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Glossary
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I/O Control Unit A Unit mounted to the CPU Rack in certain PCs to monitor and control I/O points
on Expansion I/O Units.
I/O devices The devices to which terminals on I/O Units, Special I/O Units, or Intelligent I/O
Units are connected. I/O devices may be either part of the Control System, if they
function to help control other devices, or they may be part of the controlled sys-
tem.
I/O Interface Unit A Unit mounted to an Expansion I/O Rack in certain PCs to interface the Expan-
sion I/O Rack to the CPU Rack.
I/O Link Created in an Optical Remote I/O System to enable input/output of one or two IR
words directly between PCs. The words are input/output between the PC con-
trolling the Master and a PC connected to the Remote I/O System through an I/O
Link Unit or an I/O Link Rack.
I/O Link Unit A Unit used with certain PCs to create an I/O Link in an Optical Remote I/O Sys-
tem.
I/O point The place at which an input signal enters the PC System, or at which an output
signal leaves the PC System. In physical terms, I/O points correspond to termi-
nals or connector pins on a Unit; in terms of programming, an I/O points corre-
spond to I/O bits in the IR area.
I/O response time The time required for an output signal to be sent from the PC in response to an
input signal received from an external device.
I/O table A table created within the memory of the PC that lists the IR area words allocated
to each Unit in the PC System. The I/O table can be created by, or modified from,
a Programming Device.
I/O Unit The most basic type of Unit mounted to a backplane to create a Rack. I/O Units
include Input Units and Output Units, each of which is available in a range of
specifications. I/O Units do not include Special I/O Units, Link Units, etc.
I/O word A word in the IR area that is allocated to a Unit in the PC System.
IR area A data area whose principal function is to hold the status of inputs coming into
the system and that of outputs that are to be set out of the system. Bits and words
in the IR that are used this way are called I/O bits and I/O words. The remaining
bits in the IR area are work bits.
JIS 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 inbetween.
Jumps are usually conditional on an execution condition.
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 a ladder-diagram program.
ladder instruction An instruction that represents the ‘rung’ portion of a ladder-diagram program.
The other instructions in a ladder diagram fall along the right side of the diagram
and are called terminal instructions.