Filter
Top Products
Glossary
546
ladder diagram (program) A form of program arising out of relay-based control systems that uses circuit-
type diagrams to represent the logic flow of programming instructions. The ap-
pearance 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.
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 con-
vert 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., optical 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 Sys-
tem, PC Link System, Host Link System, or 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 Net Link Units.
load The processes of copying data either from an external device or from a storage
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 condition
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.
loop A group of instructions that can be executed more than once in succession (i.e.,
repeated) depending on an execution condition or bit status.