Glossary
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instruction block A group of instructions that is logically related in a ladder-diagram program. A
logic block includes all of the instruction lines that interconnect with each other
from one or more line connecting to the left bus bar to one or more right-hand
instructions connecting to the right bus bar.
instruction execution time The time required to execute an instruction. The execution time for any one in-
struction can vary with the execution conditions for the instruction and the oper-
ands used in it.
instruction line A group of conditions that lie together on the same horizontal line of a ladder dia-
gram. Instruction lines can branch apart or join together to form instruction
blocks. Also called a rung.
interface An interface is the conceptual boundary between systems or devices and usual-
ly involves changes in the way the communicated data is represented. Interface
devices such as NSBs perform operations like changing the coding, format, or
speed of the data.
interlock A programming method used to treat a number of instructions as a group so that
the entire group can be reset together when individual execution is not required.
An interlocked program section is executed normally for an ON execution condi-
tion and partially reset for an OFF execution condition.
intermediate instruction An instruction other than one corresponding to a condition that appears in the
middle of an instruction line and requires at least one more instruction between it
and the right bus bar.
interrupt (signal) A signal that stops normal program execution and causes a subroutine to be run
or other processing to take place.
Interrupt Input Unit A Rack-mounting Unit used to input external interrupts into a PC System.
interrupt program A program that is executed in response to an interrupt.
inverse condition See
normally closed condition
.
IOIF An acronym for I/O Interface Unit.
IOM (Area) A collective memory area containing all of the memory areas that can be ac-
cessed by bit, including timer and counter Completion Flags. The IOM Area in-
cludes all memory area memory addresses between 0000 and 0FFF.
JIS An acronym for Japanese Industrial Standards.
jump A type of programming where execution moves directly from one point in a pro-
gram to another, without sequentially executing any instructions in between.
Jumps in ladder diagrams are usually conditional on an execution condition;
jumps in SFC programs are conditional on the step status and transition condi-
tion status before the jump.
jump number A definer used with a jump that defines the points from and to which a jump is to
be made.
ladder diagram (program) A form of program arising out of relay-based control systems that uses cir-
cuit-type diagrams to represent the logic flow of programming instructions. The
appearance of the program is similar to a ladder, and thus the name.
ladder diagram symbol A symbol used in drawing a ladder-diagram program.
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