Basics of PLCs

5/20/2018 Basics of PLCs

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Table of Contents

Introduction ..............................................................................2

PLCs .........................................................................................4

Number Systems ......................................................................8

Terminology ............................................................................14

Basic Requirements ................................................................22

S7-200 Micro PLCs .................................................................26

Connecting External Devices ..................................................37

Programming a PLC ................................................................39

Discrete Inputs/Outputs .........................................................47

Analog Inputs and Outputs .....................................................57

Timers .....................................................................................60

Counters .................................................................................67

High-Speed Instructions .........................................................7

Specialized Expansion Modules ............................................. 74

Review Answers .....................................................................80

Final Exam ..............................................................................81

quickSTEP Online Courses .....................................................84


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2

Introduction

Welcome to another course in the STEP series, SiemensTechnical Education Program, designed to prepare ourdistributors to sell Siemens Energy & Automation productsmore effectively. This course covers Basics of PLCsand related

products.

Upon completion of Basics of PLCsyou should be able to:

Identify the major components of a PLC and describetheir functions

Convert numbers from decimal to binary, BCD, andhexadecimal

Identify typical discrete and analog inputs and outputs

Read a basic ladder logic diagram and statement list

Identify operational differences between different S7-200models

Identify the proper manual to refer to for programming orinstallation of an S7-200 PLC

Connect a simple discrete input and output to an S7-200

Select the proper expansion module for analog inputs andoutputs

Describe the operation of timers and counters


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This knowledge will help you better understand customerapplications. In addition, you will be better able to describeproducts to customers and determine important differencesbetween products. You should complete Basics of Electricity

before attempting Basics of PLCs. An understanding of manyof the concepts covered in Basics of Electricityis required

for Basics of PLCs. In addition, you may wish to complete

Basics of Control Components. Devices covered in Basicsof Control Componentsare used with programmable logiccontrollers.

If you are an employee of a Siemens Energy & Automationauthorized distributor, fill out the final exam tear-out card andmail in the card. We will mail you a certificate of completion if

you score a passing grade. Good luck with your efforts.

SIMATIC, STEP 7, STEP 7-Micro, STEP 7-Micro/WIN, PG 702,and PG 740 are registered trademarks of Siemens Energy &

Automation, Inc.

Other trademarks are the property of their respective owners.


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4

PLCs

A Programmable Logic Controller (PLC), also referred toas programmable controller, is the name given to a type ofcomputer commonly used in commercial and industrial control

applications. PLCs differ from office computers in the types oftasks that they perform and the hardware and software theyrequire to perform these tasks. While the specific applicationsvary widely, all PLCs monitor inputs and other variable values,make decisions based on a stored program, and controloutputs to automate a process or machine. This course ismeant to supply you with basic information on the functions

and configurations of PLCs with emphasis on the S7-200PLCfamily.

Photo Sensors

Lights Pumps

PushbuttonSwitches

Drive Motors

Basic PLC Operation The basic elements of a PLC include input modulesorpoints,

a Central Processing Unit (CPU), output modulesor points,

and a programming device. The type of input modules orpoints used by a PLC depend upon the types of input devicesused. Some input modules or points respond to digital inputs,also called discrete inputs, which are either on or off. Othermodules or inputs respond to analog signals. These analogsignals represent machine or process conditions as a range ofvoltage or current values. The primary function of a PLCs input

circuitry is to convert the signals provided by these variousswitches and sensors into logic signals that can be used by theCPU.


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The CPU evaluates the status of inputs, outputs, and othervariables as it executes a stored program. The CPU then sendssignals to update the status of outputs.

Output modules convert control signals from the CPU intodigital or analog values that can be used to control various

output devices.

The programming device is used to enter or change the PLCsprogram or to monitor or change stored values. Once entered,the program and associated variables are stored in the CPU.

In addition to these basic elements, a PLC system may alsoincorporate an operator interface device of some sort to

simplify monitoring of the machine or process.

In the simple example shown below, pushbuttons (sensors)connected to PLC inputs, are used to start and stop a motor

connected to a PLC output through a motor starter (actuator).No programming device or operator interface are shown in thissimple example.

PLC

Start/Stop Pushbuttons(Sensors)

Motor Starter(Actuator)

Motor

Input

Output


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6

Hard-Wired Control Prior to PLCs, many control tasks were performed bycontactors, control relays and other electromechanical devices.This is often referred to as hard-wired control. Circuitdiagrams had to be designed, electrical components specifiedand installed, and wiring lists created. Electricians would then

wire the components necessary to perform a specific task. Ifan error was made, the wires had to be reconnected correctly.

A change in function or system expansion required extensivecomponent changes and rewiring.

OL

M

CR

CR

L1T1

T2

T3

L2

L3

OL

OL

OL

M

M

CR

MMotor

StartStop

460 VAC

24 VAC

1

2

Advantages of PLCs PLCs not only are capable of performing the same tasks ashard-wired control, but are also capable of many more complexapplications. In addition, the PLC program and electroniccommunication lines replace much of the interconnecting wiresrequired by hard-wired control. Therefore, hard-wiring, thoughstill required to connect field devices, is less intensive. This alsomakes correcting errors and modifying the application easier.

Some of the additional advantages of PLCs are as follows:

Smaller physical size than hard-wire solutions. Easier and faster to make changes.

PLCs have integrated diagnostics and override functions.

Diagnostics are centrally available.

Applications can be immediately documented.

Applications can be duplicated faster and less expensively.

Siemens PLCs Siemens makes several PLC product lines in the SIMATIC S7family. They are: S7-200, S7-300, and S7-400.


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S7-200 The S7-200 is referred to as a micro PLC because of its smallsize. The S7-200 has a brick design, which means that theCPU, power supply, and some inputs/outputs (I/O) are includedin a compact brick-like structure.

While the S7-200 is cost-effective for use on smaller, stand-

alone applications. It can also be connected to other PLCs and

intelligent devices for more complex applications.

S7-300 and S7-400 The S7-300 and S7-400 PLCs are generally used in applicationthat require a greater number of I/O points than an S7-200 can

provide or that require the more advanced features. S7-300and S7-400 PLCs use a modular design with a wide rangeof modules available. Choosing either the S7-300 or S7-400depends on the complexity of the task and possible futureexpansion. Your Siemens sales representative can provide youwith additional information on any of the Siemens PLCs.


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8

Number Systems

Since a PLC is a computer, it stores information in the form ofon or off conditions (1 or 0), referred to as bits. Sometimes bitsare used individually and sometimes they are used to represent

numerical values. Understanding how these bits can be usedto represent numerical values requires an understanding of thebinary number system.

Decimal System In order to understand the binary number system, it isfirst useful to recall some of the basics of the decimalnumber system. All number systems have the same three

characteristics: digits, base, weight. For example, the decimalsystem has the following characteristics:

Ten digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9Base 10Weights 1, 10, 100, 1000, ...

Binary System The binary systemis used by programmable controllers. Thebinary system has the following characteristics:

Two digits: 0, 1

Base 2Weights Powers of base 2 (1, 2, 4, 8, 16, ...)

In the binary system 1s and 0s are arranged into columns. Eachcolumn is weighted. The first column on the right has a binaryweight of 2

0. This is equivalent to a decimal 1 and is referred to

as the least significant bit. The binary weight is doubled with

each succeeding column. The next column, for example, has aweight of 2

1, which is equivalent to a decimal 2. The number in

the far left hand column is referred to as the most significant

bit. In this example, the most significant bit has a binary weightof 27. This is equivalent to a decimal 128.


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Converting Binary The following steps can be used to interpret a decimalto Decimal number from a binary value.

1) Search from least to most significant bit for 1s.2) Write down the decimal representation of each colum

containing a 1.

3) Add the column values.

In the following example, the fourth and fifth columns from theright contain a 1. The decimal value of the fourth column fromthe right is 8, and the decimal value of the fifth column fromthe right is 16. The decimal equivalent of this binary number is24. The sum of all the weighted columns that contain a 1 is thedecimal number that the PLC has stored.

In the following example the fourth and sixth columns from theright contain a 1. The decimal value of the fourth column fromthe right is 8, and the decimal value of the sixth column fromthe right is 32. The decimal equivalent of this binary number is40.

Bits, Bytes, and Words Each binary piece of data is abit. Eight bits make up one byte

Two bytes, or 16 bits, make up one word.


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10

Logic 0, Logic 1 While PLCs are capable of sensing and generating analogvalues, internally, programmable controllers use signals that areon or off. These on and off conditions correspond to the binaryvalues 1 and 0. For example, a binary 0, also called logic 0, canbe used to indicate that a switch is off and a binary 1 (logic 1)

can be used to indicate that a switch is on.

