STEP 7

STEP 7 blocks

STEP 7 files all user programs and all the data required by those programs in blocks. The possibility of calling other blocks within one block, as though they were subroutines, enables the structuring of the user program. This makes the PLC programs much more clearer and easier to understand and update. The following types of block are available:

• Data handling blocks (DHBs) control program execution.
  • OBs are divided into classes (e.g., time-driven, alarm-driven) based on the triggering event. Depending on their respective priority levels, one can interrupt another.
  • When an OB is started, detailed start information about the triggering event is provided. This information can be evaluated in the user-written program.
• Function blocks (FBs) contain the actual user program.
  • Function blocks can be supplied with different data each time they are called (the so-called instance). These data, as well as internal variables (e.g., for intermediate values) and results are stored in the assigned instance data block and are automatically managed by the system.
• When an FB/SFB is called, instance data blocks (instance DBs) are assigned to the block. They are automatically generated when these blocks are compiled.
  • The user can access these instance data (symbolically as well, of course) from any point in his user program or from an HMI system.
• Functions (FCs) contain program routines for frequently used functions.
  • Every function has a fixed function value (a number of initial parameters are possible, in addition to the IEC standard). The output parameters must be processed immediately after the call. Thus functions do not require any instance-data blocks.
• Data blocks (DBs) are data areas for storing user data.
  • In addition to the data that is assigned in each case to a function block (instance data), global data can be defined and can be used by any of the software modules (e.g., for recipes).
  • An elementary or structured data type can be assigned to the components of a data block. Elementary data types are, for example, BOOL, REAL or INTEGER. Structured data types (fields and structures) comprise elementary data types (e.g., a recipe). The data in a data block can be addressed symbolically. This facilitates the programming and the readability of the program.
• System function blocks (SFBs); function blocks (see above) that are integrated in the CPU's operating system, e.g., SEND, RECEIVE, controller. The variables of the SFBs are also filed in IDBs.
• System functions (SFCs); functions (see above) that are integrated in the CPU's operating system, e.g., time functions, block transfer.
• System data blocks (SDBs) are data for the CPU's operating system containing the system settings, e.g., module parameters.

Tools

SIMATIC Manager

The SIMATIC Manager manages all data belonging to an automation project, regardless of the target system (SIMATIC S7, SIMATIC C7 or SIMATIC WinAC) on which they are implemented.

It provides a common entry point for all SIMATIC S7, C7 or WinAC tools. The SIMATIC software tools that are necessary for processing the selected data are automatically started by SIMATIC Manager.

Symbol editor

The symbol editor tool is used to manage all the global variables (in contrast to the local formal parameters that are declared when the block is programmed). The following functions are available:

• Definition of symbolic designations and comments for the process signals (inputs/outputs), flags and blocks
• Sorting functions
• Data exchange with other Windows programs

The symbol charts that are generated when this tool is used are available to all applications. Changes to a symbol parameter are therefore automatically detected by all tools.

Hardware configuration

The hardware configuration tool is used for configuring and parameterizing the hardware of an automation project. The following functions are available:

• Configuration of the automation system:
  Racks are selected from an electronic catalog and the selected modules are assigned to the required slots in the racks.
• The configuration of the distributed I/Os is done in the same way as the configuration of the non-distributed I/Os; channel-granular I/O modules are also supported.
• CPU parameter assignment:
  Properties such as restart characteristics and cycle-time monitoring can be set menu-driven. Multicomputing is supported. The entered data are filed in system data blocks in the CPU.
• Module parameter assignment:
  The user can specify all the adjustable parameters of the modules in input screen forms. Adjustments via DIP switches become unnecessary. The modules are parameterized automatically when the CPU starts up. Thus, an exchange of a module can be made without another parameterization.
• Function module (FM) and communication processor (CP) parameter assignment:
  This parameterization also occurs within the hardware configuration in the same way as the parameterization of the other modules. For this parameterization hardware-module-specific screen forms and rules are provided for each FM and CP (is included in the FM/CP functions package). The system prevents faulty inputs by offering only allowed entry options on the parameter assignment screen forms.

