D

data conversion

During execution, Logix 5000 instructions only operate on DINT and REAL data types. You can specify a SINT or INT tag as an operand and mix data types, but the controller will convert the data before and after instruction execution.

data file

A PLC-5/SLC term.

data set ready (DSR)

A signal that indicates the modem is connected, powered up, and ready for data transmission.

data terminal equipment (DTE)

The equipment attached to a network to send and/or receive data.

data terminal ready (DTR)

A signal that indicates the transmission device (terminal) is connected, powered up, and ready to transmit.

data type

A definition of the size and layout of memory that will be allocated when a tag of the data type is created. Data types can be atomic, structure, or array.

data-carrier detect (DCD)

A signal that indicates the carrier is being received.

data-link escape (DLE)

An ASCII control character used to provide supplementary line communication signals. There are two characters in the sequence: 1.) DLE, and 2.) characters vary according to the function desired and the code used.

dead band

The range of values through which a system input can be varied, upon reversal of direction, without causing a corresponding change in system output.

dead time

The interval of time between initiation of an input change or stimulus and the start of the resulting observable response.

decimal

Pertains to the base-10 numbering system.

delete zone (D rung)

An edit zone that indicates a rung that has been deleted while in Run mode. The rung is only executed in Untest Edits mode and cannot be edited.

delimiter

A character that separates items of data. When placed before and/or after a string of data, a delimiter causes the data to be interpreted in a predetermined manner.

derivative control

See proportional, integral, derivative control (PID).

derivative time

The time over which a derivative between the current value and the previous value is calculated.

description

A representation that can be a maximum of 128 bytes in length. You can use any printable character; carriage returns, tabs, and spaces are also supported. Standard ASCII characters consume 1 byte per character, allowing for 128 characters. Note that some characters (for instance, those used for Asian languages) take up to three bytes to represent one character, resulting in less than 128 characters maximum.

destructive

A reference that sets the value of a tag.

DeviceNet network

A global industry-standard open communication network. It is designed to provide an interface through a single cable from a programmable controller processor directly to "smart" devices such as sensors, push buttons, motor starters, simple operator interfaces, and drives.

DF1 protocol

A peer-to-peer link-layer protocol that combines features of ANSI X3.28-1976 specification subcategories D1 (data transparency) and F1 (two-way, simultaneous transmission with embedded responses).

DH link

Data Highway link. An Allen-Bradley floating-master baseband link for a local area network.

DH-485 link

Data Highway 485 link. An Allen-Bradley token-passing baseband link for a local area network based on the RS-485 standard.

DH+ link

Data Highway Plus link. An Allen-Bradley token-passing baseband link for a local area network.

dialog box

A box that appears on the screen displaying available options for the selected menu item. Dialog boxes may contain components such as editable text fields, check boxes, list boxes, action buttons, and radio buttons.

Differential mode

An operating mode used by analog input modules where each input channel uses two wires connected to two hardware channels. The instrument measures the signal difference between the two wires.

dimension

The specification of the size of an array. An array has one or more dimensions.

DINT

An atomic data type consisting of a DWORD used to store a 32-bit signed integer value (-2,147,483,648 to +2,147,483,647).

direct command

A motion command that is sent directly to the controller from the software as a result of a user action. These commands execute without being initiated by a user program.

direct data

In the context of the SynchLink protocol, direct data is data that is passed every 50 ms. With a properly configured daisy chain topology, direct data can be passed to and seen by up to 10 nodes in 500 ms.

direct I/O module

An I/O module where each input/output has an individual circuit connection, directly corresponding, to a data table bit or word. The bit or word stores the value of the signal at the I/O circuit (digital or analog). This allows the ladder logic to have direct access to the I/O values.

directory

A storage area on your hard drive. A directory is also referred to as a folder.

