Simatic

SIMATIC is a series of programmable logic controller and automation systems, developed by Siemens. Introduced in 1958, the series has gone through four major generations, the latest being the SIMATIC S7 generation. The series is intended for industrial automation and production.

The name SIMATIC is a registered trademark of Siemens. It is a portmanteau of "Siemens" and "Automatic".

Function

Siemens SIMATIC S7-300 PLC CPU with three I/O modules attached

As with other programmable logic controllers, SIMATIC devices are intended to separate the control of a machine from the machine's direct operation, in a more lightweight and versatile manner than controls hard-wired for a specific machine. Early SIMATIC devices were transistor-based, intended to replace relays attached and customized to a specific machine. Microprocessors were introduced in 1973, allowing programs similar to those on general-purpose digital computers to be stored and used for machine control.^[1] SIMATIC devices have input and output modules to connect with controlled machines. The programs on the SIMATIC devices respond in real time to inputs from sensors on the controlled machines, and send output signals to actuators on the machines that direct their subsequent operation.

Depending on the device and its connection modules, signals may be a simple binary value ("high" or "low") or more complex. More complex inputs, outputs, and calculations were also supported as the SIMATIC line developed. For example, the SIMATIC 505 could handle floating point quantities and trigonometric functions.^[2]

History

Siemens Simatic N

On April 2, 1958 the name Simatic (composed of "Siemens" and "Automatic") was registered with the German Patent and Trademark Office (DIN) as a registered trademark of the company Siemens.

A year later, in 1959, the Simatic G^[3] was launched on the market, a system that could replace relay logic with a hard-wired programmed logic controller (based on the use of Germanium transistors). The system was launched under the name "Building-Block System for Solid-State Controls".

In 1964, the Simatic N (1964) was launched (hard-wired programmed logic controller) - based on Silicon transistors.

In 1973, the Simatic S3 was launched, the first microprocessor-based Simatic system that implemented programmable logic.^[4]

In 1979, the Simatic S5 series was launched, a series that was maintained until 2000. Automation systems based on Simatic S5 are still functional worldwide. S5 systems were programmed using the STEP 5 software system. In 1984 the Simatic S5 U (universal) programmable controller series is introduced.

In 1994, the Simatic S7 series was launched, a series based mainly on the S7-200 controllers (dedicated to simple automation systems), S7-300 (suitable for almost any automation system) and S7-400 (dedicated to large and very large automation projects). All controllers in these series allow networking, especially in Profibus or Industrial Ethernet networks.

Siemens Simatic S7-1500

In 1996 Siemens presented the concept of "Totally Integrated Automation", initially a concept referring to the interconnectivity of automation equipment.^[5]

In 2009, the S7-1200 series of PLCs was launched, a series that replaced the S7-200 series.

In 2011, the TIA Portal (Totally Integrated Automation Portal) software package was also launched, a software platform dedicated to the complex programming of automation systems.

In 2013, the S7-1500 series appeared on the market, a new generation of programmable logic controllers intended to replace the S7-300 and S7-400 series over time.

S7-1200 G2, a second generation of the S7-1200, was launched in December 2024.

Controllers

SIMATIC control systems (PLC) are designed to automate as much of the control of industrial plants as possible. Through the system inputs and outputs, it can monitor and control process elements (operation flow, mechanical element status, temperature, pressure) reducing the need for continuous supervision by a human operator.

The operating logic is stored in the form of a software program in the memory of a Central Processing Unit type control system. The automation system is modular and, in addition to the CPU, can be equipped with various digital and/or analog peripheral modules, as well as intelligent control modules. The modules can be configured centrally (mounted in close proximity to the CPU unit) or decentralized, close to the controlled plant. The range of controllers extends from small, compact controllers to high-performance PLC systems. What all Simatic controllers have in common is their robustness against electromagnetic interference (e.g. Simatic-S7 complies with the requirements of Directive 2014/30/EU on electromagnetic compatibility and climatic stress - e.g. 0 to + 60 °C ambient temperature during operation). Simatic is programmed using STEP 7 (formerly STEP 5) programming software or software from third-party manufacturers.

