A - C

access control

The use of password-protection to control access to projects, controllers, programs, libraries, and targets.

accuracy

The degree to which the result of a measurement conforms to the correct value.

action

A collection of operations to perform whose execution differs for each programming language.

actuator

A device, like a valve or pump, causing an electrical, mechanical, or pneumatic action to occur in a plant component.

add-in

A plug-in, utility, driver, or other software added to a primary application that extends its capabilities.

address

A unique identifier used to locate a resource, such as the optional hexadecimal address that can be defined for each variable or controller. Addresses can be used by external applications to access values of variables on a resource.

alias

The property of a variable indicating a short name for the variable. For graphical programs, aliases indicate the parameters in functions and function blocks.

arbitration

A mechanism for deciding which controller, device, module, or peer has control.

architecture

Organizational structure of a computing system describing the functional relationship between the board level, device level, and system level components.

array

Set of elements of the same type referenced by one or more indexes enclosed in square brackets and separated by commas. The index is an integer. Examples: tabi[2] or tabij[2,4].

asynchronous

Data communications term describing a serial transmission protocol. A start signal is sent before each byte or character and a stop signal is sent after each byte or character.

attribute

The property of a variable indicating whether a variable is read-only, write-only, or read and write.

battery alarm

Alarm signal indicating back-up battery voltage is low or not present.

battery backup

Internal battery powering the internal Real Time Clock (RTC) and a portion of the volatile memory (RAM) when the power is off.

binding

Bindings are links, for example access paths, between variables located in different controllers. From a controller, bindings are defined as having a producer variable sending values to a consumer variable. The system updates the values in the consumer to match the values in the producer.

Boo action

A Boolean variable where the value corresponds to Step activity (0=inactive and 1=active). Possible qualifiers are Action (N), Reset (R), and Set (S).

boolean (BOOL)

Basic type that can be used to define a variable, a parameter or an I/O module. A boolean can be TRUE (1) or FALSE (0).

breakpoint

A mark placed by the user at particular locations within the code. While simulating, the application stops when it encounters a breakpoint. Breakpoint implementation varies for each programming language.

build configuration

A way to store multiple versions of project properties. Build configurations are modifiable. Note that configuration is in the sense of settings.

byte

Unsigned integer 8-bit format. Basic type that can be used to define a variable, a parameter, or an I/O module.

C Function

A function written using the "C" language, that can be called from program organization units in a synchronous manner.

C Language

Programming language used to access particularities of the target system. C language can be used to program C functions, function blocks, and conversion functions.

call stack

A data structure of information about the routines in a program that can be used to track the steps between program organization units and called functions. Some debug information includes call stacks to assist in troubleshooting.

cell

An individual area of a graphic matrix. Used with graphic languages and displays.

channel

A hardware input/output point that can be connected to a controller. A channel is either an input or output. To enable use in program organization units, variables including directly represented variables are connected to channels.

check in

Sending the contents of elements including projects, I/O modules, controllers, and program organization units for storage in a version control database. Checked-in elements can be recovered at a later time.

child

A subordinate program which is activated by its parent. The child program has only one parent. Only the parent can start or stop child program. A parent can have more than one child.

Common Industrial Protocol (CIP)

A communications protocol for use with automation system controllers which sends data to and from controllers using a consume/producer model.

coil

A graphic component representing the assignment of an output or an internal variable. Standard defined in IEC 61131-3.

common scope

Scope of a declaration applying to all program organization units within a project. (Only defined words and types can have common scope).

condition

A boolean expression attached to an SFC Transition. In case of an SFC transition, the transition cannot be cleared when its condition is false.

configuration

A grouping of the application and settings specified for a controller.

connection

The link between different system components, such as networks and controllers.

constant expression

Literal expression used to describe a constant value.

consumer

The controller requesting the tag data from another controller.

consumer group

A group holding external producer variables with bindings with consumer variables defined in the project.

consumer status variable

Variables that enable the management of binding errors at the consumer level.

consumption error behavior

Indication of the value to use when an error occurs for an internal binding. Possible values are either the last value issued from the binding or a specified default value.

contact

Depending on the type of contact, a graphic component representing the value or function of an input or an internal variable.

continuous mode

Where the Safety Instrumented Function in the safety system continually maintains the process in a safe condition.

controller

A programmable logic controller made up of one or more programs.

controller system

One or more controllers, along with their power sources, communication networks, and workstations.

controller variable

A variable whose scope is global to the project.

conversion

Filter attached to an input or output variable. The conversion is automatically applied each time the input variable is read or the output variable is refreshed.

conversion function

A function written in the "C" language that describes a conversion process. The conversion can be attached to any input or output, integer or real variable.

coverage

The percentage of faults detected by automated diagnostics.

Comma Separated Values (CSV) file format

A delimited data format with each piece of information separated by commas and each line ending with a carriage return. The CSV file format can be used for importing or exporting variables data.

cycle

The order of execution for the programs of a controller. All programs of the controller are executed following the order defined by the user, from the first program to the last and again and again. Before the execution of the first program, inputs are read. After the execution of the last program, the outputs are refreshed.

cycle timing

The amount of time given to each cycle. If a cycle is completed within the cycle timing period, the system waits until this period has elapsed before starting a new cycle. The cycle consists of scanning the physical inputs of the process to drive, executing the program organization units of the controller, then updating physical outputs. The cycle time can differ for each cycle when no cycle timing is specified. When the cycle timing is shorter, the virtual machine waits until this time has elapsed. When the cycle time is longer, the virtual machine immediately scans the inputs but signals with the "overflow" that the programmed time has been exceeded. When the trigger cycles property is false or the cycle time is 0, the virtual machine does not wait to start a new cycle.

cycle-to-cycle mode

Execution mode of a controller where cycles are executed one by one, according to the orders given by the user during debugging. Another execution mode for controllers is real-time mode.

cyclic program

A time independent program that is executed during each cycle.