Simatic S5 PLC
The Simatic S5 PLC is an automation
Automation is the use of control systems and information technologies to reduce the need for human work in the production of goods and services. In the scope of industrialization, automation is a step beyond mechanization...

 system based on Programmable Logic Controller
Programmable logic controller
A programmable logic controller or programmable controller is a digital computer used for automation of electromechanical processes, such as control of machinery on factory assembly lines, amusement rides, or light fixtures. PLCs are used in many industries and machines...

s. It is manufactured and sold by Siemens AG
Siemens AG
Siemens AG is a German multinational conglomerate company headquartered in Munich, Germany. It is the largest Europe-based electronics and electrical engineering company....

. Such automation systems control
Systems control
Systems control, in a communications system, is the control and implementation of a set of functions that:# prevent or eliminate degradation of any part of the system,# initiate immediate response to demands that are placed on the system,...

 process equipment and machinery used in manufacturing. This product line
Product lining
Product lining is the marketing strategy of offering for sale several related products. Unlike product bundling, where several products are combined into one, lining involves offering several related products individually. A line can comprise related products of various sizes, types, colors,...

 is considered obsolete, as the manufacturer has since replaced it with their newer Simatic S7 PLC. However, the S5 PLC still has a huge installation base in factories around the world. Most automation systems integrators still have the ability to provide support for the platform.


The S5 line comes in the 90U, 95U,101U,100U, 105, 115U, 135U, and 155U chassis styles.Higher the number, the more sophisticated and more expensive the system. Within each chassis style, several CPUs are available, with varying speed, memory, and capabilities. Some systems provide redundant CPU operation for ultra-high-reliability control, as used in pharmaceutical
Pharmaceutical company
The pharmaceutical industry develops, produces, and markets drugs licensed for use as medications. Pharmaceutical companies are allowed to deal in generic and/or brand medications and medical devices...

Manufacturing is the use of machines, tools and labor to produce goods for use or sale. The term may refer to a range of human activity, from handicraft to high tech, but is most commonly applied to industrial production, in which raw materials are transformed into finished goods on a large scale...

, for example.

Each chassis consists of a power supply
Power supply
A power supply is a device that supplies electrical energy to one or more electric loads. The term is most commonly applied to devices that convert one form of electrical energy to another, though it may also refer to devices that convert another form of energy to electrical energy...

, and a backplane with slots for the addition of various option boards. Available options include serial and Ethernet communications, digital input and output cards, analog signal processing
Analog signal processing
Analog signal processing is any signal processing conducted on analog signals by analog means. "Analog" indicates something that is mathematically represented as a set of continuous values. This differs from "digital" which uses a series of discrete quantities to represent signal...

 boards, counter cards, and other specialized interface and function modules.


The S5 product line is usually programmed with a PC based software programming tool called Step 5. Step 5 is used for programming, testing, and commissioning, and for documentation of programs for S5 PLCs.

The original Step 5 versions ran on the CPM operating system
CP/M was a mass-market operating system created for Intel 8080/85 based microcomputers by Gary Kildall of Digital Research, Inc...

. Later versions ran on MS-DOS
MS-DOS is an operating system for x86-based personal computers. It was the most commonly used member of the DOS family of operating systems, and was the main operating system for IBM PC compatible personal computers during the 1980s to the mid 1990s, until it was gradually superseded by operating...

, and then versions of Windows through Windows XP
Windows XP
Windows XP is an operating system produced by Microsoft for use on personal computers, including home and business desktops, laptops and media centers. First released to computer manufacturers on August 24, 2001, it is the second most popular version of Windows, based on installed user base...

. The final version of Step 5 is version 7.2. No further development of this product line has occurred since that time, due to its announced obsolescence.

In addition to Step5, Siemens offered a proprietary State logic
State logic
A state logic control system is a programming method created for PLCs.A state logic control system uses a state transition diagram as a model of reality, thus using the fundamentals of finite-state machine theory as the basis of a programming language...

 programming package called Graph5. Graph5 is a sequential programming language
Programming language
A programming language is an artificial language designed to communicate instructions to a machine, particularly a computer. Programming languages can be used to create programs that control the behavior of a machine and/or to express algorithms precisely....

 intended for use on machines that normally run through a series of discrete steps. It simulates a State machine on the S5 platform.

