| alphanumeric |
Consisting of or using both letters and numerals. |
| bit memory |
M. A type of PLC memory that contains the possible bit locations in a PLC's CPU. Bit memory, along with the input and output bits of the process image, make up the global memory of a PLC. |
| Boolean logic |
A type of logic that deals with the use of logical functions such as OR, AND, and NOT. |
| code block |
A program block in a PLC program. A Siemens PLC can have three types of program blocks: organization blocks (OBs), function blocks (FBs), and functions (FCs). |
| consecutive binary bits |
Binary bits that fall one after another that may be used individually or as a group. |
| constant |
A value or number that does not change. |
| data block |
DB. An organized set of data in a Siemens PLC program that is used by one or more program blocks. An instance DB stores data use by one program block. A global data block contains data that is available to any program block. |
| data type |
A description of the data in a PLC that indicates the pattern the PLC should read the bits in. Different data types use bit groups of different sizes. |
| DB |
Data block. An organized set of data in a Siemens PLC program that is used by one or more program blocks. An instance DB stores data use by one program block. A global data block contains data that is available to any program block. |
| DWord |
Double word. 32 consecutive binary bits. |
| electronic drives |
Devices used to control the speed of electric motors. |
| engineering software |
Software used to design, operate, and maintain a control system. STEP 7 Basic and STEP 7 Professional are examples of engineering software used with Siemens PLCs. |
| FB |
Function Block. A type of program block used in a Siemens PLC program. A function block requires an assigned data block. |
| FBD |
Function block diagram. A graphical PLC programming language defined in part 3 of the IEC 61131 standard. |
| FC |
Function. A type of program block used in a Siemens PLC program. An FC has no assigned data block. |
| function |
FC. A type of program block used in a Siemens PLC program. An FC has no assigned data block. |
| function block |
FB. A type of program block used in a Siemens PLC program. A function block requires an associated data block.” |
| function block diagram |
FBD. A graphical PLC programming language defined in part 3 of the IEC 61131 standard. |
| global data block |
Global DB. A type of data block which contains data that is available for use by any code block. |
| global DB |
Global data block. A type of data block which contains data that is available for use by any code block. |
| global memory |
A type of PLC memory that is available to all code blocks. Global memory includes both the input and output bits of the process image and the bit memory. |
| HMI |
Human Machine Interface. A device or system that displays machine or process information and allows values to be changed. |
| IEC 61131 |
The International Electrotechnical Commission standard for PLCs. Part three of this standard, IEC 61131-3, defines PLC programming languages. |
| IL |
Instruction list. A low-level, text-based programming language. Instruction list uses compact code to optimize memory usage and for Siemens PLCs is referred to as statement list or STL. |
| industrial personal computer |
Personal computers designed for use in industrial environments. They are used for information technology and control purposes. |
| instance data block |
Instance DB. A data block used to store data for a specific function block. |
| instance DB |
Instance data block. A data block used to store data for a specific function block. |
| instruction list |
IL. A low-level, text-based programming language. Instruction list uses compact code to optimize memory usage and for Siemens PLCs is referred to as statement list or STL. |
| Int |
Signed integer. A data type for 16-bit signed whole numbers. |
| interrupt |
A special signal or condition that causes a PLC to immediately perform a specific task. |
| LAD |
Ladder diagram. A graphical programming language that is defined in IEC 61131-3 and derived from the diagrams used in electromechanical control circuits, though it has expanded to include more advanced capabilities. Ladder diagram programming is also known as ladder logic. |
| ladder diagram |
LAD. A graphical programming language that is defined in IEC 61131-3 and derived from the diagrams used in electromechanical control circuits, though it has expanded to include more advanced capabilities. Ladder diagram programming is also known as ladder logic. |
| linear program |
A PLC program whose instructions are contained in one main program block, called organization block 1, or OB1. Linear programs are executed with each PLC scan. |
| load memory |
Non-volatile storage for the user program, program data, and configuration information. When a project is first loaded into the CPU, it is stored in the load memory. |
| M |
Bit memory. A type of PLC memory that contains the possible bit locations in a PLC's CPU. Bit memory, along with the input and output bits of the process image, make up the global memory of a PLC. |
