Glossary
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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.
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.
programmed alarm An alarm given as a result of execution of an instruction designed to generate the
alarm in the program, as opposed to one generated by the system.
programmed error An error arising as a result of the execution of an instruction designed to gener-
ate the error in the program, as opposed to one generated by the system.
programmed message A message generated as a result of execution of an instruction designed to gen-
erate the message in the program, as opposed to one generated by the system.
Programming Console The portable form of Programming Device for a PC.
Programming Device 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.
prompt A message or symbol that appears on a display to request input from the opera-
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
device.
PV See
present value
.
RAM Random access memory; a data storage media. RAM will not retain data when
power is disconnected.
RAS An acronym for reliability, assurance, safety.
read-only area A memory area from which the user can read status but to which data cannot be
written.
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.
relay-based control The forerunner of PCs. In relay-based control, groups of relays are intercon-
nected to form control circuits. In a PC, these are replaced by programmable cir-
cuits.
reserved bit A bit that is not available for user application.
reserved word A word in memory that is reserved for a special purpose and cannot be accessed
by the user.
reset The process of turning a bit or signal OFF or of changing the present value of a
timer or counter to its set value or to zero.
response code A code sent with the response to a data transmission that specifies how the
transmitted data was processed.
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