Several third-party programming environments have been released for the S5. Most closely emulate Step5, some adding macros and other minor enhancements, others functioning drastically differently than Step5. One allows Step5 programs to be cross-compiled to and from the C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....

 programming language and BASIC
BASIC is a family of general-purpose, high-level programming languages whose design philosophy emphasizes ease of use - the name is an acronym from Beginner's All-purpose Symbolic Instruction Code....


Structured programming

STEP 5 allows the creation of structured or unstructured programming, from simple AND/OR operations up to complex subroutines. A STEP 5 program may, therefore, contain thousands of statements.

To maintain maximum transparency, STEP 5 offers a number of structuring facilities:
  • Block technique - A linear operation sequence is divided into sections and packed into individual blocks.
  • Segments - Within blocks, fine structuring is possible by programming subtasks in individual segments.
  • Comments - Both a complete program as well as individual blocks or segments and individual statements can be directly provided with comments.

Methods of representation

STEP 5 programs can be represented in three different ways:
  • Statement List (STL) - The program consists of a sequence of mnemonic codes of the commands executed one after another by the PLC.
  • Ladder Diagram
    Ladder logic
    Ladder logic is a programming language that represents a program by a graphical diagram based on the circuit diagrams of relay logic hardware. It is primarily used to develop software for programmable logic controllers used in industrial control applications...

     (LAD) - Graphical representation of the automation task with symbols of the circuit diagram
    Circuit diagram
    A circuit diagram is a simplified conventional graphical representation of an electrical circuit...

  • Function Block Diagram
    Function block diagram
    A function block diagram is a block diagram that describes a function between input variables and output variables. A function is described as a set of elementary blocks. Input and output variables are connected to blocks by connection lines...

     (FBD) - Graphical representation of the automation task with symbols to DIN 40700/ DIN 40719.

Absolute or symbolic designations can be used for operands with all three methods of representation.

In LAD and FBD complex functions and function block calls can be entered via function key
Function key
A function key is a key on a computer or terminal keyboard which can be programmed so as to cause an operating system command interpreter or application program to perform certain actions...

s. They are displayed on the screen as graphical symbols.


Five types of blocks are available:
  • Organization blocks (OB) - for managing the control program
  • Programming blocks (PB) - contain the control program structured according to functional or process-oriented characteristics
  • Sequence blocks (SB) - for programming sequential controls
  • Function blocks (FB) - contain frequently occurring and particularly complex program parts
  • Data blocks (DB) - for storing data required for processing the control program.

Some S5 PLCs also have block types FX (Extended Function Blocks), and DX(Extended Data Blocks); these are not distinct block types, but rather are another set of available blocks due to the CPU having more memory and addressing space.


STEP 5 differentiates between three types of operations:
  • Basic operations, (e.g. linking, saving, loading & transferring, counting, comparing, arithmetic operations, module operations) - These can be performed in all three representations.
  • Supplementary operations and complex functions, (e.g. substitution statements, testing functions, word-by-word logic operations, decrement/increment and jump functions.) - These can only be executed in STL.
  • System operations (direct access the operating system
    Operating system
    An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...

    ) - These can only be executed in STL.

Additional functions

  • Saving user-specific project settings
  • Symbol editor
  • Automatic generation and updating of cross-reference
    A cross-reference is an instance within a document which refers to related or synonymous information elsewhere, usually within the same work. To cross-reference or to cross-refer is to make such connections. The term "cross-reference" is often abbreviated as x-ref, xref, or, in computer science,...

  • Comparison of user programs
  • Transferring blocks to EPROM
    An EPROM , or erasable programmable read only memory, is a type of memory chip that retains its data when its power supply is switched off. In other words, it is non-volatile. It is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages...

     and EEPROM
    EEPROM stands for Electrically Erasable Programmable Read-Only Memory and is a type of non-volatile memory used in computers and other electronic devices to store small amounts of data that must be saved when power is removed, e.g., calibration...

    memory modules for programmable controllers
  • Rewiring inputs, outputs, flags, timers and counters
  • Testing and service functions for startup and maintenance

External references

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.