increase in the less ideal way.
Therefore, it is better that you edit the program following the defined sequence.
Incorrect Ladder Diagram

PLC processes the diagram program from up to down and left to right. Though we can use all kinds of ladder symbols to combine into various ladder diagrams, when we draw a ladder diagram, we will have to start the diagram from the left power line and end it at the right power line (In WPLSoft ladder diagram editing area, the right power line is omitted), from left to right horizontally, one row after another from up to down. See bellows for the frequently seen incorrect diagrams:

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1 Basic Principles of PLC Ladder Diagram

OR operation upward is not allowed.

“Reverse flow” exists in the signal circuit from the beginning of input to output.

Reverse flow

The up-right corner should output first.

Combining or editing should be done from the up-left to the bottom-right. The dotted-lined area should be moved up.

Parallel operation with empty device is not allowed.

Empty device cannot do operations with other devices.

No device in the middle block.

Devices and blocks in series should be horizontally aligned.

Label P0 should be in the first row of a complete network.

Blocks connected in series should be aligned with the upmost horizontal line.

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1 Basic Principles of PLC Ladder Diagram

1.6Simplified Ladder Diagram

When a series block is connected to a parallel block in series, place the block in the front to omit ANB instruction.

X0 X1

X2

Ø

X1 X0

X2

Ladder diagram complied into instruction

LD	X0
LD	X1
OR	X2
ANB

Ladder diagram complied into instruction

LD	X1
OR	X2
AND	X0

When a single device is connected to a block in parallel, place the block on top to omit ORB instruction.

T0

X1 X2

Ø

X1 X2

T0

Ladder diagram complied into instruction

LD	T0
LD	X1
AND	X2
ORB

Ladder diagram complied into instruction

LD	X1
AND	X2
OR	T0

In diagram (a), the block on top is shorter than the block in the bottom, we can switch the position of the two blocks to achieve the same logic. Due to that diagram (a) is illegal, there is a “reverse flow” in it.

X0

X1 X2

X3 X4

(a)

Ø

X3 X4

X1 X2

X0

(b)

Ladder diagram complied into instruction

LD	X0
OR	X1
AND	X2
LD	X3
AND	X4

ORB

Ladder diagram complied into instruction

LD	X3
AND	X4
LD	X1
OR	X0
AND	X2
ORB

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1 Basic Principles of PLC Ladder Diagram

MPS and MPP instruction can be omitted when the multiple outputs in the same horizontal line do not need to operate with other input devices.

X0

Y1

Y0

Ø

Y0

X0

Y1

Ladder diagram complied into instruction MPS

AND	X0
OUT	Y1
MPP
OUT	Y0

Ladder diagram complied into instruction

OUT	Y0
AND	X0
OUT	Y1

Correct the circuit of reverse flow

In the following two examples, the diagram in the left hand side is the ladder diagram we desire. However, the illegal “reverse flow” in it is incorrect according to our definition on the ladder diagram. We modify the diagram into the diagram in the right hand side.

Example 1

X0

X1

X2

X0

X1

X2

X3

X4

X5

X3

X4

X5

X10

Ö

X6

X7

X10

LOOP1

X6

X7

X5

reverse flow

X10

LOOP1

Example 2

X0

X1

X2

				X0
X3	X4	X5
				X3
X6	X7	X10	LO OP1	X6
	reverse flow			X3
			Ö
Reverse flow
X0	X1			X6
		X2
X3	X4	X5		X0	X1
X6	X7	X10
			LOOP2

X1		X2
X4		X5
X7		X10
		LOOP1
X4	X7	X10
		LOOP2

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1 Basic Principles of PLC Ladder Diagram

1.7Basic Program Designing Examples

Start, Stop and Latched

In some application occasions, we need to use the transient close/open buttons for the start and stop of an equipment. To maintain its continuous action, you have to design latched circuits.

Example 1: Stop first latched circuit

When the normally open contact X1 = On and the normally closed contact X2 = Off, Y1 will be On. If you make X2 = On at this time, Y1 will be Off. It is the reason why this is called “stop first”.

