Glossary
Appendix D
D-10
Hardware
The mechanical, electrical, and electronic devices which compose a
programmable controller and its application
Header Rung
The first level of a ladder diagram program. It is a requirement when
programming PLC-2 family processors or on the Data Highway.
Hexadecimal Numbering System
A base-16 numbering system that uses the symbols 0, 1, 2, 3, 4, 5, 6, 7, 8,
9, and A, B, C, D, E, F.
High=True
A signal type where the higher of two voltages indicates a logic state of
On (1). See Low=True.
Image Table
An area in processor memory dedicated to I/O data. Ones and zeros (1 and
0) represent On and Off conditions, respectively. During every I/O scan,
each discrete input controls a bit in the input image table; each discrete
output is controlled by a bit in the output image table.
Information
The meaning assigned to data by known conventions.
Input Devices
Devices such as limit switches, pressure switches, pushbuttons, analog
devices, and/or digital devices, that supply data to a processor.
Instruction
A command that causes a processor to perform one specific operation. The
user enters a combination of instructions into processor memory to form a
unique application program.
Integer
Any positive or negative whole number or zero.
Intelligent I/O Module
Microprocessor-based modules that perform processing or sophisticated
closed-loop, application functions.
Interference
Any undesired electrical signal induced into a conductor by electrostatic or
electromagnetic means.
H
I
