STEP 7 LITE blocks

In the case of STEP 7 LITE, all the user programs as well as the data that they use are stored in blocks. The possibility of calling other blocks within one block, as though they were subroutines, enables the structuring of the user program. This increases considerably the organizational clarity, the comprehensibility and the ease of maintenance of PLC programs. The following types of blocks are available:

• Data handling blocks (DHBs) control program execution.
  • OBs are divided into classes (e.g., time-driven, alarm-driven), independently of the triggering event. These classes have levels of priority. Depending on their respective priority levels, one can interrupt another.
  • When an OB is started, detailed information about the event initiating the start 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.
  • Each function has a fixed function value (as an expansion to the IEC standard, several output parameters are possible). 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) are built up from elementary data types (e.g., a recipe). The data of a dat block can be symbolically addressed. 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

Project overview

The project overview manages all the data belonging to an automation project – regardless of the target system (SIMATIC S7, SIMATIC C7 or ET 200S/X) on which they are located.

Symbol Editor

With the tool Symbol Editor all global variables (in contrast to the local formal parameters that are declared when the blocks are programmed) are managed. 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 recognized by all tools.

Hardware configuration

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

• Configuration of the automation system
  The selected modules are assigned to the required slots in the racks.
• CPU parameter assignment:
  Properties such as restart characteristics and cycle-time monitoring can be set menu-driven. 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. Parameterization of hardware modules occurs automatically during the CPU's acceleration. Thus, a change of a module can be made without another parameterization.

System diagnostics

System diagnostics offer the user an overview of the status of the automation system. The display can be in two different forms:

• 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 number, version, designation) and module status (e.g., faulty)
  • Display of faults in central I/O modules
  • 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
• Display of the performance data (number of possible inputs/outputs, flags, counters, timers and blocks)

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 ready-to-use complex functions (e.g., PID controls)

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 check every input immediately for correctness "incrementally" or create the complete program in any text editor symbolically and then compile it using the correct symbol table.

Operation set

The programming languages of STEP 7 LITE feature a comprehensive instruction set. 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 (branches, branch distribution, calls, Master Control Relays).

Test functions and supply functions also make programming easier:

• Set breakpoints (provided that this is supported by the CPU)
• Forcing of inputs and outputs (provided that this is supported by the CPU)
• Rewiring
• Display of cross-references.

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).