Y1 X2

Y1

X1

Example 2: Start first latched circuit

When the normally open contact X1 = On and the normally closed contact X2 = Off, Y1 will be On and latched. If you make X2 = On at this time, Y1 will continue to be On because of the latched contact. It is the reason why this is called “start first”.

X1	X2
	Y1
Y1

Example 3: Latched circuit for SET and RST instructions

See the diagram in the right hand side for the latched circuit consist of RST and SET instructions.

In the stop first diagram, RST is placed after SET. PLC executes the program from up to down, so the On/Off of Y1 will be determined upon its status in the end of the program. Therefore, when X1 and X2 are enabled at the same time, Y1 will be Off. It is the reason why this is called “stop first”.

In the start first diagram, SET is placed after RST. When X1 and X2 are enabled at the same time, Y1 will be On. It is the reason why this is called “start first”.

Example 4: Power shutdown latched

The auxiliary relay M512 is latched (see instruction sheets for DVP series PLC MPU). The circuit can not only be latched when the power is on, but also keep the continuity of the original control when the power is shut down and switched on again.

Stop first X1

SET Y1

X2

RST Y1

Start first

X2

RST Y1

X1

SET Y1

X1

SET M512

X2

RST M512

M512

Y1

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1 Basic Principles of PLC Ladder Diagram

Frequently Used Control Circuit

Example 5: Conditional control

X1			X3				Y1		X1
									X3
Y1
									X2

X2

X4

Y1

Y2

X4

Y2

Y1

Y2

X1 and X3 enables and disables Y1; X2 and X4 enables and disables Y2, and all are latched. Due to that the normally open contact of Y1 is connected to the circuit of Y2 in series, Y1 becomes an AND condition for Y2. Therefore, only when Y1 is enabled can Y2 be enabled.

Example 6: Interlock control

X1

X3

Y2

X1

Y1

Y1

X3

X2

X2

X4

X4

Y1

Y2

Y1

Y2

Y2

Which of the X1 and X2 is first enabled decides either the corresponding output Y1 or Y2 will be enabled first. Either Y1 or Y2 will be enabled at a time, i.e. Y1 and Y2 will not be enabled at the same time (the interlock). Even X1 and X2 are enabled at the same time, Y1 and Y2 will not be enabled at the same time due to that the ladder diagram program is scanned from up to down. In this ladder diagram, Y1 will be enabled first.

Example 7: Sequential control

	X1			X3			Y2
											Y1
	Y1
	X2			X4			Y1
											Y2
	Y2

If we serially connect the normally closed contact of Y2 in example 5 to the circuit of Y1 as an AND condition for Y1 (as the diagram in the left hand side), the circuit can not only make Y1 as the condition for Y2, but also allow the stop of Y1 after Y2 is enabled. Therefore, we can make Y1 and Y2 execute exactly the sequential control.

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1 Basic Principles of PLC Ladder Diagram

Example 8: Oscillating circuit

An oscillating circuit with cycle T+ T

Y1			Y1
			Y1

T T

The ladder diagram above is a very simple one. When the program starts to scan the normally closed contact Y1, Y1 will be closed because coil Y1 is Off. When the program then scan to coil Y1 and make it On, the output will be 1. When the program scans to the normally closed contact Y1 again in the next scan cycle, because coil Y1 is On, Y1 will be open and make coil Y1 Off and output 0. The repeated scans will result in coil Y1 outputs oscillating pulses by

the cycle

T(On)+ T(Off).

An oscillating circuit with cycle nT+

T

X0

Y1

X0

TMR T0

Kn

T0

Y1

Y1

nT

T

The ladder diagram program controls the On time of coil Y1 by timer T0 and disable timer T0 in the next scan cycle, resulting in the oscillating pulses in the output of Y1. n refers to the decimal set value in the timer and T is the cycle of the clock.

