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Glossary
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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.
RUN mode The operating mode used by the PC for normal control operations.
scan time
See cycle time.
self diagnosis A process whereby the system checks its own operation and generates a
warning 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 a specific condition(s) different from the one that originally caused
the bit to turn OFF or ON.
servicing The process whereby the PC provides data to or receives data from external
devices or remote I/O or otherwise handles data transactions for Link Sys-
tems.
set The process of turning a bit or signal ON.
set value The count from which a counter starts counting down (or, in the case of a
reversible counter, the maximum count) or the time from which a timer starts
timing. Set value is abbreviated SV.
shift register One or more words in which data is shifted in bit, digit, or word units a speci-
fied number of units to the right or left.
Slave Short for Remote I/O Slave Unit.
Slave Rack A C200H, C500, C1000H, or C2000H Rack containing a Remote I/O Slave
Unit and controlled through a Remote I/O Master Unit. Slave Racks are gen-
erally located away from the CPU Rack.
software error An error that occurs in the execution of a program.
software protects A software means of protecting data from being changed as opposed to a
physical switch or other hardware setting.
source The location from which data is taken for use in an instruction as opposed to
the location to which the result of an instruction is to be written. The location
to which the result of an instruction is to be written is called the destination.
SR area A data area in a PC used mainly for flags, control bits, and other information
provided about PC operation. The status of only certain SR bits may be con-
trolled by the operator, i.e., most SR bits can only be read.
subroutine A group of instructions placed after the main program and executed only if
called from the main program or activated by an interrupt.
subroutine number A definer used to identify the subroutine that a subroutine call or interrupt
activates.