BCD While it is necessary for PLCs to use binary values, humansoften need to see values represented in decimal. As a result,some input and output devices provide a decimal display whereeach decimal digit corresponds to four PLC binary inputs oroutputs. The most common system used by input and outputdevices of this type is referred to as Binary-Coded Decimal(BCD).

One example of a BCD device is a type of four-digitthumbwheel switch. Each thumbwheel digit controls fourPLC inputs. This means that for a four-digit thumbwheel, 16inputs are required. Because each thumbwheel digit onlyneeds to represent decimal values from 0 through 9, only tencorresponding binary values are required for each digit.


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Hexadecimal Hexadecimalis another system used in PLCs. The hexadecimsystem has the following characteristics:

16 digits 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, A, B, C, D, E, FBase 16Weights Powers of base 16 (1, 16, 256, 4096 ...)

The ten digits of the decimal system are used for the first tendigits of the hexadecimal system. The first six letters of thealphabet are used for the remaining six digits.

A = 10 D = 13B = 11 E = 14C = 12 F = 15

The hexadecimal system is used in PLCs because it allows thestatus of a large number of binary bits to be represented in asmall space such as on a computer screen or programming

device display. Each hexadecimal digit represents the exactstatus of four binary bits. To convert a decimal number to ahexadecimal number the decimal number is divided by the basof 16. To convert decimal 28, for example, to hexadecimal:

Decimal 28 divided by 16 is 1 with a remainder of 12. Twelve isequivalent to C in hexadecimal. The hexadecimal equivalent ofdecimal 28 is 1C.

The decimal value of a hexadecimal number is obtained bymultiplying the individual hexadecimal digits by the base 16weight and then adding the results. In the following examplethe hexadecimal number 2B is converted to its decimalequivalent of 43.

160 = 1

161

= 16B = 11


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Conversion of Numbers The following chart shows a few numeric values in decimal,binary, BCD, and hexadecimal representation.


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Review 11. Identify each of the following blocks which are part of a

basic PLC system:

2. The base of the binary number system is ___ .

3. The base of the hexadecimal number system is ___.

4. Convert a decimal 10 to the following:

Binary ____________

BCD ____________

Hexadecimal ____________


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14

Terminology

Developing an understanding of PLCs requires learning somebasic terminology commonly used to describe these devicesand related components.

Sensors Sensorsare devices that convert a physical condition into anelectrical signal for use by the PLC. Sensors are connected tothe input of a PLC. A pushbutton is one example of a sensorthat is connected to the PLC input. An electrical signal is sentfrom the pushbutton to the PLC indicating the condition (open/closed) of the pushbutton contacts.

Actuators Actuatorsare devices that convert an electrical signal from thePLC into a physical condition. Actuators are connected to thePLC output. A motor starter is one example of an actuator thatis connected to the PLC output. Depending on the output PLC

signal the motor starter will either start or stop the motor.


PLCOutput 1 Motor


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Discrete Input A discrete input, also referred to as a digital input, is aninput that is either on or off. Pushbuttons, toggle switches,limit switches, proximity switches, and contact closures areexamples of discrete sensors which are connected to thePLCs discrete or digital inputs. In the ON condition a discreteinput may be referred to as a logic 1 or a logic high. In the OFF

condition a discrete input may be referred to as a logic 0 or a

logic low.

A normally open (NO) pushbutton is used in the followingexample. Many PLCs require a separate power supply to poweits inputs; however, this example is for a PLC that powers itsown inputs. One side of the pushbutton is connected to the

first PLC input. The other side of the pushbutton is connectedto an internal 24 VDC power supply. With the pushbutton in theopen state, no voltage is present at the PLC input. This is theOFF condition. When the pushbutton is depressed, 24 VDC isapplied to the PLC input. This is the ON condition.


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Analog Inputs An analog inputis a continuous, variable signal. Typical analoginputs may vary from 0 to 20 milliamps, 4 to 20 milliamps,or 0 to 10 volts. In the following example, a level transmittermonitors the level of liquid in a tank. Depending on the leveltransmitter, the signal to the PLC can either increase or

decrease as the level in the tank increases.

Discrete Outputs A discrete outputis an output that is either on or off.Solenoids, contactor coils, and lamps are examples of actuatordevices connected to discrete outputs. Discrete outputs mayalso be referred to as digital outputs. In the following example, alamp can be turned on or off by the PLC output it is connectedto.

Analog Outputs An analog outputis a continuous, variable signal. The outputmay be as simple as a 0-10 VDC level that drives an analogmeter. Examples of analog meter outputs are speed, weight,and temperature. The output signal may also be used on morecomplex applications such as a current-to-pneumatic transducer

that controls an air-operated flow-control valve.


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CPU The central processor unit (CPU)is a microprocessor systemthat contains the system memory and is the PLC decision-making unit. The CPU monitors the inputs, outputs, and othervariables and makes decisions based on instructions held inthe program memory. Typical CPU operations include relay,counting, timing functions, data comparison, sequencing, and

arithmetic operations.

Programming A program consists of instructions that accomplish one ormore tasks. The degree of complexity of the PLCs program

depends upon the complexity of the task to be performed, thenumber and type of input and output devices, and the types ofinstructions used. Some PLC programs are made up primarilyof ladder logic instructions, but other approaches such as

statement lists or function block diagrams are also common.

Ladder Logic Ladder logic(LAD) is one programming language used withPLCs. Ladder logic uses components that resemble elementsused in a line diagram format to describe hard-wired control.Refer to the STEP course Basics of Control Componentsformore information on line diagrams.


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Ladder Logic Diagram The left vertical line of a ladder logic diagramrepresents thepower or energized conductor. The output element or instructionrepresents the neutral or return path of the circuit. The rightvertical line, which represents the return path on a hard-wiredcontrol line diagram, is omitted. Ladder logic diagrams are readfrom left-to-right, top-to-bottom. Rungs are sometimes referred

to as networks. A network may have several control elements,

but only one output coil.

In the example program shown example I0.0, I0.1 and Q0.0represent the first instruction combination. If inputs I0.0 andI0.1 are energized, output relay Q0.0 energizes. The inputs could

be switches, pushbuttons, or contact closures. I0.4, I0.5, and

Q1.1 represent the second instruction combination. If eitherinput I0.4 or I0.5 are energized, output relay Q0.1 energizes.

Statement list A statement list (STL)provides another view of a set ofinstructions. The operation, what is to be done, is shown on theleft. The operand, the item to be operated on by the operation,is shown on the right. A comparison between the statement

list shown below, and the ladder logic shown on the previouspage, reveals a similar structure. The set of instructions in thisstatement list perform the same task as the ladder diagram.


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Function Block Diagrams Function Block Diagrams (FBD)provide another view of aset of instructions. Each function has a name to designate itsspecific task. Functions are indicated by a rectangle. Inputsare shown on the left-hand side of the rectangle and outputsare shown on the right-hand side. The function block diagramshown below performs the same function as shown by the

ladder diagram and statement list.

PLC Scan The PLC program is executed as part of a repetitive process

referred to as a scan. A PLC scan starts with the CPU readingthe status of inputs. The application program is executed using

the status of the inputs. Once the program is completed, theCPU performs internal diagnostics and communication tasks.The scan cycle ends by updating the outputs, then starts over.The cycle time depends on the size of the program, the numbeof I/Os, and the amount of communication required.

Software Softwareis the name given to computer instructionsregardless of the programming language. Essentially, softwareincludes the instructions or programs that direct hardware.

Hardware Hardwareis the name given to all the physical componentsof a system. The PLC, the programming device, and theconnecting cable are examples of hardware.


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Memory Size Kilo, abbreviated K, normally refers to 1000 units. When talkingabout computer or PLC memory, however, 1K means 1024. Thisis because of the binary number system (2

10=1024). This can be

1024 bits, 1024 bytes, or 1024 words, depending on memorytype.

RAM Random Access Memory (RAM)is memory where data canbe directly accessed at any address. Data can be written toand read from RAM. RAM is used as a temporary storage area.RAM is volatile, meaning that the data stored in RAM will belost if power is lost. A battery backup is required to avoid losingdata in the event of a power loss.

ROM Read Only Memory (ROM)is a type of memory that data canbe read from but not written to. This type of memory is usedto protect data or programs from accidental erasure. ROMmemory is nonvolatile. This means a user program will not losedata during a loss of electrical power. ROM is normally used tostore the programs that define the capabilities of the PLC.

EPROM Erasable Programmable Read Only Memory (EPROM)provides some level of security against unauthorized orunwanted changes in a program. EPROMs are designed sothat data stored in them can be read, but not easily altered.Changing EPROM data requires a special effort. UVEPROMs(ultraviolet erasable programmable read only memory) can onlybe erased with an ultraviolet light. EEPROM (electronicallyerasable programmable read only memory), can only be erasedelectronically.

Firmware Firmwareis user or application specific software burned into

EPROM and delivered as part of the hardware. Firmware givesthe PLC its basic functionality.