Siemens has developed more product lines to date. First versions were hard-wired, the first processor based series being SIMATIC S3

SIMATIC S3

(starting from 1973)

S3 was based on hard-wired logic SIMATIC C3.

• Example: Simatic S3-111

Simatic S5

Siemens S5-95U-CPU

(1979 - 2000)

The S5 line was sold in various chassis configurations. Within each chassis style, several CPUs were available, with varying speed, memory, and capabilities. Some systems provided "fail-safe" control, used for safety applications or redundant CPU operation for ultra-high-reliability control, as used in pharmaceutical manufacturing, for example.

Each configuration was built starting from the central unit to which the various input and output modules, communication or modules for special functions were attached. The compact variants were configured by directly coupling the modules onto the support rail, the complex variants were configured by mounting modular boards in a dedicated drawer.

• Simatic S5-010 – Modular PLC system
  • Simatic S5-010K – Variant for injection molding machines (Kunststoffspritz).
  • Simatic S5-010W – Variant for machine tools (Werkzeugmaschinen) or positioning systems.

• Simatic S5-90U – Compact control units
  • Example: 6ES5090-8MA0x / S5-90 / 4 kByte RAM / Integrated 230 V AC power supply, 10 binary inputs, 6 relay outputs directly on the CPU

• Simatic S5-95^[6] – Compact control units
  • Simatic S5-95F – Failsafe version - integrated safety functions
  • Simatic S5-95U^[7] – universal version

Simatic S5-100U CPU103, PLC central unit

• Simatic S5-100U^[8] – Modular unit

• Simatic S5-101 – Compact unit
  • Simatic S5-101R^[9] – Programming in LAD language only
  • Simatic S5-101U^[10] – Programming in AWL/STL, LAD and CSF/FBD; Expansion possible with expansion module

• Simatic S5-105R – Modular system in 19-inch drawer. Programming only in LAD ("R" stands for Relay - programming in LAD = relay diagram)

• Simatic S5-110 – Modular system
  • Simatic S5-110A – Modular
  • Simatic S5-110F^[11] – Failsafe version - integrated safety functions
  • Simatic S5-110S – Modular, drawer mounting with external I/O bus

• Simatic S5-115 – Modular system, fanless central unit, (fans for certain drawer types), different memory capacities depending on version, expandable memory with plug-in modules
  • Simatic S5-115F – Failsafe version - integrated safety functions
  • Simatic S5-115H – Redundant version (High Availability)
  • Simatic S5-115U^[12] – Universal version

• Simatic S5-130 – Mid-range modular system (performance-wise)
  • Simatic S5-130A – Robust version (encapsulated modules)
  • Simatic S5-130K – Compact version (cardboard in drawer)
  • Simatic S5-130W – Cardboard in drawer version for industrial process automation

• Simatic S5-135U – Mid-range modular system (performance-wise). The first Simatic system that allows multiprocessor configurations (up to 4 central units in parallel). Each central unit has its own PLC program, its own memory areas, counters and timers. Communication between the processors can be achieved via a common memory area (Dual-Port-RAM) or via data blocks (DB blocks).
  • Ex.: 6ES5 920-3UA1x, 6ES5 921-3UA1x, 6ES5 922-3UA1x, 6ES5 928-3UA1x, 6ES5 928-3UA2x, 6ES5 928-3UB1x, 6ES5 928-3UB2x, ...

• Simatic S5-150 – Modular system with ventilated drawer for complex automation or central coordination systems, introduced on the market in 1980.
  • Simatic S5-150A – Robust design variant (encapsulated modules)
  • Simatic S5-150K – Compact design variant (card boards in drawer)
  • Simatic S5-150S – Drawer design variant (card boards in drawer)
  • Simatic S5-150U – Drawer design variant (card-type boards in the drawer)
  • Ex.: 6ES5 924..., 6ES5 925..., 6ES5 926..., 6ES5 927...

• Simatic S5-155 – Modular system, with ventilated drawer, for complex automation, allows single- or multi-processor configurations.
  • Simatic S5-155H – Redundant version ("High Availability")
  • Simatic S5-155U - Universal version
  • Ex.: 6ES5 946..., 6ES5 947..., 6ES5 948...

