Glossary
Programmable Controller
A
computerized device that can accept inputs from external devices and gener-
ate outputs to external devices according to a program held in memory. Pro-
grammable Controllers are used to automate control of external devices. Al-
though single-unit Programmable Controllers are available, building-block Pro
grammable Controllers are constructed from separate components. Such Pro
grammable Controllers are formed only when enough of these separate compo
nents are assembled to form a functional assembly, i.e., there is no one individu
al Unit called a PC.
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Programming Console
Programming Device
The simplest form or programming device available for a PC. Programming
Consoles are available both as hand-held models and as CPU-mounting mod
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els.
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.
PROM
Programmable read-only memory; a type of ROM into which the program or
data may be written after manufacture, by a customer, but which is fixed from
that time on.
PROM Writer
prompt
A
peripheral device used to write programs and other data into a ROM for per
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manent storage and application.
A
message or symbol that appears on a display to request input from the opera
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tor.
protocol
The parameters and procedures that are standardized to enable two devices to
communicate or to enable a programmer or operator to communicate with a de
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vice.
PV
See present value.
Rack
An assembly that forms a functional unit in a Rack PC System. A Rack consists
of a Backplane and the Units mounted to it. These Units include the Power Sup
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ply, CPU, and I/O Units. Racks include CPU Racks, Expansion I/O Racks, and
I/O Racks. The CPU Rack is the Rack with the CPU mounted to it. An Expansion
I/O Rack is an additional Rack that holds extra I/O Units. An I/O Rack is used in
the C2000H Duplex System, because there is no room for any I/O Units on the
CPU Rack in this System.
rack number
Rack PC
A
number assigned to a Rack according to the order that it is connected to the
CPU Rack, with the CPU Rack generally being rack number 0.
A
PC that is composed of Units mounted to one or more Racks. This configura
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tion is the most flexible, and most large PCs are Rack PCs. A Rack PC is the
opposite of a Package-type PC, which has all of the basic I/O, storage, and con
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trol functions built into a single package.
RAM
Random access memory; a data storage media. RAM will not retain data when
power is disconnected.
RAS
An acronym for reliability, assurance, safety.
refresh
The process of updating output status sent to external devices so that it agrees
with the status of output bits held in memory and of updating input bits in memory
so that they agree with the status of inputs from external devices.
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