Example 9: Flashing circuit

X0

T2

X0

TMR

T1

Kn1

T1

TMR

T2

Kn2

n2*T

Y1

X0

T1

Y1

n1*T

The ladder diagram is an oscillating circuit which makes the indicator flash or enables the buzzer alarms. It uses two timer to control the On/Off time of coil Y1. n1 and n2 refer to the set values in T1 and T2 and T is the cycle of the clock.

Example 10: Trigger circuit

X0

M0

X0

M0

Y1

T

Y1

M0

M0

Y1

Y1

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1 Basic Principles of PLC Ladder Diagram

The rising-edge differential instruction of X0 makes coil M0 generate a single pulse of T (one scan cycle).

Coil Y1 will be On during this scan period. In the next scan period, coil M0 will be Off and the normally closed contact M0 and Y1 will all be closed, making coil Y1 continue to be On until another rising-edge arrives in input X0, making coil M0 On for another scan period and Y1 Off. Such kind of circuit relies on an input to make two actions execute interchangeably. Also from the timing diagram on the last page, we can see that input X0 are square pulse signals of the cycle T and coil Y1 output are square pulse signals of the cycle 2T.

Example 11: Delay circuit

X0

X0

TMR

T10 K1000

T10

Y1

Y1

Time base: T = 0.1 sec

100 seconds

When input X0 is On, due to that its corresponding normally closed contact is Off, time T10 will be Off and the output coil Y1 will be On. T10 will be On and start to count until input X0 is Off. Output coil Y1 will be delayed for 100 seconds (K1,000 × 0.1 sec = 100 secs) and be Off. See the timing diagram above.

Example 12: Output delay circuit

The output delay circuit is the circuit composed of two timers. When input X0 is On and Off, output Y4 will be delayed.

X0

TMR T5 K50

T5 T6

Y4 Y4

Y4 X0

TMR T6 K30

5 secs

T5

T

T6

3 secs

Example13: Timing extension circuit

X0						The total delay time from input X0 is closed to output
				TMR	T11	Kn1
T11						Y1 is On = (n1+n2)* T. T refers to the clock cycle.
				TMR	T12	Kn2

T12	Y1	X0
		n1* T
		T11
Timer = T11, T12		n2* T
Clock cycle: T		T12
		Y1
		(n1+n2)* T

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1 Basic Principles of PLC Ladder Diagram

Example 14: How to enlarge the counting range

X13

CNT C5 Kn1

C5

CNT C6 Kn2

RST C5

X14

RST C6

C6

Y1

The counting range of a 16-bit counter is 0 ~ 32,767. As the circuit in the left hand side, using two counters can increase the counting range to n1*n2. When the counting of counter C5 reaches n1, C6 will start to count for one time and reset for counting the pulses from X13. When the counting of counter C6 reaches n2, the pulses from input X13 will be n1*n2.

Example 15: Traffic light control (by using step ladder instruction)

Traffic light control

Vertical

Red light

Yellow

Green

Green

light

light

light

Light

flashes

Vertical

Y0

Y1

Y2

Y2

light

Horizontal

Y10

Y11

Y12

Y12

Horizontal

light

Light

On time

35 secs

5 secs

25 secs

5 secs

Timing Diagram:

Vertical

Light

Red Y0

Yellow Y1

Green Y2

25 secs

Horizontal

5 secs 5 secs

Light

Red Y10

Yellow Y11

Green Y12

25 secs

5 secs

5 secs

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1 Basic Principles of PLC Ladder Diagram

SFC Figure:

M1002

S0

S20

Y0

S30

T0

TMR

T0

K350

T10

Y2

S21

S31

T1

TMR

T1

K250

T11

S22

TMR

T2

K50

S32

M1013

Y2

T2

T12

S23

Y1

S33

T13

S0

			Ladder Diagram:
			M1002		ZRST	S0	S127
					SET	S0
Y12			S0		SET	S20
TMR	T10	K250	S
					SET	S30
TMR	T11	K50
			S20
M1013					Y0
	Y12		S
Y11					TMR	T0	K350
TMR	T12	K50		T0	SET	S21
	Y10		S21
			S		Y2
TMR	T13	K350			TMR	T1	K250
				T1	SET	S22
			S22		TMR	T2	K50
			S
				M1013
					Y2
				T2	SET	S23
			S23
			S		Y1
			S30		Y12
			S
					TMR	T10	K250
				T10	SET	S31
			S31		TMR	T11	K50
			S
				M1013
					Y12
				T11	SET	S32
			S32		Y11
			S
					TMR	T12	K50
				T12	SET	S33
			S33
			S		Y10
					TMR	T13	K350
			S23	S33	T13
			S	S	S0
					RET
					END

