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Glossary
address A number used to identify the location of data or programming instructions in
memory or to identify the location of a network or a Unit in a network.
advanced instruction An instruction input with a function code that handles data processing opera-
tions within ladder diagrams, as opposed to a basic instruction, which makes up
the fundamental portion of a ladder diagram.
allocation The process by which the PC assigns certain bits or words in memory for various
functions. This includes pairing I/O bits to I/O points on Units.
analog Something that represents or can process a continuous range of values as op-
posed to values that can be represented in distinct increments. Something that
represents or can process values represented in distinct increments is called
digital.
Analog I/O Unit I/O Units that convert I/O between analog and digital values. An Analog Input
Unit converts an analog input to a digital value for processing by the PC. An Ana-
log Output Unit converts a digital value to an analog output.
AND A logic operation whereby the result is true if and only if both premises are true.
In ladder-diagram programming the premises are usually ON/OFF states of bits
or the logical combination of such states called execution conditions.
area See data area and memory area.
area prefix A one or two letter prefix used to identify a memory area in the PC. All memory
areas except the CIO area require prefixes to identify addresses in them.
ASCII Short for American Standard Code for Information Interchange. ASCII is used to
code characters for output to printers and other external devices.
asynchronous execution Execution of programs and servicing operations in which program execution
and servicing are not synchronized with each other.
Auxiliary Area A PC data area allocated to flags and control bits.
auxiliary bit A bit in the Auxiliary Area.
back-up A copy made of existing data to ensure that the data will not be lost even if the
original data is corrupted or erased.
BASIC A common programming language. BASIC Units are programmed in BASIC.
basic instruction A fundamental instruction used in a ladder diagram. See advanced instruction.
BASIC Unit A CPU Bus Unit used to run programs in BASIC.
baud rate The data transmission speed between two devices in a system measured in bits
per second.
BCD Short for binary-coded decimal.
binary A number system where all numbers are expressed in base 2, i.e., numbers are
written using only 0’s and 1’s. Each group of four binary bits is equivalent to one
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