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Glossary
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A method in which one element in a system monitors changes in the con-
tents of certain data words to maintain accurate records of the contents. In a
PC Link System, polling is performed by the polling unit to maintain common
data areas among PCs.
The PC Link Unit in a PC Link System that handles data transmissions to
maintain common data areas within the PCs. In a PC Link System, the poll-
ing unit always shares common data areas with the polled units.
A board onto which electrical circuits are printed for mounting into a comput-
er or electrical device.
A computerized device that can accept inputs from external devices and gen-
erate outputs to external devices according to a program held in memory.
Programmable Controllers are used to automate control of external devices.
Although single-unit Programmable Controllers are available, building-block
Programmable Controllers are constructed from separate components. Such
Programmable Controllers are formed only when enough of these separate
components are assembled to form a functional assembly, i.e., there is no
one individual Unit called a PC.
A peripheral device used to input a program into a PC or to alter or monitor a
program already held in the PC. There are dedicated programming devices,
such as Programming Consoles, and there are non-dedicated devices, such
as a host computer.
An assembly of various Units on a Backplane that forms a functional unit in a
building-block PC System. Racks include CPU Racks, Expansion I/O Racks,
I/O Racks, and Slave Racks.
A word in the LR area that contains data transferred from another PC in a PC
Link System. A read word cannot be written to by the PC.
The forerunner of PCs. In relay-based control, groups of relays are wired to
each other to form control circuits. In a PC, these are replaced by program-
mable circuits.
A wiring method in which Units are wired consecutively in a string. In Link
Systems wired through Link Adapters, the Units are still functionally wired in
series, even though Units are placed on branch lines.
A PC Link System in which there is no PC with more than one PC Link Unit.
A PC Link System that connects only two PCs to each other.
A position on a Rack (Backplane) to which a Unit can be mounted.
A dedicated Unit that is designed for a specific purpose. Special I/O Units
include Position Control Units, High-speed Counter Units, Analog I/O Units,
etc.
The voltage/current that a relay can switch on and off.
The arrangement in which Units in a System are connected.
polling
polling unit
printed circuit board
Programmable Controller
programming device
Rack
read word
relay-based control
series
Single-level PC Link
System
Single-link PC Link System
slot
Special I/O Unit
switching capacity
system configuration