Glossary
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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 dia-
gram and are called terminal instructions.
Ladder Support Software
A software package that provides most of the functions of the Factory Intelli-
gent Terminal on an IBM AT, IBM XT, or compatible computer.
LAN
An acronym for local area network.
leftmost (bit/word)
The highest numbered bits of a group of bits, generally of an entire word, or
the highest numbered words of a group of words. These bits/words are often
called most-significant bits/words.
Link Adapter
A Unit used to connect communications lines, either to branch the lines or to
convert between different types of cable. There are two types of Link
Adapter: Branching Link Adapters and Converting Link Adapters.
link
A hardware or software connection formed between two Units. “Link” can
refer either to a part of the physical connection between two Units (e.g., opti-
cal links in Wired Remote I/O Systems) or a software connection created to
data existing at another location (Network Data Links).
linkable slot
A slot on either a CPU or Expansion I/O Backplane to which a Link Unit can
be mounted. Backplanes differ in the slots to which Link Units can be
mounted.
Link System
A system that includes one or more of the following systems: Remote I/O
System, PC Link System, Host Link System, or SYSMAC NET Link System.
Link Unit
Any of the Units used to connect a PC to a Link System. These are Remote
I/O Units, I/O Link Units, PC Link Units, Host Link Units, and SYSMAC NET
Link Units.
load
The processes of copying data either from an external device or from a stor-
age area to an active portion of the system such as a display buffer. Also, an
output device connected to the PC is called a load.
local area network
A network consisting of nodes or positions in a loop arrangement. Each node
can be any one of a number of devices, which can transfer data to and from
each other.
logic block
A group of instructions that is logically related in a ladder-diagram program
and that requires logic block instructions to relate it to other instructions or
logic blocks.
logic block instruction
An instruction used to locally combine the execution condition resulting from
a logic block with a current execution condition. The current execution condi-
tion could be the result of a single condition, or of another logic block. AND
Load and OR Load are the two logic block instructions.
logic instruction
Instructions used to logically combine the content of two words and output
the logical results to a specified result word. The logic instructions combine
all the same-numbered bits in the two words and output the result to the bit of
the same number in the specified result word.