Disable Keying

Disable Keying indicates that the keying attributes are not considered when attempting to communicate with a device. With Disable Keying, communication can occur with a device other than the type specified in the project.

disqualified secondary

A control chassis that may have had, or currently has, a partner primary control chassis, but is now incapable of performing a control function if the primary chassis fails.

divergence and convergence

When you create an alternate (selective) or parallel (simultaneous) path for the execution of steps in your Equipment Sequence diagram by adding a simultaneous or selective branch, you create a divergence. You merge branch paths back into one path using a convergence branch.

domain

A logical grouping of clocks that synchronize to each other using the PTP protocol, but they are not necessarily synchronized to clocks in another domain.

domain name

The domain name can have the following format:

where a, b, c, and d may contain only letters, digits, and hyphens. The total number of characters, including the ".", must be 48 or less. If you enter an invalid name, the software will not accept it and will display an error message.

The portions of a domain name may be all numeric, except for the last portion. For example, you may have the following:

but NOT:

download

The process of transferring the contents of a project file on the workstation into the controller or other device.

drift

A term used to describe the cumulative offsets of the servo module’s DAC output, and the servo drive input, resulting in a situation where a zero commanded servo output value causes the axis to move (or "drift".) A common condition when interfacing an external servo drive, particularly for velocity servo drives, due to the effect of drives offset. If the drift is excessive, it can play havoc on the hookup diagnostic and tuning procedures, as well as result in a steady state, non-zero position error when the servo loop is closed.

drive

An electronic device that can control the speed, torque, horsepower, and direction of an AC or DC motor.

drive fault

An undesirable condition that occurs on the drive associated with a given axis causing it to go to a fault state.

Drive Peripheral Interface (DPI)

A non-CIP port that allows the connection of one of several DPI device types.

Two DPI ports exist in the PowerFlex 700S drive. One of these is generally used locally by a handheld terminal. The second is generally used with a port extender that expands one port into four, thereby providing four free ports. These ports can then be used for one or more communication interface cards for ControlNet, DeviceNet, EtherNet, etc, allowing network access to the drive. This is especially useful when no DriveLogix 5720 controller is present.

The second port can also be used by an Anaconda, which is a device allowing a standalone computer to connect to the drive via a serial connection.

Messages and connections cannot bridge between a DPI port and the CIP virtual backplane.

drive type - torque

A drive that requires a torque command and does not have an active internal velocity loop. The local servo module’s internal digital velocity loop is active.

drive type - velocity

A drive that requires a velocity command because it has an active internal velocity loop. The local servo module’s internal digital velocity loop is not active.

driver

A source output for hardware. When turned on, it supplies a positive DC current to its load.

OR

A software subroutine that handles the logic for communicating with a specific type of external device.

dual control chassis redundancy

A method of redundant control that specifies the use of two control chassis: a primary control chassis and a secondary control chassis. The primary control chassis performs all control functions. If this chassis fails, control transfers to the secondary control chassis.

dual redundancy

A form of redundancy involving a pair of devices that operate with one device performing the assigned functions while the other remains in some state of secondary readiness (that is, the ability to assume responsibility for the assigned functions in the event that the first device experiences a failure).

duplicate I/O addressing

A method of expanding the number of I/O by assigning the same location address to 2 different I/O modules.

duration

The time during which something exists or lasts (for example, the length of time that a signal is high may be described as the duration of a pulse).

duty cycle

The ratio of working time to total time for an intermittently operating device (usually expressed as a percentage).

DWORD

Double Word. A storage location in memory consisting of a group of 32 bits (or 4 bytes, or 2 words).

Dynamic Data Exchange (DDE)

A form of inter-process communication. When two or more programs that support DDE are running simultaneously, they can exchange information and commands.

Dynamic Host Configuration Protocol (DHCP)

An Internet protocol for automating the configuration of computers that use TCP/IP. You can use DHCP to automatically assign IP addresses, to deliver TCP/IP stack configuration parameters (for example, subnet mask and default router), and to provide other configuration information, such as the addresses for printer, time, and news servers.