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Putting it Together The memory of the S7-200 is divided into three areas:programspace, data space, and configurable parameter space.

Program space stores the ladder logic (LAD) or statementlist (STL) program instructions. This area of memory controthe way data space and I/O points are used. LAD or STLinstructions are written using a programming device such a

a PC, then loaded into program memory of the PLC.

Data space is used as a working area, and includes memolocations for calculations, temporary storage of intermediat

results and constants. Data space includes memorylocations for devices such as timers, counters, high-speedcounters, and analog inputs and outputs. Data space can baccessed under program control.

Configurable parameter space, or memory, stores either th

default or modified configuration parameters.


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Basic Requirements

The following items are needed to create or change a PLCprogram: PLC, programming device, programming software,and connector cable

PLC Throughout this course we will be using the S7-200 for specificexamples of PLC concepts. The S7-200 is used for this purposebecause of its ease of use and wide-spread application.

Programming Devices The program is created in a programming device (PG)and

then transferred to the PLC. The program for the S7-200can be created using a dedicated Siemens SIMATIC S7programming device, such as a PG 720 (not shown) or PG 740,if STEP 7 Micro/WINsoftware is installed.


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A personal computer (PC), with STEP 7 Micro/WIN installed,can also be used as a programming device with the S7-200.

Software A software program is required in order to tell the PLC what

instructions it must follow. Programming software is typicallyPLC specific. A software package for one PLC, or one familyof PLCs, such as the S7 family, would not be useful on otherPLCs. The S7-200 uses a Windows based software programcalled STEP 7-Micro/WIN32. The PG 720 and PG 740 have STE7 software pre-installed. Micro/WIN32 is installed on a personacomputer in a similar manner to any other computer software.


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Connector Cables PPI Connector cablesare required to transfer data from the(Point-to-Point Interface) programming device to the PLC. Communication can only

take place when the two devices speak the same language orprotocol. Communication between a Siemens programmingdevice and the S7-200 is referred to as PPI protocol (point-to point interface). An appropriate cable is required for a

programming device such as a PG 720 or PG 740. The S7-200

uses a 9-pin, D-connector. This is a straight-through serial devicethat is compatible with Siemens programming devices (MPIport) and is a standard connector for other serial interfaces.

Programming Device Cable

SF/DIAG

A special cable is needed when a personal computer is used asa programming device. Two versions of this cable are available.

One version, called an RS-232/PPI Multi-Master Cable,connects a personal computers RS-232 interface to the PLCsRS-485 connector. The other version, called a USB/PPI Multi-

Master Cable, connects a personal computers USB interfaceto the PLCs RS-485 connector.


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Review 21. A switch or a pushbutton is a ____________ input.

2. A lamp or a solenoid is an example of a ___________output.

3. The _____ makes decisions and executes control

instructions based on the input signals.

4. ____________ ____________ is a PLC programminglanguage that uses components resembling elementsused in a control line diagram.

5. A ____________ consists of one or more instructionsthat accomplish a task.

6. S7-200 PLC memory is divided into the following threespaces: _________, ______, and __________ ________.

7. When talking about computer or PLC memory, 1Krefers to ______ bits, bytes, or words.

8. Software that is burned into EPROM is called____________ .

9. Which of the following is not required when creating orchanging a PLC program?

a. PLC b. Programming Device

c. Programming Software d. Connector Cable e. Printer

10. An RS-232/PPI Multi-Master cable or a USB/PPI-Multi-Master cable may be used to connect a personalcomputer to the PLCs __________ connector.


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S7-200 Micro PLCs

The S7-200 Micro PLC is the smallest member of the SIMATICS7 family of programmable controllers. The central processingunit (CPU) is internal to the PLC. Inputs and outputs (I/O) are

the system control points. Inputs monitor field devices, such asswitches and sensors. Outputs control other devices, such asmotors and pumps. The programming port is the connection tothe programming device.

S7-200 Models There are five S7-200 CPU types: CPU 221, CPU 222, CPU 224,CPU 224XP, and CPU 226and two power supply configurationsfor each type.

Model Description Power Supply Input Types Output Types

221 DC/DC/DC 20.4-28.8 VDC 6 DC 4 DC

221 AC/DC/Relay 85-264 VAC, 47-63 Hz 6 DC 4 Relay

222 DC/DC/DC 20.4-28.8 VDC 8 DC 6 DC


224 DC/DC/DC 20.4-28.8 VDC 14 DC 10 DC


224XP DC/DC/DC 20.4-28.8 VDC 14 DC, 2 Analog 10 DC, 1 Analog

224XP AC/DC/Relay 85-264 VAC, 47-63 Hz 14 DC, 2 Analog 10 Relay, 1 Analog

226 DC/DC/DC 20.4-28.8 VDC 24 DC 16 DC


The model description indicates the type of CPU, the powersupply, the type of input, and the type of output.


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S7-200 Features The S7-200 family includes a range of CPUs which providea variety of features to aid in designing a cost-effectiveautomation solution. The following table provides a summary othe major features, many of which are covered in this course.

Feature CPU 221 CPU 222 CPU 224 CPU 224XP CPU 226

Program (with run mode edit) 4096 Bytes 4096 Bytes 8192 Bytes 12288 Bytes 16384 Bytes

Program (w/o run mode edit) 4096 Bytes 4096 Bytes 12288 Bytes 16384 Bytes 24576 Bytes

User Data 2048 Bytes 2048 Bytes 8192 Bytes 10240 Bytes 10240 Bytes

Memory Type EEPROM EEPROM EEPROM EEPROM EEPROM

Memory Cartridge EEPROM EEPROM EEPROM EEPROM EEPROM

Data Backup (super cap) 50 Hours 50 Hours 100 Hours 100 Hours 100 Hours

Data Backup (opt. battery) 200 Days 200 Days 200 Days 200 Days 200 Days

Local Digital I/O 6 In/4 Out 8 In/6 Out 14 In/10 Out 14 In/10 Out 24 In/16 Out

Local Analog I/O None None None 2 In/1 Out NoneMax Expansion Modules None 2 7 7 7

Boolean Execution Speed 0.22 s/Inst. 0.22 s/Inst. 0.22 s/Inst. 0.22 s/Inst. 0.22 s/Inst.

Internal Relays 256 256 256 256 256

Counters 256 256 256 256 256

TImers 256 256 256 256 256

Sequential Control Relays 256 256 256 256 256

For/Next Loops Yes Yes Yes Yes Yes

Integer Math (+-*/) Yes Yes Yes Yes Yes

Floating-Point Math (+-*/) Yes Yes Yes Yes Yes

High-Speed Counters 4 (30 KHz) 4 (30 KHz) 6 (30 KHz)

4 (30 KHz),

2 (200 KHz) 6 (30 KHz)

Analog Adjustments 1 1 2 2 2

Pulse Outputs (DC) 2 (20 KHz) 2 (20 KHz) 2 (20 KHz) 2 (100 KHz) 2 (20 KHz)

Timed Interrupts 2 (1 - 255ms) 2 (1 - 255ms) 2 (1 - 255ms) 2 (1 - 255ms) 2 (1 - 255ms)

Edge Interrupts 4 4 4 4 4

Real-Time Clock Optional Optional Built-In Built-In Built-In

Password Protection Yes Yes Yes Yes Yes

Number of Ports 1 (RS-485) 1 (RS-485) 1 (RS-485) 2 (RS-485) 2 (RS-485)

Protocols SupportedPPI, MPI,

Freeport

PPI, MPI,

Freeport

PPI, MPI,

Freeport

PPI, MPI,

Freeport

PPI, MPI,

Freeport

Peer-to-Peer PPI Master Mode (NETR/NETW) (NETR/NETW) (NETR/NETW) (NETR/NETW) (NETR/NETW)

Enhanced Features

Communications

Memory

Instructions

I/O


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Mode Switch and When the mode switchis in the RUN position the CPU is inAnalog Adjustment the run mode and executing the program. When the mode

switch is in the STOP position the CPU is stopped. When themode switch is in the TERM position the programming devicecan select the operating mode.

The analog adjustmentis used to increase or decrease values

stored in special memory. These values can be used to updatethe value of a timer or counter, or can be used to set limits.

Optional Cartridge The S7-200 supports an optional memory cartridgethatprovides a portable EEPROM storage for your program. Thecartridge can be used to copy a program from one S7-200 PLC

to a like S7-200 PLC.

In addition, two other cartridges are available. A real-time clockwith battery is available for use on the CPU 221 and CPU 222.The battery provides up to 200 days of data retention timein the event of a power loss. The CPU 224, CPU 224XP andCPU 226 have a real-time clock built in. Another cartridge isavailable with a battery only.

SF/DIAG


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Expansion Modules The S7-200 PLCs are expandable. Expansion modulescontaiadditional inputs and outputs. These are connected to the baseunit using a ribbon connector.