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1 Basic Principles of PLC Ladder Diagram

Drawing by SFC Editor (WPLSoft )

Drawn by SFC		Internal Ladder Diagram
		LAD-0
		M1002
		ZRST	S0	S127
LAD-0		SET	S0
S0
		Transferring Condition 1
0
		T0
		TRANS*
S20	S30
1	5	S22
S21	S31
2	6	TMR	T2	K50
		M1013
S22	S32
		Y2
3	7
S23	S33	Transferring Condition 4
		T13
		TRANS*
4
S0		Transferring Condition 7
		T12
		TRANS*

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1 Basic Principles of PLC Ladder Diagram

MEMO

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2 Functions of Devices in DVP-PLC

2.1All Devices in DVP-PLC

ES/EX/SS series MPU:

	Type	Device			Item		Range			Function
		X	External input relay				X0 ~ X177, 128 points, octal		Total	Corresponds to external
										input points
		Y	External output relay				Y0 ~ Y177, 128 points, octal		256 points	Corresponds to external
										output points
				General purpose			M0 ~ M511, M768 ~ M999, 744
							points
			Auxiliary						Total	The contact can be
		M		Latched*			M512 ~ M767, 256 points
			relay						1,280 points	On/Off in the program.
				Special purpose			M1000 ~ M1279, 280 points
							(some are latched)
				100ms timer			T0 ~ T63, 64 points			Timer indicated by TMR
							T64 ~ T126, 63 points (M1028		Total	instruction. If timing
	(bit)	T	Timer	10ms timer (M1028 = On)						reaches its target, the T
							= Off: 100ms)		128 points
										contact of the same No.
	Relay									will be On.
				1ms timer			T127, 1 points
				16-bit counting up			C0 ~ C111, 112 points		Total
				(general purpose)
									128 points	Counter indicated by
				16-bit counting up (latched*)			C112 ~ C127, 16 points
				32-bit		1-phase 1 input	C235 ~ C238, C241, C242,			CNT (DCNT) instruction.
		C	Counter	counting			C244, 7 points			If counting reaches its
				up/down					Total	target, the C contact of
						1-phase 2 inputs	C246, C247, C249, 3 points
				high-speed					13 points	the same No. will be On.
				counter		2-phase 2 inputs	C251, C252, C254, 3 points
				(latched*)
				Initial step (latched*)			S0 ~ S9, 10 points		Total
		S	Step	Zero return (latched*)			S10 ~ S19, 10 points (used with			Used for SFC.
							IST instruction)		128 points
				Latched*			S20 ~ S127, 108 points
										When the timing
		T	Present value of timer				T0 ~ T127, 128 points			reaches the target, the
	data)									contact of the timer will
										be On.
	(word						C0 ~ C127, 16-bit counter, 128 points			When the counting
		C	Present value of counter							reaches the target, the
							C235 ~ C254, 32-bit counter, 13 points			contact of the counter
	Register									will be On.
			Data		General purpose		D0 ~ D407, 408 points		600 points	storage; E, F can be
									Total	Memory area for data
		D	register		Latched*		D408 ~ D599, 192 points			used for index
					Special purpose		D1000 ~ D1311, 312 points		Total
										indication.
					Index indication		E, F, 2 points		312 points
		N	For master control nested loop				N0 ~ N7, 8 points			Control point for main
										control loop
		P	For CJ, CALL instructions				P0 ~ P63, 64 points			Position index for CJ
	Pointer									and CALL
					External interruption		I001, I101, I201, I301, 4 points
										Position index for
		I	Interruption		Timed interruption		I6□□, 1 point (□□ 10 ~ 99,		time base =
							1ms ) (for V5.7 and above)			interruption subroutine.
					Communication interruption		I150, 1 point
	Constant	K	Decimal form				K-32,768 ~ K32,767 (16-bit operation)
							H0000 ~ HFFFF (16-bit operation)
		H	Hexadecimal form
							K-2,147,483,648 ~ K2,147,483,647 (32-bit operation)
							H00000000 ~ HFFFFFFFF (32-bit operation)

* The latched area is fixed and cannot be changed.