System diagnostics

System diagnostics provides the user with an overview of the status of the programmable controller. There are two display modes:

• Display of text messages, which can be output directly and quickly
• Pixel-graphics display within the Hardware Config display, offering the following options:
  • Display of general module information (e.g., Order No., version, designation) and module status (e.g., faulty)
  • Display of module faults (e.g., channel faults) of the central I/O and DP slaves
  • Display of alarms from the diagnostics buffer

For CPUs, additional information is displayed:

• Causes of malfunction during user program execution
• Display of cycle duration (longest, shortest and last cycle)
• Display of the reserved and free memory
• Capabilities and usage of MPI communication
• Display of the performance data (number of possible inputs/outputs, flags, counters, timers and blocks)

Communication configuration

• Configuring and display of communication links
• Time-driven cyclic data transmission via MPI
  • Selection of communication partners
  • Entering of data source and data destination in a table. generation of all system data blocks (SDBs) to be loaded and their complete transmission to all CPUs take place automatically.
• Event-driven data transmission:
  • Definition of the communication links
  • Selection of the communication function blocks (CFBs) from the integrated block library
  • Parameterization of the selected communication blocks in the customary programming language (e.g., LAD)

Programming languages

The well-proven programming languages Ladder (LAD), Function Block Diagram (FBD) and Instruction List (IL) are available for programming. Programs that comply with DIN EN 6.1131-3 can be created in the classical PLC programming languages Ladder (LAD) and Function Block Diagram (FBD) .

The user-friendly, pixel-graphics LAD and FBD editors support the programmer with:

• Uncomplicated and intuitive operation:
  The creation of ladder diagrams/function block diagrams is characterized by the user-friendliness familiar from PCs, such as drag and drop, cut and paste.
• Library of predefined complex functions (such as PID controllers) or user-specific standard solutions

The Instruction List (IL) textual programming language makes it possible for the user to create programs in which operating time and memory location are optimized and which are “close to the hardware”. When creating these programs, the programmer is supported by the following user-friendly editing functions:

• Entry option in incremental mode and free text mode:
  the user can either have each input immediately checked “incrementally” for correctness, or create the complete program using only symbols in a text editor and subsequently have it translated by means of the appropriate symbol chart.

Operation set

The STEP 7 programming languages have a comprehensive set of instructions, similar to STEP 5. This allows even complex functions to be programmed easily (i.e., without having great programming knowledge) and quickly

The following functions are provided:

• Binary logic (incl. edge evaluation)
• Word operation
• Timers/counters
• Comparison functions
• Conversion functions
• Shift/rotate
• Mathematical functions (incl. trigonometry, exponents, logarithms)
• Program control (jumps, jump list, calls, master control relays)

In addition, improved testing and service functions make programming easier:

• Setting breakpoints (only S7-400)
• Forcing of inputs/outputs (only S7-400)
• Rewiring
• Display of cross-references

STEP 7 supports multicomputing with the S7-400.

Status functions:

• Download and testing of blocks directly from the editor
• Status of several blocks at the same time
• Search functions:
  Specific locations within the program can be found quickly using search criteria (such as symbolic name, operand) (XRef).

Online Help is available for all functions and blocks (F1).

Note:
Screenshot views are available for the individual STEP 7 tools.

S7-SCL

• Integrated user interface with editor, compiler and debugger
• Symbolic linking in the debugger
• Language elements known from high-level language programming, such as serial loops, alternative branching and branch distributors
• Language extensions typical for PLCs, such as addressing of inputs and outputs or start and querying of timers and counters
• Elementary and self-defined data types for clearly structured PLC programs Symbols and comments further enhance understanding
• Source concept that supports symbols-only programming and storage of the entire program in a source file
• Generation of optimized code with low compilation effort
• Display of cross-references
• High-level language test of user programs is possible (as known from other PLC languages)
• Link to project-wide documentation system (DOCPRO)