The ribbon connector is protected by a cover on the base unit.Side-by-side mounting completely encloses and protects theribbon connector.


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Available Expansion The CPU 221 comes with 6 digital inputs and 4 digital outputs.These are not expandable. The CPU 222 comes with 8 digitalinputs and 6 digital outputs and will accept up to 2 expansionmodules. The CPU 224 and CPU 224XP come with 14 digitalinputs and 10 digital outputs and will accept up to 7 expansion

modules. The CPU 226 comes with 24 digital inputs and 16digital outputs and will accept up to 7 expansion modules.

6 Inputs, 4 Outputs

No Expansion Modules (EM)

8 Inputs, 6 Outputs

Up to 2 Expansion Modules

14 Inputs, 10 Outputs



2 Analog In, 1 Analog Out




CPU221

CPU222

CPU224

CPU224XP

EM EM

CPU226

EM EM

EM EM

EM EM

EM

EM EM EM EM EM EM EM

EM EM

EMEM EM EM EM

Status Indicators The CPU status indicatorsreflect the current mode of CPUoperation. When the CPU is in the RUN mode, the green RUNindicator is lit. When the CPU is in the STOP mode, the yellow

STOP indicator is lit. The System Fault/Diagnostic (SF/DIAG)indicator turns red for a system fault and yellow to indicate

certain diagnostic conditions.

The I/O status indicators represent the on or off status ofcorresponding inputs and outputs. For example, when the CPUsenses an input is on, the corresponding green indicator is lit.


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Mounting The S7-200 can be mounted in one of two ways. A DIN clipallows installation on a standard DIN rail. The DIN clip snapsopen to allow installation and snaps closed to secure theunit on the rail. The S7-200 can also be panel mounted usinginstallation holes located behind the access covers.

External Power Supply An S7-200 can be connected to either a 24 VDC or aSources 120/230 VAC power supply depending on the CPU. An S7-200

DC/DC/DC would be connected to a 24 VDC power supply.

24 VDCPower Supply

An S7-200 AC/DC/Relay would be connected to a120 or 230 VAC power supply.

Neutral

Ground Line


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I/O Numbering S7-200 inputs and outputs are labeled at the wiring terminationsand next to the status indicators. These alphanumeric symbolsidentify the I/O address to which a device is connected. Thisaddress is used by the CPU to determine which input is presentand which output needs to be turned on or off. Idesignates

a discrete input and Qdesignates a discrete output. The firstnumber identifies the byte, the second number identifies the

bit. Input I0.0, for example, is byte 0, bit 0.

I0.0 = Byte 0, Bit 0I0.1 = Byte 0, Bit 1I1.0 = Byte 1, Bit 0I1.1 = Byte 1, Bit 1

The following table identifies the input and output designations.

Inputs Inputdevices, such as switches, pushbuttons, and other sensordevices are connected to the terminal strip under the bottomcover of the PLC.

Input DevicesConnected Here

Pushbutton Switch


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Input Simulator A convenient method of testing a program is to wire toggleswitches to the inputs. Input simulatorswith pre-wired togglswitches are available for the S7-200s. Switches are wiredbetween the 24 VDC power supply (L+) and the inputs. Forexample, the switch on the far left is wired between the firstinput (0.0) and L+. When the switch is closed, 24 VDC is applie

to the input. This is referred to as a logic 1. When the switch

is open, 0 VDC is applied to the input. This is referred to as alogic 0.

Outputs Outputdevices, such as relays, are connected to the terminalstrip under the top cover of the PLC. When testing a program,it is not necessary to connect output devices. The LED statusindicators signal if an output is active.

RelayLight

From Input Power SupplyOutput Devices

Wired Here


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Optional Connector An optional fan-out connectorallows for field wiringconnections to remain fixed when removing or replacing aCPU 221 or CPU 222. The appropriate connector slides intoeither the input, output, or expansion module terminals.

Removable Terminal Strip The CPU 224, CPU 224XP, and CPU 226 do not have an optionalfan-out connector. Instead, the terminal stripsare removable.This allows the field wiring connections to remain fixed whenremoving or replacing the PLC.

Super Capacitor A super capacitor, so named because of its ability to maintaina charge for a long period of time, protects data stored in RAMin the event of a power loss. The RAM memory is typicallybacked up on the CPU 221 and CPU 222 for 50 hours, and on

the CPU 224, CPU 224 XP, and CPU 226 for 100 hours.


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Reference Manual The SIMATIC S7-200 Programmable Controller SystemManualprovides complete information on installing andprogramming the S7-200 PLCs. This manual can be downloadeas a PDF file from the Technical Infolink on the Siemens

S7-S00 web site:

http://www.automation.siemens.com/_en/s7-200/index.htm

Preface, Contents

Product Overview 1

Getting Started 2

Installing the S7-200 3

PLC Concepts 4

Programming Concepts,Conventions and Features

5

S7-200 Instruction Set 6

Communicating over a Network 7

Hardware Troubleshooting Guideand Software Debugging Tools

8

Open Loop Motion Control withthe S7-200

9

Creating a Program for theModem Module

10

Using the USS Protocol Library toControl a MicroMaster Drive

11

Using the Modbus ProtocolLibrary

12

Using Recipes 13

Using Data Logs 14

PID Auto-Tune and the PIDTuning Control Panel

15

Appendices

Index

S7-200Programmable Controller

System Manual

SIMATIC

This manual has the order number:6ES7298-8FA24-8BH0


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Review 3

1. The five models of S7-200 are _____ , _____ , _____ ,_____, and _____ .

2. Which of the following is not available on an CPU 221?

a. Mode Switch

b. Expansion Module c. Programming Port d. Status Indicators

3. A CPU 222 can have a maximum of___ expansionmodules and a CPU 224 can have a maximum of ___

expansion modules.

4. A CPU 222 DC/DC/DC has ___ DC inputs and ___ DCoutputs without expansion modules.

5. A CPU 224 DC/DC/DC has ___ DC inputs and ___ DCoutputs without expansion modules.

6. The fourth output of an S7-200 would be labeled

______ .

7. S7-200 can be panel mounted or installed on a ______rail.


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Connecting External Devices

TD 200 The S7-200 programming port can be used to communicatewith a variety of external devices. One such device is theTD 200text display unit. The TD 200 displays messages readfrom the S7-200, allows adjustment of designated program

variables, provides the ability to force, and permits setting ofthe time and date. The TD 200 can be connected to an externapower supply or receive its power from the S7-200.

ProgrammingDevice Cable

PPI Protocol

SF/DIAG

Freeport Mode The programming port has a mode called freeport mode.Freeport mode allows connectivity to various intelligent sensin

devices such as a bar code reader.

Bar-Code Decoder

Bar-Code Reader

Freeport ModeRS-485 to RS-232Interface

Programming Port


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Printer Freeport mode can also be used to connect to a non-SIMATICprinter.

Freeport Mode

Connecting CableSerial to ParallelConverter

Programming Port

Interconnection It is possible to use one programming device to addressmultiple S7-200 devices on the same communication cable. Atotal of 31 units can be interconnected without a repeater.

IBM orIBM Compatible PC

PPI Interconnection

S7-200 S7-200 S7-200


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Programming a PLC

STEP 7-Micro/WIN32 is the program software used with theS7-200 PLC to create the PLC operating program. STEP 7consists of a number of instructions that must be arrangedin a logical order to obtain the desired PLC operation. These

instructions are divided into three groups: standard instructionspecial instructions, and high-speed instructions.

Standard Instructions Standard instructionsconsists of instructions that are foundin most programs. Standard instructions include: timer, counte

math, logical, increment/decrement/invert, move, and blockinstructions.

Special Instructions Special instructionsare used to manipulate data. Specialinstructions include: shift, table, find, conversion, for/next, andreal-time instructions.

High-Speed Instructions High-speed instructionsallow for events and interrupts to

occur independent of the PLC scan time. These include high-speed counters, interrupts, output, and transmit instructions.

It is not the purpose of this text to explain all of the instructionand capabilities. A few of the more common instructionsnecessary for a basic understanding of PLC operation willbe discussed. PLC operation is limited only by the hardwarecapabilities and the ingenuity of the person programming it.Refer to the SIMATIC S7-200 Programmable Controller

System Manualfor detailed information concerning theseinstructions.


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Micro/WIN32 The programming software can be run off-line or on-line. Off-line programming allows the user to edit the ladder diagramand perform a number of maintenance tasks. The PLC doesnot need to be connected to the programming device in thismode. On-line programming requires the PLC to be connected

to the programming device. In this mode, program changes aredownloaded to the PLC. In addition, status of the input/output

elements can be monitored. The CPU can be started, stopped,or reset.

Symbols The language of PLC ladder logic consists of a commonly usedset of symbols that represent instructions. Understanding thebasic symbols is essential to understanding PLC operation.