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2 Functions of Devices in DVP-PLC

SA/SX/SC series MPU:

Type	Device			Item	Range			Function
	X	External input relay			X0 ~ X177, 128 points, octal		Total	Corresponds to external
								input points
							256
								Corresponds to external
	Y	External output relay			Y0 ~ Y177, 128 points, octal		points
								output points
				General purpose	M0 ~ M511, 512 points (*1)		Total
	M	Auxiliary		Latched*	M512 ~ M999, 488 points (*3)			The contact can be
							4,096
		Relay			M2000 ~ M4095, 2,096 points (*3)			On/Off in the program.
				Special purpose	M1000 ~ M1999, 1,000 points		points
					(some are latched)
					T0 ~ T199, 200 points (*1)
				100ms	T192 ~ T199 for subroutine
					T250 ~ T255, 6 accumulative points			Timer indicated by TMR
					(*4)
							Total	instruction. If timing
	T	Timer			T200 ~ T239, 40 points (*1)		256	reaches its target, the T
				10ms	T240 ~ T245, 6 accumulative points		points	contact of the same No.
					(*4)			will be On.
				1ms	T246 ~ T249, 4 accumulative points
					(*4)
(bit)
				16-bit counting up	C0 ~ C95, 96 points (*1)		Total
Relay					C96 ~ C199, 104 points (*3)		235
				32-bit counting up/down	C216 ~ C234, 19 points (*3)
							points
					C200 ~ C215, 16 points (*1)
					C235 ~ C244, 1-phase 1 input, 9
					points (*3)		Total	Counter indicated by
				For SA/SX, 32-bit	C246 ~ C249, 1-phase 2 inputs, 3
							16	CNT (DCNT) instruction.
	C	Counter		high-speed counter	points (*3)
							points	If counting reaches its
					C251 ~ C254, 2-phase 2 inputs, 4
								target, the C contact of
					points (*3)
								the same No. will be On.
					C235 ~ C245, 1-phase 1 input, 11
					points (*3)		Total
				For SC, 32-bit high-speed	C246 ~ C250, 1-phase 2 inputs, 4
							19
				counter	points (*3)
							points
					C251 ~ C255, 2-phase 2 inputs, 4
					points (*3)
				Initial step	S0 ~ S9, 10 points (*1)
				Zero return	S10 ~ S19, 10 points (used with IST		Total
					instruction) (*1)
	S	Step point					1,024	Used for SFC.
				General purpose	S20 ~ S511, 492 points (*1)
							points
				Latched*	S512 ~ S895, 384 points (*3)
				Alarm	S896 ~ S1023, 128 points (*3)
								When the timing
	T	Present value of timer			T0 ~ T255, 256 points			reaches the target, the
								contact of the timer will
data)								be On.
	C	Present value of counter			C0 ~ C199, 16-bit counter, 200 points			When the counting
(word					C200 ~ C254, 32-bit counter, 50 points (SC: 53			reaches the target, the
					points)			will be On.
								contact of the counter
Register				General purpose	D0 ~ D199, 200 points (*1)		Total	Memory area for data
					D200 ~ D999, 800 points (*3)
	D	Data		Latched*				storage; E, F can be
							5,000
		register			D2000 ~ D4999, 3,000 points (*3)			used for index
				Special purpose	D1000 ~ D1999, 1,000 points		points	indication.
				Index indication	E0 ~ E3, F0 ~ F3, 8 points (*1)
	N/A	File register			K0 ~ K1,599 (1,600 points) (*4)			Expanded register for
								data storage.

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