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Glossary
absolute position A position given in respect to the origin rather than in respect to the present posi-
tion.
acceleration/deceleration curve Curves which determine the rate of acceleration to the maximum feed rate and
the rate of deceleration from the maximum feed rate.
auxiliary bit A bit in the Auxiliary Area.
Backplane A base to which Units are mounted to form a Rack. Backplanes provide a series
of connectors for these Units along with buses to connect them to the CPU and
other Units and wiring to connect them to the Power Supply Unit. Backplanes
also provide connectors used to connect them to other Backplanes.
basic instruction A fundamental instruction used in a ladder diagram. See advanced instruction.
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
hexadecimal digit. Binary data in memory is thus often expressed in hexadeci-
mal for convenience.
bit The smallest piece of information that can be represented on a computer. A bit
has the value of either zero or one, corresponding to the electrical signals ON
and OFF. A bit represents one binary digit. Some bits at particular addresses are
allocated to special purposes, such as holding the status of input from external
devices, while other bits are available for general use in programming.
block number Numbers used to distinguish blocks in MC programs. Block numbers are roughly
equivalent to program line numbers.
bus A communications path used to pass data between any of the Units connected
to it.
channel See word.
comment block A program block that contains comments input by the programmer. Comment
blocks and program blocks share the same block numbers, but comment blocks
begin with an asterisk rather than an “N.”
control bit A bit in a memory area that is set either through the program or via a Program-
ming Device to achieve a specific purpose, e.g., a Restart Bit is turned ON and
OFF to restart a Unit.
counter A dedicated group of digits or words in memory used to count the number of
times a specific process has occurred, or a location in memory accessed
through a TC bit and used to count the number of times the status of a bit or an
execution condition has changed from OFF to ON.
CPU The name of the Unit in a PC that contains the main CPU and other main PC
components. See also central processing unit.
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