Glossary
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port
A connector on a PC or computer that serves as a connection to an external
device.
present value
The current value registered in a device at any instant during its operation.
Present value is abbreviated as PV.
printed circuit board
A board onto which electrical circuits are printed for mounting into a comput-
er or electrical device.
Printer Interface Unit
A Unit used to interface a printer so that ladder diagrams and other data can
be printed out.
program
The list of instructions that tells the PC the sequence of control actions to be
carried out.
Programmable Controller
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-component Programmable Controllers are available, build-
ing-block Programmable Controllers are constructed from separate compo-
nents. Such building-block Programmable Controllers are formed only when
enough of these separate components are assembled to form a functional
assembly, i.e., no one individual Unit is called a PC.
programmed alarm
An alarm given as a result of execution of an instruction designed to gener-
ate 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 gen-
erate 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
generate the message in the program, as opposed to one generated by the
system.
Programming Console
The simplest form or programming device available for a PC. Programming
Consoles are available both as hand-held models and as CPU-mounting
models.
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.
PROGRAM mode
A mode of operation that allows inputting and debugging of programs to be
carried out, but that does not permit normal execution of the program.
PROM Writer
A peripheral device used to write programs and other data into a ROM for
permanent storage and application.
prompt
A message or symbol that appears on a display to request input from the op-
erator.
PV
Acronym for present value.
Rack
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.
