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Glossary
107
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.
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.
LR area A data area that is used in data links.
LSS See Ladder Support Software.
main program All of a program except for subroutine and interrupt programs.
mark trace A process in which changes in the contents of specific memory locations are re-
corded during program execution.
masked bit A bit whose status has been temporarily made ineffective.
masking ‘Covering’ an interrupt signal so that the interrupt is not effective until the mask is
removed.
megabyte A unit of storage equal to one million bytes.
memory area Any of the areas in the PC used to hold data or programs.
message number A number assigned to a message generated with the MESSAGE instruction.
mnemonic code A form of a ladder-diagram program that consists of a sequential list of the in-
structions without using a ladder diagram.
MONITOR mode A mode of PC operation in which normal program execution is possible, and
which allows modification of data held in memory. Used for monitoring or debug-
ging the PC.
most-significant (bit/word) See leftmost (bit/word).
NC input An input that is normally closed, i.e., the input signal is considered to be present
when the circuit connected to the input opens.
negative delay A delay set for a data trace in which recording data begins before the trace signal
by a specified amount.
nesting Programming one loop within another loop, programming a call to a subroutine
within another subroutine, or programming one jump within another.
NO input An input that is normally open, i.e., the input signal is considered to be present
when the circuit connected to the input closes.
noise interference Disturbances in signals caused by electrical noise.
non-fatal error A hardware or software error that produces a warning but does not stop the PC
from operating.