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Glossary
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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
devices or remote I/O Units, or otherwise handles data transactions for Link
Systems.
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 (ei-
ther specified data, zero(s) or one(s)) is shifted into one end and the data
shifted out at the other end is lost.
Simplex CPU
A C2000H PC that uses only a single CPU as opposed to a Duplex CPU.
This term is meaningless with other PCs, which are only available with sim-
plex operation.
Simplex System
A C2000H PC System that uses a Simplex CPU.
Slave
Short for Remote I/O Slave Unit.
Slave Rack
A Rack containing a Remote I/O Slave Unit and controlled through a Remote
I/O Master Unit. Slave Racks are generally located away from the CPU Rack.
slot
A position on a Rack (Backplane) to which a Unit can be mounted.
software error
An error that originates in a software program.
software protect
A means of protecting data from being changed that uses software as op-
posed 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 latter is
called the destination.
Special I/O Unit
A dedicated Unit that is designed for a specific purpose. Special I/O Units
include Position Control Units, High-Speed Counter Units, Analog I/O Units,
ASCII Units, Ladder Diagram I/O Units, etc.
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.