Contacts One of the most confusing aspects of PLC programming forfirst-time users is the relationship between the device thatcontrols a status bit and the programming function that uses

a status bit. Two of the most common programming functionsare the normally open (NO) contactand the normallyclosed (NC) contact. Symbolically, power flows through thesecontacts when they are closed. The normally open contact (NO)is closed when the input or output status bit controlling thecontact is 1. The normally closed contact (NC) is closed whenthe input or output status bit controlling the contact is 0.


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Coils Coilsrepresent relays that are energized when power flowsto them. When a coil is energized, it causes a correspondingoutput to turn on by changing the state of the status bitcontrolling that output to 1. That same output status bit may beused to control normally open and normally closed contactselsewhere in the program.

Boxes Boxesrepresent various instructions or functions that are

executed when power flows to the box. Typical box functionsare timers, counters, and math operations.

Entering Elements Control elementsare entered in the ladder diagram bypositioning the cursor and selecting the element from a list.In the following example the cursor has been placed in the

position to the right of I0.2. A coil was selected from a pull-down list and inserted in this position.

Network 1

Network 2

I0.0 I0.1

I0.2

Q0.0

Cursor


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AND Operation Each rung or network on a ladder represents a logic operation.The following programming example demonstrates an ANDoperation. Two contact closures and one output coil are placedon network 1. They are assigned addresses I0.0, I0.1, and Q0.0.Note that in the statement list a new logic operation always

begins with a load instruction (LD). In this example I0.0 (input 1)and (A in the statement list) I0.1 (input 2) must be true in order

for output Q0.0 (output 1) to be true. It can also be seen thatI0.0 and I0.1 must be true for Q0.0 to be true by looking at thefunction block diagram representation.

Another way to see how an AND function works is witha Boolean logic diagram. In Boolean logic, an AND gate isrepresented by a number of inputs on the left side. In this casethere are two inputs. The output is represented on the rightside. It can be seen from the table that both inputs must be a

logic 1 in order for the output to be a logic 1.

I0.0

I0.0

I0.1

I0.1

Q0.0

Q0.0

0011

0101

0001

And (A) Function

Input 1

Input 1

Input 2

Input 2

Output 1

Output 1

0011

0101

0001

And (A) Function


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OR Operation In this example an OR operationis used in network 1. It can bseen that if either input I0.2 (input 3) or (O in the statement lisinput I0.3 (input 4), or both are true, then output Q0.1 (output 2will be true.

Another way to see how an OR function works is with aBoolean logic diagram. The symbol differs slightly from an ANDfunction. The OR function is represented by a number of inputson the left side. In this case there are two inputs. The output isrepresented on the right side. It can be seen from the table thaany input can be a logic 1 in order for the output to be a logic 1

Input 3

Input 3

Input 4

Input 4

Output 2

Output 2

0011

0101

0111

Or (O) Function

I0.4

I0.4

I0.5

I0.5

Q0.1

Q0.1

0011

0101

0111

Or (O) Function


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Testing a Program Once a program has been written it needs to be tested anddebugged. One way this can be done is to simulate the fieldinputs with an input simulator, such as the one made for theS7-200. The program is first downloaded from the programmingdevice to the CPU. The selector switch is placed in the RUN

position. The simulator switches are operated and the resultingindication is observed on the output status indicator lamps.

Status Functions After a program has been loaded and is running in the PLC, theactual status of ladder elements can be monitored using STEP 7Micro/WIN32 software. The standard method of showing aladder element is by indicating the circuit condition it produceswhen the device is in the de-energized or non operated state.In the following illustration, input 1 (I0.0) is programmed as anormally open (NO) contact. In this condition, power will not

flow through the contacts to the output (Q0.0).


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When viewing the ladder diagram in the status mode, controlelements that are active are highlighted. In the following,example the toggle switch connected to input 1 has beenclosed. Power flows through the control element associatedwith input 1 (I0.0), output 1 (Q0.0) is active, and the lamp is on

Forcing Forcingis another useful tool in the commissioning ormaintenance of a PLC system. It can be used to temporarilyoverride the input or output status of the application in order

to test and debug the program. The force function can also beused to override discrete output points or to skip portions of aprogram by enabling a jump instruction with a forced memorybit.

In the example shown below, the toggle switch is open. Undernormal circumstances, the toggle switch would have to beclosed to enable input 1 (I0.0) and turn on the output light.

However, input 1 can be forced on even though the input toggswitch is open. With input 1 forced high, the lamp will be on.When a function is forced the control bit identifier is highlighteThe element is also highlighted because it is on.


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The following table shows the appearance of ladder elements inthe off, forced, and on conditions.


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Discrete Inputs/Outputs

The same simple lamp circuit previously discussed, is useful toreview to understand discrete I/O control. In this example, thelamp is off when the switch is open and on when the switch isclosed.

Wiring To accomplish this task, a switch is wired to an input terminal the PLC and an indicator light is wired to an output terminal.

Light

Switch


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The following drawing illustrates the operation of a simpleprogram that allows a toggle switch to control a lamp. Onceprogrammed, the CPU repetitively scans the status of I/Opoints and the stored program. As long as the toggle switch isopen, the lamp remains off. However, when the toggle switch

closes, the internal status of I0.0 changes to a 1. This causes theI0.0 normally open contact in the program to close, activating

the Q0.0 coil and changing the associated output status bit to 1.On the next scan of the PLCs I/O, the lamp turns on.

Motor Starter Example While the lamp application is useful to explain basic PLCoperation, a more practical, and only slightly more complex,application is start-stop control of an AC motor. Before

examining the PLC application, first consider a hard-wiredapproach.

The line diagram shown below illustrates how a normally open

and a normally closed pushbutton might be connected tocontrol a three-phase AC motor. In this example, a motor startercoil (M) is wired in series with a normally open momentary Startpushbutton, a normally closed momentary Stop pushbutton,and normally closed overload relay (OL) contacts.


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Momentarily depressing the Start pushbutton completes thepath of current flow and energizes the motor starter (M).

This closes the associated M and Ma (auxiliary contact locatedin the motor starter) contacts. When the Start button is

released, current continues to flow through the Stop button an

the Ma contact, and the M coil remains energized. The motorwill run until the normally closed Stop button is pressed unlessthe overload relay (OL) contacts open. When the Stop buttonis pressed, the path of current flow is interrupted opening theassociated M and Ma contacts, and the motor stops.


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This motor control application can also be accomplished with aPLC.

PLC


Motor Starter

(Actuator)

Motor

Input

Output

Program Instruction In the following example, a normally open Start pushbutton iswired to the first input (I0.0), a normally closed Stop pushbuttonis wired to the second input (I0.1), and normally closed overloadrelay contacts (part of the motor starter) are connected to thethird input (I0.2). These inputs are used to control normally opencontacts in a line of ladder logic programmed into the PLC.

Initially, I0.1 status bit is a logic 1 because the normally closed(NC) Stop Pushbutton is closed. I0.2 status bit is a logic 1

because the normally closed (NC) overload relay (OL) contactsare closed. I0.0 status bit is a logic 0, however, because thenormally open Start pushbutton has not been pressed.

Normally open output Q0.0 is also programmed on Network1 as a sealing contact. With this simple network, energizing

output coil Q0.0 is required to turn on the motor.


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When the Start pushbutton is pressed, the CPU receives a log1 from input I0.0. This causes the I0.0 contact to close. All threinputs are now a logic 1. The CPU sends a logic 1 to outputQ0.0. The motor starter is energized and the motor starts.

The output status bit for Q0.0 is now a 1. On the next scan,

when normally open contact Q0.0 is solved, the contact willclose and output Q0.0 will stay on even if the Start pushbutton

is released.

When the Stop pushbutton is pressed, input I0.1 turns off,

the I0.1 contact opens, output coil Q0.0 de-energizes, and themotor turns off.


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Expanding the Application The application can be easily expanded to include indicatorlights for run and stop conditions. In this example, a RUNindicator light is connected to output Q0.1 and a STOP indicatorlight is connected to output Q0.2.

PLC



Motor

Input

Output Indicator Lights

The ladder logic for this application includes a normally openoutput contact Q0.0 connected on Network 2 to output Q0.1and a normally closed Q0.0 contact connected on Network 3 tooutput Q0.2. When Q0.0 is off, the normally open Q0.0 contacton Network 2 is open and the RUN indicator off. At the sametime, the normally closed Q0,0 contact is closed and the STOP

indicator is on.


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When the Start button is pressed, the PLC starts the motor.Output Q0.0 is now on. The normally open Q0.0 contact onNetwork 2 is now closed and the RUN indicator on. At the samtime, the normally closed Q0.0 contact on Network 3 is openand the STOP indicator light connected to output Q0.2 is off.

