Glossary
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system error An error generated by the system, as opposed to one resulting from execution of
an instruction designed to generate an error.
system error message An error message generated by the system, as opposed to one resulting from
execution of an instruction designed to generate a message.
terminal instruction An instruction placed on the right side of a ladder diagram that uses the final ex-
ecution conditions of an instruction line.
terminator The code comprising an asterisk and a carriage return (* CR) which indicates the
end of a block of data in communications between devices. Frames within a mul-
ti-frame block are separated by delimiters. Also a Unit in a Link System desig-
nated as the last Unit on the communications line.
timer A location in memory accessed through a TC bit and used to time down from the
timer’s set value. Timers are turned ON and reset according to their execution
conditions.
TR Area A data area used to store execution conditions so that they can be reloaded later
for use with other instructions.
TR bit A bit in the TR Area.
trace An operation whereby the program is executed and the resulting data is stored to
enable step-by-step analysis and debugging.
trace memory A memory area used to store the results of trace operations.
transfer The process of moving data from one location to another within the PC, or be-
tween the PC and external devices. When data is transferred, generally a copy
of the data is sent to the destination, i.e., the content of the source of the transfer
is not changed.
transition A status in a SFC program that determines when active status is transferred
from one step to another. Transitions can be defined either as the status of a bit
or as an execution condition resulting from a ladder diagram.
Transition Area A memory area that contains Transition Flags.
Transition Flag A flag that indicates when a transition is ON or OFF.
transition number A number assigned to a transition and used to access its Transition Flag.
transmission distance The distance that a signal can be transmitted.
trigger A signal used to activate some process, e.g., the execution of a trace operation.
trigger address An address in the program that defines the beginning point for tracing. The ac-
tual beginning point can be altered from the trigger by defining either a positive or
negative delay.
UM area The memory area used to hold the active program, i.e., the program that is being
currently executed.
Unit In OMRON PC terminology, the word Unit is capitalized to indicate any product
sold for a PC System. Though most of the names of these products end with the
word Unit, not all do, e.g., a Remote Terminal is referred to in a collective sense
as a Unit. Context generally makes any limitations of this word clear.
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