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Glossary
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Remote I/O System A system in which remote I/O points are controlled through a Master mounted to
a CPU Rack or an Expansion I/O Rack connected to the CPU Rack.
Remote I/O Unit Any of the Units in a Remote I/O System. Remote I/O Units include Masters,
Slaves, Optical I/O Units, I/O Link Units, and Remote Terminals.
remote I/O word An I/O word allocated to a Unit in a Remote I/O System.
reset The process of turning a bit or signal OFF or of changing the present value of a
timer or counter to its set value or to zero.
return The process by which instruction execution shifts from a subroutine back to the
main program (usually the point from which the subroutine was called).
reversible counter A counter that can be both incremented and decremented depending on the
specified conditions.
reversible shift register A shift register that can shift data in either direction depending on the specified
conditions.
right-hand instruction Another term for terminal instruction.
rightmost (bit/word) The lowest numbered bits of a group of bits, generally of an entire word, or the
lowest numbered words of a group of words. These bits/words are often called
least-significant bits/words.
rotate register A shift register in which the data moved out from one end is placed back into the
shift register at the other end.
RUN mode The operating mode used by the PC for normal control operations.
scheduled interrupt An interrupt that is automatically generated by the system at a specific time or
program location specified by the operator. Scheduled interrupts result in the
execution of specific subroutines that can be used for instructions that must be
executed repeatedly for a specified period of time.
self diagnosis A process whereby the system checks its own operation and generates a warn-
ing or error if an abnormality is discovered.
self-maintaining bit A bit that is programmed to maintain either an OFF or ON status until set or reset
by specified conditions.
servicing The process whereby the PC provides data to or receives data from external de-
vices or remote I/O Units, or otherwise handles data transactions for Link Sys-
tems.
set The process of turning a bit or signal ON.
set value The value from which a decrementing counter starts counting down or to which
an incrementing counter counts up (i.e., the maximum count), or the time from
which or for which a timer starts timing. Set value is abbreviated SV.
shift register One or more words in which data is shifted a specified number of units to the right
or left in bit, digit, or word units. In a rotate register, data shifted out one end is
shifted back into the other end. In other shift registers, new data (either specified
data, zero(s) or one(s)) is shifted into one end and the data shifted out at the oth-
er end is lost.