Simatic S7 (S7-200, S7-300, S7-400)

(since 1994)

The first entries in the S7 line were released in 1994, available under three performance classes: S7-200, S7-300 and S7-400. The introduction of SIMATIC S7 saw also the release of a new fieldbus standard Profibus, and the pioneer use of industrial Ethernet to facilitate communication between automation devices. The great success of the S7-300 CPU family in particular helped to cement the role of Siemens as one of the global leaders in automation technology. These series are expected to be phased out in 2033.^[13]

Simatic S7-200

(phased-out - SIOS, 2017-07-26)

A series of small (80 mm x 62 mm), fast (0.22 μs binary execution time) PLC modules with an integrated RS 485 interface (PPI Interface = Point to Point Interface).

• for low-complexity automation applications
• Programmable using the Step 7 MicroWin software (originally Step 7 MicroDos).
• Although no longer marketed as such, S7-200 units are still used for the PLC units integrated in the Sinumerik 828D CNC Numerical Controls series.

Simatic S7-300 ^[14]

Siemens Simatic S7-300

Modular PLC system (but there are also some compact CPU units, with integrated Inputs/Outputs). Communication with other devices is possible via the integrated RS 485 (MPI = Multi Point Interface), Profibus, Profinet and Ethernet interfaces.

• modular system, expansion of the number of inputs/outputs by adding modules
• for automation applications of low or medium complexity
• system programming is done using the STEP 7 software package.
• PLC program storage is done on an MMC card inserted in the CPU unit.

The system consists of:

• A CPU unit that also includes communication functions (MPI, Profibus or Profinet, depending on the chosen variant)
• SM modules for connecting inputs and outputs (digital or analog)
• Optional: IM interface modules or SP communication processors for various types of communication buses
• Optional: FM function modules such as high-speed counters, positioning (closed/open loop), PID control, etc.

Simatic S7-300: Control units (extract)

• CPU 312 32 KB working memory, MPI interface; storage medium: MMC card
• CPU 314 128 KB working memory, MPI interface; storage medium: MMC card
• CPU 315-2DP 256 KB working memory, MPI interface, ProfiBus DP master/slave interface; storage medium: MMC card
• CPU 315-2 PN/DP 384 KB working memory, dual interface MPI/PROFIBUS DP master/slave, Ethernet/PROFINET interface with 2-port switch; MMC card
• CPU 317-2 DP 1 MB working memory, MPI interface, PROFIBUS DP master/slave interface; MMC card
• CPU 317-2 PN/DP 1 MB working memory, dual interface MPI/PROFIBUS DP master/slave, Ethernet/PROFINET interface with 2-port switch; MMC card
• CPU 319-3 PN/DP 2 MB working memory, dual interface MPI/PROFIBUS DP master/slave, PROFIBUS DP master/slave, Ethernet/PROFINET interface with 2-port switch; MMC card

Simatic S7-300F

Modular PLC system, based on S7-300, with extended functions for process control in which functional safety ("safety functionality") plays an important role.

• the system allows the achievement of functional safety requirements SIL 1 to SIL 3 according to IEC 61508, PL a to PL e according to EN ISO 13849-1, Cat 1, 2, 3 and 4 according to EN 954-1.
• the system implements the functionality of an S7-300 system, the functional safety functions only extend the possibilities of the system.
• special dedicated input / output modules ("failsafe") may be required to implement the safety functions, which can also be connected together with the usual input / output modules (mixed use).
• the system is programmed using the STEP 7 software package, for safety functions the STEP 7 Distributed Safety extension package is required.

Simatic S7-300 SIPLUS

Modular PLC system, based on S7-300, for use in adverse environmental conditions (-25 ... 60 °C, high humidity, frost, etc.).

Simatic S7-400 ^[15]

Siemens Simatic S7-400, from left to right: PS power supply unit, CPU unit 416-3, IM 460-0 interface module and CP 443-1 communication processor.

Modular PLC system, with dedicated drawer mounting. Communication with other devices is possible via the integrated RS 485 (MPI = Multi Point Interface), Profibus, Profinet and Ethernet interfaces.

• modular system, expansion of the number of inputs / outputs by adding modules in the drawer or distributed periphery.
• for medium and high complexity automation applications.
• system programming is done using the STEP 7 software package
• PLC program storage is done on the card
• allows the use of multiple CPU units in a single system (multi-processor) for complex applications.