Adding a Limit Switch The application can be further expanded by adding a limitswitch with normally open contacts to input I0.3.



Motor

Input

Output Indicator Lights

Limit Switch

PLC


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A limit switch could be used to stop the motor or prevent themotor from being started. This limit switch might be associatedwith an access door to the motor, or its associated equipment.If the access door is open, the normally open contacts of LS1connected to input I0.3 are open and the motor will not start.

When the access door closes, the normally open contacts onthe limit switch (LS1) close. Input I0.3 is now on, and the motorwill start when the Start pushbutton is pressed.


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Further Expansion The PLC program can be further expanded to accommodatemany commercial and industrial applications. Additional Start/Stop pushbuttons and indicator lights can be added for remoteoperation, or control of a second motor starter and motor.Over-travel limit switches can be added along with proximityswitches for sensing object position. In addition, expansion

modules can be added to further increase the I/O capability. Th

applications are only limited by the number of I/Os and amounof memory available on the PLC.

I/O Expansion Module

Sensors(Digital Inputs)

Pushbuttons(Digital Inputs)

Motor Starters(Digital Outputs)

Indicator Lights(Digital Outputs)


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Review 4

1. Identify the following symbols:

a. ____________

b. ____________

c. ____________

2. Complete the following tables:

3. In the following network, coil Q0.0 will be on whencontact ____ is closed and either contact____ or contact____ or both are closed.


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Analog Inputs and Outputs

Many PLCs also work with analog I/O devices. Analog devicesuse signals that are continuously variable within a specifiedrange such as 0 to 10 VDC or 4 to 20 mA. Analog signals areused to represent changing values such as speed, temperature

weight, and level. In order to process an input of this type, aPLC must convert the analog signal into a digital representatioFor an S7-200 PLC, this means that an expansion modulecapable of converting the analog signal must be used. TheS7-200 analog modules convert standard voltage and currentanalog values into a 12-bit digital representation. The digital

values are transferred to the PLC for use in register or wordlocations.

In addition, analog modules are available for use withthermocouple and RTD type sensors which sense thetemperature at a specific point in a machine or process.

Analog Expansion Module

SF/DIAG


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Application Example In the following example, a scale is connected to a load cell.A load cell is a device that generates an electrical outputproportional to the force applied. In this example, the load cellis converting a value of weight from 0 to 500 pounds into a 0- 10 VDC output. The 0 - 10 VDC load cell output is connected

to the input of an S7-200 PLC analog expansion module. Theanalog value applied to the PLC can be used in various ways.

For instance, the actual weight can be compared to a desiredweight for a package or group of packages.

This example can be expanded to include a conveyor systemwith a gate to direct packages of varying weight. As packagesmove along the conveyor they are weighed. A package thatweighs at or greater than a specified value is routed along one

conveyor path. A package that weighs less than a specifiedvalue is routed along another conveyor path, where it will laterbe inspected for missing contents. All of this functionality canbe controlled by an S7-200 PLC.


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Analog Outputs Analog outputs are used in applications requiring controlcapability of field devices which respond to continuously varyinvoltage or current levels. For example, analog outputs may beused as a variable reference for control valves, chart recorderselectric motor drives, analog meters, and pressure transducers

Like analog inputs, analog outputs are generally connected

to a controlling device through a transducer. The transducertakes the voltage signal and, depending on the requirement,amplifies, reduces, or changes it into another signal whichcontrols the device. In the following example, a 0 - 10 VDCsignal controls a 0 - 500 Lbs. scale analog meter.


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Timers

Timersare devices that count increments of time. Traffic lightsare one example where timers are used. In this example timersare used to control the length of time between signal changes.

Timers are represented by boxes in ladder logic. When a timerreceives an enable, the timer starts to time. The timer comparesits current time with the preset time. The output of the timeris a logic 0 as long as the current time is less than the presettime. When the current time is greater than the preset time, thetimer output is a logic 1. S7-200 uses three types of timers: On-Delay (TON), Retentive On-Delay (TONR), and Off-Delay (TOF).

S7-200 Timers S7-200 timersare provided with resolutions of 1 millisecond,10 milliseconds, and 100 milliseconds. The maximum value ofthese timers is 32.767 seconds, 327.67 seconds, and 3276.7seconds, respectively. By adding program elements, logic canbe programmed for much greater time intervals.


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Hard-Wired Timing Circuit Timers used with PLCs can be compared to timing circuits usein hard-wired control line diagrams. In the following example,a normally open (NO) switch (S1) is used with a timer (TR1).For this example, the timer has been set for 5 seconds. WhenS1 closes, TR1 begins timing. When 5 seconds have elapsed,TR1 will close its associated normally open TR1 contacts,

illuminating pilot light PL1. When S1 opens, de-energizing TR1,

the TR1 contacts open, immediately extinguishing PL1.

This type of timer is referred to as an on-delay timer. The termon-delay indicates that once a timer receives an enable signaa preset amount of time must pass before the timers outputcoil (TR1) turns on.

On-Delay Timer (TON) The previous example illustrated how a hardware on-delay timworks. The corresponding software function in an S7-200 PLC the On-Delay Timer (TON)shown below.

When the On-Delay Timer (TON) receives an enable (logic 1) at

its input (IN), a predetermined amount of time (preset time - Ppasses before the timer bit (T-bit) turns on. The T-bit is a logicfunction internal to the timer and is not shown on the symbol.The timer resets to the accumulated time to zero when theenabling input goes to a logic 0.


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In the following simple timer example, a switch is connected toinput I0.3, and a light is connected to output Q0.1.

When the switch closes, the PLCs input 4 becomes a logic1, the I0.3 contact closes, and timer T37 begins timing. T37has a time base of 100 ms (0.1 seconds). The preset time (PT)value has been set to 150. This is equivalent to 15 seconds(0.1 x 150 ). 15 seconds after the input switch closes, the timeroutput becomes a logic 1, the T37 contact closes, output Q0.1becomes a logic 1, and the light turns on. If the switch were

opened before 15 seconds has passed, then re-closed, thetimer would again begin timing at 0. Because this type of timer

does not retain its accumulated time when its input (IN) goes tologic 0, it is said to be non-retentive.

T37

150

I0.3

Q0.1

TON

T37

IN

PT


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A small sample of the flexibility of PLCs is shown in thefollowing program logic. By reprogramming the T37 contact asa normally closed contact, the function of the circuit is changeto cause the indicator light to turn off only when the timer timeout. This function change was accomplished without changingor rewiring I/O devices.

T37

150

I0.3

Q0.1

TON

T37

IN

PT

Retentive On-Delay Timer The Retentive On-Delay Timer (TONR)functions in a similar(TONR) manner to the On-Delay Timer (TON). Just like the On-Delay

timer (TON), the Retentive On-Delay Timer (TONR) times as lonas the enabling input is on, but does not reset when the input

goes off. The timer must be reset with a RESET (R)instruction


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The same example used with the On-Delay Timer (TON) isshown below with the Retentive On-Delay timer (TONR).When the switch connected to input I0.3 closes, I0.3 contactcloses, and timer T5 begins timing. If, for example, after 10seconds input I0.3 turns off, the timer stops. When input I0.3

turns on again, the timer begins timing at 10 seconds. The lightconnected to O0.1 turns on 5 seconds after input I0.3 has been

closed for the second time.

A RESET (R)instruction has been added to the logic. TheRESET (R) function allows the accumulated time of theRetentive On-delay Timer (TONR) to be reset to zero. In thisexample, the RESET (R) function turns on and resets the timer

every time contact I0.2 closes.

T5

T5

150

I0.3

I0.2

Q0.1

R

TONR

T5

IN

PT

Off-Delay Timer (TOF) The Off-Delay Timer (TOF)is used to delay turning an outputoff for a fixed period of time after the input turns off. When theenabling bit turns on, the timer bit turns on immediately, and

the time value is set to 0. When the input turns off, the timertimes until the preset time has elapsed. At that time, the timerbit turns off.

TOF

TXXX

IN

PT


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S7-200 Timer Numbers S7-200 PLCs have 256 available timer numbers. The specificT number chosen for the timer determines its time base andwhich type of timer it is (TON, TONR, or TOF).

Timer Example In the following example, a tank is filled with two chemicals, thsolution is mixed, and the tank is drained.

When the Start button is pressed, input I0.0 turns on, and theprogram starts pump 1, controlled by output Q0.0. Pump 1 runfor 5 seconds, adding the first chemical to the tank, then shuts

off. The program then starts pump 2, controlled by output Q0.1Pump 2 runs for 3 seconds adding the second chemical to thetank. After 3 seconds pump 2 shuts off. The program then starthe mixer motor, connected to output Q0.2 and mixes the twochemicals for 60 seconds. Next, the program opens the drainvalve, controlled by output Q0.3, and starts pump 3 controlledby output Q0.4. Pump 3 shuts off after 8 seconds and theprocess stops. A manual Stop switch is also provided at input

I0.1.


