Instruction Manual

Rockwell Automation Publication 1769-UM006E-EN-P - July 2013 159
Glossary
coordinated system time (CST) Timer value which is kept synchronized for all modules within a single
ControlBus chassis. The CST is a 64-bit number with s resolution.
data 1) A general term for any type of information. 2) In a more restricted sense, data
refers to the end-use information in the particular context; thereby excluding the
protocol information used to get the end-use information.
data table The part of processor memory that contains I/O values and files where data is
monitored, manipulated, and changed for control purposes.
database The entire body of data that has to do with one or more related subjects.
Typically, it consists of a collection of data files.
differential 1) Pertaining to a method of signal transmission through two wires. The
transmission always has opposite states. The signal data is the polarity difference
between the wires; when one is high, the other is low. Neither wire is grounded.
The circuit can be either a balanced circuit, a floating circuit, or a circuit with a
high-impedance path to ground from either end. Usually used in reference to
encoders, analog I/O circuits, and communication circuits. 2) Contrasted with
single-ended (
page 163).
digital circuit 1) A switching circuit that has only two states: on and off. 2) A circuit that
provides a step function. 3) Contrasted with analog circuit (
page 157).
direct connection An I/O connection where the controller establishes an individual connection
with I/O modules.
direct I/O module 1) An I/O module for which each input or output that has an individual
connection that corresponds directly to a data table bit or word that stores the
value of the signal at that I/O circuit (digital or analog). This lets the ladder logic
have direct access to the I/O values. 2) Contrasted with intelligent I/O module
(
page 161).
disable keying Option that turns off all electronic keying to the module. Requires no attributes
of the physical module and the module configured in the software to match.
download The process of transferring the contents of a project on the workstation into the
controller.
duration 1) The time during which something exists or lasts. For example, the length of
time that a signal is high can be described as the duration of a pulse. 2) Compare
interval (
page 161) and period (page 162).