The system consists of:

• A CPU unit that also includes communication functions (MPI, Profibus or Profinet, depending on the chosen variant)
• SM modules for connecting inputs and outputs (digital or analog)
• Optional: IM interface modules or SP communication processors for various types of communication buses
• Optional: FM function modules such as high-speed counting, positioning (closed/open loop), PID control, etc.

S7-400H

Redundant S7-400 system, with two central units and the possibility of connecting I/O modules in pairs, for extended availability.

S7-400F / S7-400FH

S7-400 "failsafe" system with safety functions, in single-channel or redundant version.

S7-400F: single-channel, single set of I/O

S7-400FH: redundant, I/O in pairs, switchable or single-channel, I/O in pairs

Simatic WinAC-RTX

SIMATIC WinAC RTX is a SIMATIC software control system, which can be installed on an industrial PC. The I/O modules can be connected via PROFIBUS or PROFINET using the Ethernet interface or PCI expansion cards.

Simatic S7 (S7-1200, S7-1500)

(since 2009)

In April 2009, Siemens initiated a generational change in the Simatic S7 controllers by launching, first, the S7-1200 controller family, then, in 2012, S7-1500.^[16]

Simatic S7-1200

Siemens Simatic S7-1200

(since 2009)

S7-1200^[17] is a family of small (approx. 100 mm × 75 mm), compact PLC units, intended for low-complexity control solutions. It has up to 150 kB of working memory, 2 Mbytes of integrated program memory that can be expanded up to 24 Mbytes and an execution time for bit instructions of approximately 0.1 μs. Communication with other devices is possible via the integrated Profinet and Ethernet interfaces or via optional communication modules.

• modular system, expansion of the number of inputs / outputs by adding modules
• for automation applications of low or medium complexity
• system programming is done using the software package TIA STEP 7 (Totally Integrated Automation Step 7).
• PLC program storage is done internally, on the EEPROM integrated in the module, or on the Simatic Memory Card (SD Card).

The system consists of:

• A CPU unit that also includes Profinet communication functions and a number of digital or analog inputs and outputs.
• Optional: SM modules for expanding the number of inputs and outputs (digital or analog).
• Optional: CM communication modules for various types of communication buses (RS232, ModBus, GPRS, ...).
• Optional: 4-port Ethernet network switch
• Optional: Connection module for SIWAREX weighing systems
• Optional: "Condition Monitoring" module for monitoring drive systems (wear, motor bearings, etc.)

Simatic S7-1200: Control units (extract)

• CPU 1211C DC/DC/DC, AC/DC/relay, DC/DC/relay, 50 KB working memory, 6I/4Q/2AI, expandable with expansion board
• CPU 1212C DC/DC/DC, AC/DC/relay, DC/DC/relay, 75 KB working memory, 8I/6Q/2AI, expandable with expansion board and up to 2 I/O modules
• CPU 1214C DC/DC/DC, AC/DC/relay, DC/DC/relay, 100 KB working memory, 14I/10Q/2AI, expandable with expansion board and up to 8 I/O modules
• CPU 1215C DC/DC/DC, AC/DC/relay, DC/DC/relay, 125 KB working memory, 14I/10Q/2AI/2AQ, expandable with expansion board and up to 8 I/O modules
• CPU 1217C DC/DC/DC, 150 KB working memory, 14I/10Q/2AI/2AQ, expandable with expansion board and up to 8 I/O modules
• CPU 1212FC (failsafe) DC/DC/DC, DC/DC/relay, 100 KB working memory, 8I/6Q/2AI, expandable with expansion board and up to 2 I/O modules (including failsafe I/O)
• CPU 1214FC (failsafe) DC/DC/DC, DC/DC/relay, 125 KB working memory, 14I/10Q/2AI, expandable with expansion board and up to 8 I/O modules (including failsafe I/O)
• CPU 1215FC (failsafe) DC/DC/DC, DC/DC/relay, 150 KB working memory, 14I/10Q/2AI/2AQ, expandable with expansion board and up to 8 I/O modules (including failsafe I/O)

Simatic S7-1200 G2

(since 2024)

The S7-1200 G2, the second generation of programmable controllers in the S7-1200 range, was presented at the Hannover Messe 2024 edition ^[18] and launched on the market in December 2024 - January 2025, together with TIA-Portal v20 ^[19].

