Glossary
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instruction line A group of conditions that lie together on the same horizontal line of a ladder
diagram. Instruction lines can branch apart or join together to form instruction
blocks.
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 condition and partially reset for an OFF execution condition.
I/O capacity The number of inputs and outputs that a PC is able to handle. This number
ranges from around 10 for smaller PCs to two thousand for the largest ones.
I/O devices The devices to which terminals on I/O Units or Special I/O Units, or other
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 con-
trolled system.
I/O point The place at which an input signal enters the PC System, or at which an out-
put signal leaves the PC System. In physical terms, I/O points correspond to
terminals or connector pins on a Unit; in terms of programming, an I/O points
correspond to I/O bits in memory.
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.
JIS Acronym for Japanese Industrial Standards.
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 dia-
gram and are called terminal instructions.
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 up to four CPUs to enable created data links in the LR
area.
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
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