| memory address |
A location for memory stored within a PLC. Memory addresses may be used as operands. |
| modular program |
A type of program that consists of multiple program blocks, some of which may be executed during each PLC scan while others are only executed under special circumstances. Compared to linear programs, modular programs are easier to understand, develop, and debug. |
| nested |
The ability of a program block to be called by another program block. Mulitple programs can be nested inside of each other in a modular program. |
| non-volatile |
Indicates that a type of memory retains its data even in the event of a power loss. |
| OB |
Organization block. A type of data block used to define the structure of a PLC program. Every PLC program must have at least one OB. |
| operand |
An identifier associated with a PLC instruction that specifies a value or memory location used by that instruction. |
| operating system |
The software on a computer that allows files to be created and organized, manages the interaction of different programs, holds data in memory, and performs other functions. |
| organization block |
OB. A type of data block used to define the structure of a PLC program. Every PLC program must have at least one OB. |
| PC |
Personal computer. PCs with engineering software can be used for PLC programming. |
| personal computer |
PC. PCs with engineering software can be used for PLC programming. |
| PLC |
Programmable logic controller. An industrial computer used to control machines and processes. |
| retentive memory |
Non-volatile storage for a limited quantity of work memory values. Retentive memory is used to store the values of selected user memory locations during power loss. |
| RUN |
The operating mode in which the CPU executes the PLC scan repeatedly. |
| S7 – Graph |
A type of engineering software included in the SIMATIC STEP 7 Professional package. S7-Graph is a graphical programming language that shows steps in a sequence, making it easy to see the order in which events will occur. |
| S7 – PLCSIM |
A type of engineering software included in the SIMATIC STEP 7 Professional package which enables the functional testing of PLC programs on the programming device without a PLC attached. |
| S7 – SCL |
A type of engineering software included in the STEP 7 Basic and STEP 7 Professional that allows development of structured control language programs. |
| scan |
One complete cycle of a PLC’s cyclical operation that includes checking inputs, executing its programs, updating the status of its outputs, and performing various other required processes. |
| SCL |
Structured control language. A high level programming language, also known as structured text. |
| sequential function chart |
SFC. A graphical programming language included in STEP 7 Professional as S7-Graph. |
| SFC |
Sequential Function Chart. A graphical programming language included in STEP 7 Professional as S7-Graph. |
| signed integer |
Int. A data type for 16-bit signed whole numbers. |
| SInt |
Signed short integer. A data type for 8-bit signed whole numbers. |
| statement list |
STL. A low-level, text-based programming language that uses compact code to optimize memory usage. Statement list is also known as instruction list. |
| STEP 7 Basic (TIA Portal) |
PLC engineering software used for the configuration and programming of S7-1200 PLCs and related devices. |
| STEP 7 Professional (TIA Portal) |
PLC engineering software used for the configuration and programming of most Siemens S7 PLCs and related devices. |
| STL |
Statement list. A low-level, text-based programming language that uses compact code to optimize memory usage. Statement list is also known as instruction list. |
| structured control language |
SCL. A high level programming language, also known as structured text. SCL is suitable for high-speed programming of complex algorithms and arithmetic functions. |
| structured text |
A high level programming language, also known as structured control language or SCL. SCL is suitable for high-speed programming of complex algorithms and arithmetic functions. |
| subroutine |
Portions of a program that are executed once a specific condition in the program has been met. |
| tag |
A symbolic identifier used in engineering software to associate an instruction or item with a memory area. |
| tag table |
An area of a PLC's CPU where the various tags are stored. |
| TIA Portal |
Totally integrated Automation Portal. Engineering software used for design, operation, and maintenance of Siemens automation systems, including many Siemens PLCs. |
| Totally Integrated Automation Portal |
TIA Portal. Engineering software used for design, operation, and maintenance of Siemens automation systems, including many Siemens PLCs. |
| volatile |
Indicates that a type of memory loses its stored data in the event of a power loss. |
| work memory |
Volatile storage for some elements of a user's project that are used while the project is getting executed. |