The S7-1200 G2 modules are not hardware compatible with those of the first generation. Compared to the first generation S7-1200, the new modules have improvements regarding:

• reduced execution time
• support for ProfiNet communication of Real-Time (RT) and Isochronous Real-Time (IRT) type
• support for Media Redundancy for Planned Duplication (MRPD) and Media Redundancy Protocol (MRP)
• Program memory of up to 300kB, data memory of up to 750kB, working memory of up to 8MB
• support for the use of SIMATIC Motion Library technology objects (TO_SpeedAxis, TO_PositioningAxis, TO_SynchronousAxis, TO_ExternalEncoder, TO_OutputCam, TO_CamTrack, TO_MeasuringInput, TO_Cam, TO_Kinematics)
• SIMATIC Controller Profiling
• Extended functionality regarding data security (event log, support for user and role management)
• Near Field Communication (NFC) connectivity. Allows diagnosis and parameterization of the CPU unit using a phone app (initially only I-OS). In 2025, few months after S7-1200 G2 series launch, the NFC interface was deactivated in a new firmware release.

Simatic S7-1200 G2: Control units (extract)

• CPU 1212C G2 DC/DC/DC, AC/DC/relay, DC/DC/relay, 150 KB program memory, 500kB data memory, 8DI/6DQ, expandable with expansion board
• CPU 1214C G2 DC/DC/DC, AC/DC/relay, DC/DC/relay, 250 KB program memory, 750kB data memory, 14DI/10DQ, expandable with one or two expansion boards
• CPU 1212FC G2 DC/DC/DC, DC/DC/relay, 150 KB program memory, 500kB data memory, 8DI/6DQ, expandable with expansion board
• CPU 1214C G2 DC/DC/DC, AC/DC/relay, DC/DC/relay, 250 KB program memory, 750kB data memory, 14DI/10DQ, expandable with one or two expansion boards

Simatic S7-1500

Siemens Simatic S7-1500

(since 2012)

At the press conference of the 2012 edition of the SPS/IPC/DRIVES trade fair in Nuremberg, Siemens presented the new Simatic S7-1500 controller which should gradually replace the units of the S7-300 and S7-400 series ^[20]. Motion control functions are now integrated into every CPU as standard, only extended functions such as kinematics requiring special PLC units from the S7-1500T series. Functional safety (up to SIL3 according to IEC 62061 and PL-e according to ISO 13849) is available in the failsafe S7-1500F CPU variants. The CPU units are equipped with Profinet interfaces as standard, have an integrated web server and a color display and can be expanded with up to 32 modules in the central drawer.

• modular system, expansion of the number of inputs / outputs by adding modules
• for automation applications of medium to high complexity
• system programming is done using the software package TIA STEP 7 (Totally Integrated Automation Step 7).
• PLC program storage is done on a Simatic Memory Card (SD Card).

Simatic S7-1500: Control units (excerpt)

• CPU 1511-1PN, 150KB Program, 1MB Data 6ES7511-1AK02-0AB0
• CPU 1511-1PN, 300KB Program, 1.5MB Data 6ES7511-1AL03-0AB0
• CPU 1513-1PN, 300KB Program, 1.5MB Data 6ES7513-1AL02-0AB0
• CPU 1513-1PN, 600KB Program, 2.5MB Data 6ES7513-1AM03-0AB0
• CPU 1515-2PN, 500KB Program, 3MB Data 6ES7515-2AM02-0AB0
• CPU 1515-2PN, 1MB Program, 4.5MB Data 6ES7515-2AN03-0AB0
• CPU 1516-3PN/DP, 1MB Program, 5MB Data 6ES7516-3AN02-0AB0
• CPU 1516-3PN/DP, 2MB Program, 7.5MB Data 6ES7516-3AP03-0AB0
• CPU 1517-3PN/DP, 2MB Program, 8MB Data 6ES7517-3AP00-0AB0
• CPU 1518-4PN/DP, 6MB Program, 60MB Data 6ES7518-4AP00-0AB0
• CPU 1518-4PN/DP MFP + C/C++ RT + OPC UA 6ES7518-4AX00-1AC0

