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Glossary
208
nonfatal error A hardware or software error that produces a warning but does not stop the
PC from operating.
normally closed condition A condition that produces an ON execution condition when the bit assigned
to it is OFF, and an OFF execution condition when the bit assigned to it is
ON.
normally open condition A condition that produces an ON execution condition when the bit assigned
to it is ON and an OFF execution condition when the bit assigned to it is OFF.
NOT A logic operation which inverts the status of the operand. For example, AND
NOT indicates an AND with the opposite of the actual status of the operand
bit.
OFF The status of an input or output when a signal is said not to be present. The
OFF state is generally low voltage or non-conductivity, but can be defined as
the opposite of either.
OFF delay The delay produced between the time turning OFF a signal is initiated (e.g.,
by an input device or PC) and the time the signal reaches a state readable as
an OFF signal (i.e., as no signal) by a receiving party (e.g., output device or
PC).
ON The status of an input or output when a signal is said to be present. The ON
state is generally high voltage or conductivity, but can be defined as the op-
posite of either.
ON delay The delay produced between the time a signal is initiated (e.g., by an input
device or PC) and the the time the signal reaches a state readable as an ON
signal by a receiving party (e.g., output device or PC).
one-shot bit A bit that is turned ON or OFF for a specified interval of time longer than one
cycle.
operand A bit(s) or word(s) designated as the data to be used for an instruction. An
operand can be input as a constant expressing the actual numeric value to
be used or as an address to express the location in memory of the data to be
used.
operand bit A bit designated as an operand for an instruction.
operand word A word designated as an operand for an instruction.
operating error An error that occurs during actual PC operation as opposed to an initializa-
tion error, which occurs before actual operations can begin.
Optical Slave Rack A Slave Rack connected through an Optical Remote I/O Slave Unit.
OR A logic operation whereby the result is true if either one or both of the prem-
ises is true. In ladder-diagram programming the premises are usually ON/
OFF states of bits or the logical combination of such states called execution
conditions.
output The signal sent from the PC to an external device. Output often is used ab-
stractly or collectively to refer to outgoing signals.