Page 415 - Programmable Logic Controllers, Fifth Edition - Mobile version

binary notations. The binary-coded decimal system is often referred
to as 8421 code. decisions with its operation controlled by a sequence of instructions.
The central processing unit is also referred to as the processor or
Binary word A related group of 1s and 0s that has meaning assigned the CPU.
by position or by numerical value in the binary system of numbers. Channel A designated path for a signal.
Bit An abbreviated term for the words binary digit. The bit is Character A symbol that is one of a larger group of similar symbols
the smallest unit of information in the binary numbering system. and that is used to represent information on a display device. The
It represents a decision between one of two possible and equally likely letters of the alphabet and the decimal numbers are examples of
values or states. It is often used to represent an off or on state as well characters used to convey information.
as a true or false condition. Chassis A rack that serves as an electrical backplane for a PLC
Bit manipulation instructions A family of programmable logic processor and I/O modules.
controller instructions that exchange, alter, move, or otherwise modify Chip A tiny piece of semiconductor material on which electronic
the individual bits or groups of processor data memory words. components are formed. Chips are normally made of silicon and are
Bit storage A user-defined data table area in which bits can be typically less than 1/4 in. square and 1/100 in. thick.
set or reset without directly affecting or controlling output devices. Clear An instruction or a sequence of instructions that removes
However, any storage bit can be monitored as necessary in the all current information from a programmable logic controller’s
user program. memory.
Block diagram A method of representing the major functional Clock A circuit that generates timed pulses to synchronize the timing
subdivisions, conditions, or operations of an overall system, function, of computer operations.
or operation.
Clock rate The speed at which the microprocessor system
Block format Format that uses a box shape to display instructions.
operates.
Block transfer An instruction that copies the contents of one or Closed loop A control system that uses feedback from the process to
more contiguous data memory words to a second contiguous data maintain outputs at a desired level.
memory location; an instruction that transfers data between an
intelligent input/output module or card and specified processor data Coaxial cable A transmission line constructed such that an outer
memory locations. conductor forms a cylinder around a central conductor. An insulating
dielectric separates the inner and outer conductors, and the complete
BOOL A data type that stores the state of a single bit, where 0 assembly is enclosed in a protective outer sheath. Coaxial cables are
equals off and 1 equals on.
not susceptible to external electric and magnetic fields and generate no
Boolean algebra A mathematical shorthand notation that expresses electric or magnetic fields of their own.
logic functions, such as AND, OR, EXCLUSIVE OR, NAND, NOR, Code A system of communications that uses arbitrary groups of
and NOT.
symbols to represent information or instructions. A set of programmed
Branch A parallel logic path within a rung. instructions.
Buffer In software terms, a register or group of registers used Coil Represents the output of a programmable logic controller.
for temporary storage of data; a buffer is used to compensate for In the output devices, it is the electrical coil that, when energized,
transmission rate differences between the transmitter and receiving changes the status of its corresponding contacts.
device. In hardware terms, a buffer is an isolating circuit used to Coil format Format that uses coils to display instructions.
avoid the reaction of one circuit with another.
Comment Text that is included with each PLC ladder rung and is
Bug A system defect or error that causes a malfunction; can be
caused by either software or hardware. used to help individuals understand how the program operates or how
the rung interacts with the rest of the program.
Burn The process by which information is entered into programmable
read-only memory. Communication module Allows the user to connect the PLC to high-
speed local networks that may differ from the network communication
Bus A group of lines used for data transmission or control; power provided with the PLC.
distribution conductors.
Compare An instruction that compares the contents of two designated
Bus topology A network configuration in which all stations are data memory locations of a programmable logic controller for equality
connected in parallel with the communication medium and all stations or inequality.
can receive information from any other station on the network.
Compatibility The ability of various specified units to replace one
Byte A group of adjacent bits usually operated on as a unit, such as another with little or no reduction in capability; the ability of units to
when moving data to and from memory. There are 8 bits per byte. be interconnected and used without modification.
C Complement A logical operation that inverts a signal or bit.
Cascading In the programming of timers and counters, a technique Complementary metal-oxide semiconductor (CMOS) A logic
used to extend the timing or counting range beyond what would base that offers lower power consumption and high-speed operation.
normally be available. This technique involves the driving of one timer Computer Any electronic device that can accept information,
or counter instruction from the output of another, similar instruction. manipulate it according to a set of preprogrammed instructions, and
Cell controller A specialized computer used to control a work cell supply the results of the manipulation.
through multiple paths to the various cell devices. Computer integrated manufacturing (CIM) A manufacturing
Central processing unit (CPU) The electronic circuitry that controls system controlled by an easily reprogrammable computer for flexibility
all the data activity of the PLC, performs calculations, and makes and speed of changeover.

396 Glossary

pet73842_gls_395-406.indd 396 03/11/15 4:09 PM