Simatic S7-1500: Failsafe control units (extract)

• CPU 1511F-1PN, 225KB Program, 1MB data 6ES7511-1FK02-0AB0
• CPU 1511F-1PN, 450KB Program, 1.5MB Data 6ES7511-1FL03-0AB0
• CPU 1513F-1PN, 450KB Program, 1.5MB Data 6ES7513-1FL02-0AB0
• CPU 1513F-1PN, 900KB Program, 2.5MB Data 6ES7513-1FM03-0AB0
• CPU 1515F-2PN, 750KB Program, 3MB Data 6ES7515-2FM02-0AB0
• CPU 1515F-2PN, 1.5MB Program, 4.5MB Data 6ES7515-2FN03-0AB0
• CPU 1516F-3PN/DP, 1.5MB Program, 5MB Data 6ES7516-3FN02-0AB0
• CPU 1516F-3PN/DP, 3MB Program, 7.5MB Data 6ES7516-3FP03-0AB0
• CPU 1517F-3PN/DP, 3MB Program, 8MB Data 6ES7517-3FP00-0AB0
• CPU 1518F-4PN/DP, 9MB Program, 60MB Data 6ES7518-4FP00-0AB0
• CPU 1518F-4PN/DP MFP + C/C++ RT +OPC UA 6ES7518-4FX00-1AC0

Simatic S7-1500: SIPLUS (for extreme temperature, vibration, etc.)

• Most of the above modules can also be ordered in SIPLUS version

Simatic S7-1500 Technology: extended technology functions for implementing complex axis synchronizations or kinematic functions (Motion Control)

• CPU 151*T: S7-1500 CPU variants with extended technology functions
• CPU 151*TF: variants with extended technology functions and failsafe

Simatic S7-1500 "Fault-tolerant" and redundant:

• CPU 1513R-1 PN, 600KB program/2.5MB data 6ES7513-1RM03-0AB0
• CPU 1515R-2 PN, 1MB program/ 4.5MB data 6ES7515-2RN03-0AB0
• CPU 1517H-3 PN, 2MB program/8MB data 6ES7517-3HP00-0AB0
• CPU 1518HF-4 PN, 9MB program/60MB data 6ES7518-4JP00-0AB0
• CPU 1513R-1 PN, 300KB program/1.5MB data 6ES7513-1RL00-0AB0
• CPU 1515R-2 PN, 500KB program/ 3MB data 6ES7515-2RM00-0AB0
• SIPLUS S7-1500 CPU 1517H-3 PN 6AG1517-3HP00-4AB0
• SIPLUS S7-1500 CPU 1518HF-4 PN

Software

Programs running on SIMATIC devices run in software environments created by Siemens. The environment varies by product line:

• The SIMATIC S5 product line is programmed in STEP 5.
• The SIMATIC S7 product line is programmed in STEP 7 (V5.x or TIA Portal).^[21]

Step 5

Sample PLC program STEP5 LAD

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

The original STEP 5 versions ran on the CP/M operating system. Later versions ran on MS-DOS, and then versions of Windows through Windows XP. The final version of STEP 5 was version 7.2 (upgradable to version 7.23 Hotfix 1 with patches).

In addition to STEP 5, Siemens offered a proprietary State logic programming package called Graph5. Graph5 is a sequential programming language 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 were released for the S5. Most closely emulated STEP 5, some adding macros and other minor enhancements, others functioning drastically differently from STEP 5. One allowed STEP 5 programs to be cross-compiled to and from the C programming language and BASIC.

Structured programming

STEP 5 allowed 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 (LAD) - Graphical representation of the automation task with symbols of the circuit diagram
• Function Block Diagram (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 keys. They are displayed on the screen as graphical symbols.

There are several program editors, from either genuine Siemens, or from other suppliers. After Siemens discontinued support, other suppliers started to develop new STEP 5 version which can run on Windows XP, or Windows 7.

Blocks

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.

Operations

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) - These can only be executed in STL.

Stuxnet

Main article: Stuxnet

The Stuxnet computer worm specifically targets SIMATIC S7 PLCs via its STEP 7 programming environment.