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Review 5

1. PLCs convert analog signals into a ____________ formatfor processing.

2. Three types of timers available in the S7-200 are On-

Delay, __________ On-Delay, and ____-Delay.

3. The maximum time available with a 100 millisecondtime base timer is ____________ seconds.

4. A count of 25 on a 10 millisecond time base timerrepresents a time of _______ milliseconds.

5. There are _______ timer numbers available in the S7-200 PLC.


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Counters

Countersused in PLCs serve the same function as mechanicacounters. Counters compare an accumulated value to a presetvalue to control circuit functions. Counters can be used to initiaan operation when a count is reached or to prevent an operatio

from occuring until a count has been reached.

A bottling machine, for example, may use a counter to countbottles into groups of six for packaging.

Counters are represented in an S7-200 program by boxesin ladder logic. Counters increment or decrement one counteach time the input transitions from off (logic 0) to on (logic 1).Counters are reset when a RESET instruction is executed. S7-200 uses three types of counters: Count Up Counter (CTU),Count Down Counter (CTD), and Count Up/Down Counter(CTUD).

Count Up/DownCount Up Count Down

PV PV

R LD

PV

CU CDCD

CU

R

CTU CTD CTUD

XXX XXX XXX


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S7-200 Counters There are 256 counters available in the S7-200, numbered C0through C255. The same number cannot be assigned to morethan one counter. For example, if an up counter is assignednumber 45, a down counter cannot also be assigned number45. The maximum count value of a counter is 32,767.

Count Up Counter (CTU) The Count Up Counter (CTU) counts up from the current value

each time the count up (CU) input goes from off to on. Whenthe current value is greater than or equal to the preset value(PV), the counter bit for designated counter is a logic 1. Thecourse resets when the reset (R) input turns on. The counterstops counting when it reaches its maximum value of 32,767.

PV

R

CU CTU

Cxx

Count Down Counter (CTD) The Count Down Counter (CTD) counts down from the currentvalue each time the count down (CD) input goes from off toon. When the current value is equal to zero, the counter bit fordesignated counter is a logic 1. The counter stops counting atzero. The counter resets and loads the current value with thepreset value (PV) when the load input (LD) turns on.

PV

LD

CD CTD

Cxx


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Count Up/Down Counter The Count Up/Down Counter (CTUD) counts up each time the(CTUD) count up (CU) input turns on and counts down each time the

count down input (CD) turns on. When the current value isequal to or greater than the preset value (PV), the counter bit fothe designated counter is a logic 1. Otherwise, the counter bitis a logic 0. If the count reaches 32,767, the next count change

the current value to -32,768. The counter current value is reset

to zero when the reset (R) input turns or when the Resetinstruction is executed.

PV

CU

CD

R

CTUD

Cxx

Counter Example A counter might be used to keep track of the number ofvehicles in a parking lot. As vehicles enter the lot through anentrance gate, the counter counts up. As vehicles exit the lotthrough an exit gate, the counter counts down. When the lot is

full a sign at the entrance gate turns on indicating the lot is full


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Count Up/down Counter C48 is used in this example. A switch,connected to the entrance gate is wired to input I0.0. A switch,connected to the exit gate, is wired to input I0.1. A reset switch,located at the collection booth, is wired to input I0.2.

The parking lot has 150 parking spaces. This value has beenstored in the preset value (PV). The counter output controls

output Q0.1. This output is connected to a Parking Lot Fullsign.

When a car enters the lot, the entrance gate opens. Input I0.0transitions from a logic 0 to a logic 1, increasing the count byone. When a car leaves the lot, the exit gate opens. Input I0.1

transitions from a logic 0 to a logic 1, decreasing the count by 1.

When the count reaches 150, output Q0.1 turns on and theParking Lot Full sign illuminates. When a car exits, decreasingthe count to 149, the sign turns off.

C48

CTUDCU

I0.0

I0.1

I0.2

CD

R

PV150

Q0.1C48


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7

High-Speed Instructions

As discussed earlier, PLCs have a scan time. The scan timedepends on the size of the program, the number of I/Os, andthe amount of communication required. Events may occur inan application that require a response from the PLC before

the scan cycle is complete. For these applications high-speedinstructions can be used.

High-Speed Counters A high-speed counteris represented by two boxes in ladderlogic. One box is the High-Speed Counter Definition (HDEF)

instruction and the other box is the High-Speed Counter(HSC)instruction.

CPU 221 and CPU 222 support four high-speed counters(HSC0, HSC3, HSC4, HSC5). CPU 224, CPU 224XP, and

CPU 226 support six high-speed counters (HSC0, HSC1, HSC2HSC3, HSC4, HSC5).


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Definition Boxes and The High-Speed Counter Definition (HDEF) instructionassignsHigh-Speed Counters the operating mode to a specific high-speed counter (HSCx).

The mode selection defines the clock, direction, start, andreset functions of the high-speed counter. High-speed counterscan be defined by the definition box to operate in any of the

12 available modes. Not all counters can operate in all of theavailable modes, however. Refer to the S7-200 System Manual

for definitions available for each counter.

The High-Speed Counter (HSC) instruction configures andcontrols a specific high-speed counter based upon the state ofthe special HSC bits. The N parameter specifies the high-speedcounter number. Each counter has dedicated inputs for clocks,

direction control, reset, and start where these functions aresupported.

Positioning Example Positioningis one example of an application that can usehigh-speed counters. In the following illustration, a motor is

connected through a starter to a PLC output. The motor shaftis connected to an encoder and a positioning actuator. Theencoder emits a series of pulses as the motor turns.

In this example, the program will move an object from position1 to position 6. This example uses an encoder that generates600 pulses per revolution, and it takes 1000 motor revolutionsto move the object from one position to another. To move theobject from position 1 to position 6 (5 positions) would take5000 motor revolutions. For that move, the counter would count

up 30,000 counts (5000 revolutions x 600 pulses per revolution)and stop the motor.

1 2 3 4 5 6 7 8 9 100

MotorEncoder

Starter


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7

Interrupts The S7-200 PLC also incorporates instructions for use withinterrupts. Interruptsare used to initiate a specific, short PLCprogram segment, called an interrupt routine, when an internaor external event occurs. Once the last instruction of theinterrupt routine has been executed, control is returned to themain program. Interrupt processing allows the PLC to respond

quickly to special events.

PTO Pulse Train Output (PTO)is used to provide a series of pulsesto an output device, such as a stepper motor driver. The PTOprovides a square wave output for a specified number of pulseand a specified cycle time. The number of pulses can be from1 to 4,294,967,295 pulses. PTOs have a 50% duty cycle. Thismeans the pulse is off for the same amount of time that it is

on. The number of pulses and the cycle time can be changedwith an interrupt. In the following example, each pulse is onfor 500 ms and off for 500 ms. After four pulses, an interruptoccurs which changes the cycle time to 1000 ms.

Q0.0

4 Pulses

500 milliseconds Each

4 Pulses

1000 milliseconds Each

Interrupt

Occurs

PWM The Pulse Width Modulation (PWM) functionprovides afixed cycle time with a variable duty cycle time. When the pulswidth is equal to the cycle time, the duty cycle is 100% andthe output is turned on continuously. In the following examplethe output has a 10% duty cycle (on 10% off 90%). After an

interrupt, the cycle switches to a 50% duty cycle (on 50%, off50%).

Q0.0

On OnOff Off

10%

Duty Cycle

50%

Duty Cycle

The PWM function can be used to provide a programmable

or adjustable control of machine timing. This allows machineoperation to be varied to compensate for product variations ormechanical wear.

And Much More The instructions listed in this section are only examples ofthe types of instructions available for S7-200 PLCs. The fullinstruction set includes a much broader range of capabilities.Refer to the S7-200 System Manual for additional information.


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Specialized Expansion Modules

In addition to I/O modules, expansion modules are availablefor the S7-200 that measure temperature, control positioningapplications, and provide various communication functions.

EM 241 In any complex system, communication is essential. Modemsare electronic devices used for sending and receiving dataover long distances. The EM 241is an expansion module thatsupports communication between an S7-200 PLC and STEP 7Micro/WIN via a modem.

The EM 241 provides an international telephone line interface,supports sending numeric and text paging messages, as wellas SMS (Short Message Service) messages to cellular phones.

This is useful for remote diagnostics and maintenance, machinecontrol, alarm systems, and general communication functions.

In addition to CPU-to-CPU communication via a telephone line,the EM 241 also supports the ModBus RTU protocol. Protocols

are rules that identify how devices should communicate witheach other. ModBus RTU is a protocol originally developedby MODICON, which is now part of Schneider Automation.ModBus RTU has been widely used by other companies.