S7-GRAPH

• Overview diagram:
  The complete sequential structure can be displayed.
• Single-page display:
  The sequential structure, the step enabling conditions and the step actions can be displayed together on a single page.
• Detail display:
  The actions, transitions (with the step enabling conditions) and interlocking and monitoring conditions associated with a step are displayed together.
• Flexible configuration of step sequences:
  With simultaneous and alternative branches, jumps within the sequence chains, step activation and deactivation, the user has a number of options for describing his task. In the same block, any number of parallel asynchronous step sequences can be configured.
• Scope of language:
  The scope of the language facilitates user programming of conditions and actions.
• Online functions:
  Display of active steps, status of Interlocking, monitoring and step enabling conditions, in addition to the actions executed.
• Performance:
  Good performance is achieved by selective processing of the steps. The processing time of a sequence of steps is independent of the number of steps.
• Link to a project-wide documentation system (DOCPRO)
• Memory requirements of the administration section can be adjusted as necessary;
  S7-GRAPH provides different settable compiler options for integrating the general management section of the sequencer block:
  • Option "can execute autonomously":
    The management section (approx. 5 KB) is included in every function block generated by S7-GRAPH. This is the solution for small applications with only one sequencer block.
  • Option with "standard FC”:
    The management section is swapped to a separate block that exists only once per project and is shared by all sequencer blocks. Depending on the type of this standard FC, the memory requirement can be 8 or 10 KB.
• System function "FC 73" (V5.1 or newer):
  The FC 73 supports reduced-memory solution of under 8 KB, which is especially interesting in smaller CPUs of the S7-300. The following restrictions are valid when using the FC 73:
  • The blocks created have no diagnostics capability.
  • The visualization of the blocks created is limited.
• Synchronization functionality:
  Operation sequences can be controlled and synchronized with the current state of the system/machine. In the event of program changes involving the download of the instance data block, the sequence is automatically reset to its initial state. The "Control sequence" function supports the setting and resetting of steps directly from the PG, so that the sequence can be reset to the system status prior to the program change. Synchronization operations can also be performed directly from the PG. This will automatically cover all transitions and interlock conditions, and the respective steps will be flagged. The user can then simply select and activate the step(s).
• User-defined call interface:
  There are two possibilities for the call interface of the sequencer block:
  • Predefined parameter sets, optionally Mini, Standard and Maximum
  • User-defined parameters for flexible adaptation to the needs of the application
• Comprehensive diagnostic functions:
  Causes of malfunctions are found by indicating or reporting the faulty step. Moreover, incorporation into the SIMATIC diagnostics concept with SIMATIC ProTool/Pro and SIMATIC ProAgent supports the simple integration of operator panels and WinCC to display faults in plain text and show the cause signals (criteria analysis).
• Expandable printer functions (V5.1 or newer):
  • A page break always follows a "sequence step plus transition".
  • A page break is adjustable at the end of the sequencer/graph.
  • A specific comment can be entered for each graph.
• Improvement of the window structure (V5.1 or newer):
  The S7-GRAPH project window contains only the sequencer to be edited. All additional information that are needed for programming upon request can be revealed or hidden through the following windows:
  • Information on the interface of the block (block parameter and variables)
  • Addresses used (including status display for all data types)
  • Cross-references to other locations of the addresses in the program
  • Symbols used from the symbol table
• Simultaneous selection of several objects with usual Windows procedures (V5.1 or newer):
  • Lasso function (selection frame around the desired elements) with "cut, copy, paste" for simple and quick copying and deletion of sequence steps and transitions.
  • Elements that are not adjacent can be selected via the "Ctrl" key.
  • With parallel structures, individual branches or graphs can be selected with the lasso function and deleted.

Mode of operation

Sequence chains display the individual steps of a process and the transitions to the next steps as rectangles and lines (illustration). Within the steps, actions can be initiated by so-called "qualifiers" (e.g., time-delayed or conditional execution). If, for example, the operating sequence describes a drilling process, the "lowering of the drill" will be a step and the "activation of the motor" will be an action.

The transitions describe the conditions under which a transition to the next step should occur. In the example of the "drilling process", the criterion for step-enabling the operation sequence would be fulfilled if the condition "lower final position reached" is met.

In addition, interlocking and monitoring conditions can be defined for every step.
An interlock can be used to prevent the execution of actions. Monitoring conditions enable the recognition of operational faults. All conditions (transitions, interlocking or monitoring) can be programmed either in LAD or CSF.

S7-PLCSIM

S7-PLCSIM is totally integrated in STEP 7. This means that the following additional functions are available:

• STEP 7 test and startup functions
• Test functions of the programming languages used (see S7-PLCSIM application)

During the tests, a range of convenient functions are available with S7-PLCSIM to support the user:

• Choice of modes:
  • Continuous
  • 1 cycle
• Display of accumulators, block registers and nesting stacks
• User interface for monitoring and modifying inputs, outputs, memory bits, timers, counters, and data
• Trigger error OBs

Mode of operation

S7-PLCSIM simulates a SIMATIC S7 CPU with the associated process images. Similarly to the procedure with real hardware, the program under test is loaded into the simulated S7 CPU for subsequent execution. S7-PLCSIM also supports an interface that permits the exchange of process values between S7-PLCSIM and other Windows applications. Communication is based on ActiveX-Control, e.g., for interfaces:

• Reading/writing of process values
• Modifying execution mode (e.g., 1 cycle)