CP 243-1, CP 243-1 IT Industrial Ethernet provides a proven means of networking

computers and a variety of intelligent devices. CP 243-1andCP 243-1 ITare communication processors used to connect theS7-200 system to Industrial Ethernet.


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Ethernet Communications

CP 243-1 Ethernet

CP 243-1 IT Internet

The S7-200 can be remotely configured, programmed, anddiagnosed via Industrial Ethernet using STEP 7 Micro/WIN.The S7-200 can also communicate with other S7-200, S7-300,and S7-400 PLCs and a variety of other devices using IndustriaEthernet.

The IT functions of the CP 243-1 IT Internet module simplify thprocess of setting up a control system that can email diagnostinformation or transfer files using Internet protocols.

EM 277 Information flow between intelligent devices such as PLCs,computers, variable speed drives, actuators, and sensors isoften accomplished through a local area network (LAN). LANsare used in office, manufacturing, and industrial areas.

In the past, these networks were often proprietary systemsdesigned to a specific vendors standards. Siemens hasbeen a leader in pushing the trend to open systems basedupon international standards developed through industryassociations. PROFIBUS-DP and Actuator Sensor Interface(AS-i) are examples of these open networks.

The PROFIBUS-DP EM 277 moduleallows connection ofthe S7-200 CPU to a PROFIBUS-DP network as a slave. TheCP 243-2 Communication Processor allows communicationbetween AS-i devices and an S7-200.


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PROFIBUS DP PROFIBUS DPis an open bus standard for a wide rangeof applications in various manufacturing and automationprocesses. PROFIBUS DP works at the field device level toallow communication of a broad range of intelligent devices.Through PROFIBUS DP the features of S7-200 PLCs can

be used to their full extent within a distributed system. Anadvantage to PROFIBUS DP is the ability to communicate

between PROFIBUS DP devices of different vendors. Thisprovides uniform communication between all SIMATIC deviceson the PROFIBUS DP network as well as devices from othermanufacturers.

AS-i Actuator Sensor Interface (AS-i or AS-Interface)is a systemfor networking field devices such as sensors and actuators withcontrol and operator interface devices. Until recently, extensive

parallel control wiring was needed to connect sensors to thecontrolling device. AS-i replaces complex wiring with a simple2-core cable. The cable is designed so that devices can only beconnected correctly. Multiple can be connected to the cable.


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Use of the AS-i field bus allows an S7-200 PLC to be easilyconnected to a variety devices from multiple equipmentsuppliers.

EM 253 Position control describes a range of applications that involvemovement with varying degrees of precision. Rotary tables antraversing cars are examples where objects are moved fromone position during a products manufacturing process.

The EM 253is a positioning module designed for single acces

open loop position control through use of stepper motor orservo motor. The EM 253 interfaces between an S7-200 PLCand the stepper/servo motors power control module.

Power ModuleServo/Stepper

Stepper Motor

Servo Motor

Control

Actual Value

S7-200 with EM 253


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EM 253 Features Features of the module include:

High-speed control with a range of 12 - 200,000 pulse persecond

Jerk (S curve) or linear acceleration/deceleration

Configurable measuring system to enter data asengineering units (such as inches or centimeters) ornumber of pulses

Configurable backlash compensation

Supports absolute, relative, and manual methods ofposition control

Continuous operation

Provides up to 25 motion profiles with up to 4 speedchanges per profile

Four different reference-point seek modes, with a choice

of the starting seek direction and final approach directionfor each sequence

S7-200 Web Site For more information and sales support on the S7-200 visit ourweb site at:

http://www.automation.siemens.com/_en/s7-200/Products/index.htm.


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7

Review 6

1. There are______ counters available in an S7-200 PLC.

2. Three types of counters used in the S7-200 are____________ , ____________ , and ____________ .

3. Counters can count to a maximum of __________ .

4. Depending on the counter, there are up to ____ modesavailable on high-speed counters.

6. The _________ allows communication between AS-idevices and an S7-200.

7. The _________ is a single axis position control module.


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Review Answers

Review 1 1) a: input module, b: CPU, c: output module, d: programmingdevice, e: operator interface; 2) 2; 3) 16; 4) 1010, 0001 0000, A.

Review 2 1) discrete; 2) discrete; 3) CPU; 4) Ladder logic; 5) program;6) program, data, configurable parameter; 7) 1024; 8) firmware; 9

e; 10) RS-485.

Review 3 1) 221, 222, 224, 224XP, 226; 2) b; 3) 2, 7; 4) 8, 6; 5) 14, 10;6) Q0.3; 7) DIN.

Review 4 1) a: box, b: contact, c: coil; 2) AND Function - a: 0, b: 0, c: 0, d: 1Or Function - e: 0, f: 1, g: 1, h: 1; 3) I0.1, I0.0, Q0.0.

Review 5 1) digital; 2) Retentive, Off; 3) 3276.7 seconds; 4) 250; 5) 256.

Review 6 1) 256; 2) Count Up Counter (CTU), Count Down Counter (CTD),Count Up/Down Counter (CTUD); 3) 32,767; 4) 12; 5) CP 243-2Communication Processor; 6) EM 253.


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Final Exam

The final exam is intended to be a learning tool. The bookmay be used during the exam. A tear-out answer sheet isprovided. After completing the test, mail the answer sheet in fograding. A grade of 70% or better is passing. Upon successful

completion of the test a certificate will be issued.

1. The component of a PLC that stores and executes themain program is the ______ .

a. CPU b. Input/Output module

c. Programming device d. Operator interface

2. One byte is made up of _________ .

a. 2 bits b. 8 bits c. 16 bits d. 32 bits

3. The binary equivalent of a decimal 5 is _____ .

a. 11 b. 100 c. 101 d. 111

4. An input that is either on or off is a/an ____________ input

a. analog b. discrete c. RTD d. thermocouple

5. A programming language that uses symbols resemblingelements used in hard-wired control line diagrams is

referred to as ____________ .

a. ladder logic b. statement list c. function blocks d. a flow chart

6. A type of memory that can be read from but not written tis _________ memory.

a. RAM b. ROM

c. R/W d. Read-Write


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7. A USB/PPI Multi-Master cable connects a personalcomputers USB interface to a/an _________ connector onan S7-200 CPU.

a. RS-485 b. RS-232 c. Ethernet d. PROFIBUS-DP

8. The CPU 224 AC/DC/RELAY has ____________ .

a. 8 DC inputs and 10 relay outputs b. 8 AC inputs and 6 relay outputs c. 14 DC inputs and 14 relay outputs d. 14 DC inputs and 10 relay outputs

9. CPU 224 will accept up to ____________ expansionmodules.

a. none b. 7

c. 10 d. 30

10. The S7-222 has the ability to store _________ bytes ofuser data.

a. 1024 b. 8192

c. 2048 d. 10240

11. Which of the following is not part of a PLC scan?

a. Read Inputs b. Execute Program c. Reset All Timers d. Update Outputs

12. The address designation for output four of an S7-200 is________ .

a. I0.4 b. I0.3 c. Q0.3 d. Q0.4

13. CPU 221 and CPU 222 provide ____________ high-speedcounters .

a. two b. three

c. four d. five

14. The maximum value of an S7-200 timer with a resolutionof 1 millisecond is ____________ seconds.

a. 3.2767 b. 32.767 c. 327.67 d. 3276.7


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15. An S7-200 timer with a time base of 100 ms can count toa maximum value of ____________ seconds.

a. 3.2767 b. 32.767 c. 327.67 d. 3276.7

16. The time base of TON 32 is ____________ ms.

a. 0.1 b. 10 c. 1 d. 100

17. The maximum count of an S7-200 Count Up Counter (CTis _________.

a. 32,767 b. 65,534 c. 98,301 d. 1,000,000

18. A/An ________ instruction is used to assign a mode to a

high-speed counter.

a. CTUD b. Interrupt c. HSC d. HDEF

19. The ______ module allows connection of the S7-200 CPUto a PROFIBUS-DP network as a slave.

a. EM 277 b. EM241 c. CP 243-1 d. CP 243-1 IT

20. ____________ is used to temporarily override input oroutput status in order to test and debug the program or

system.

a. Transmitting b. Forcing c. Interrupting d. Holding


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quickSTEP Online Courses

quickSTEP online courses are available athttp://www.sea.siemens.com/step.

The quickSTEP training site is divided into three sections:

Courses, Downloads, and a Glossary. Online coursesinclude reviews, a final exam, the ability to print a certificateof completion, and the opportunity to register in the Sales& Distributor training database to maintain a record of youraccomplishments.

From this site the complete text of all STEP courses can bedownloaded in PDF format. These files contain the most recentchanges and updates to the STEP courses.

A unique feature of the quickSTEP site is our pictorial glossary.

The pictorial glossary can be accessed from anywhere withina quickSTEP course. This enables the student to look up anunfamiliar word without leaving the current work area.

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