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Glossary
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 other end is lost.
signed binary A binary value that is stored in memory along with a bit that indicates whether
the value is positive or negative.
software error An error that originates in a software program.
software protect A means of protecting data from being changed that uses software as opposed
to a physical switch or other hardware setting.
source (word) 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 instruction An instruction input with a function code that handles data processing opera-
tions within ladder diagrams, as opposed to a basic instruction, which makes
up the fundamental portion of a ladder diagram.
SR area A memory area containing flags and other bits/words with specific functions.
SSS See SYSMAC Support Software.
store The process of recording a program written into a display buffer permanently
in memory.
subroutine A group of instructions placed separate from the main program and executed
only when 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 acti-
vates.
subtract count input An input signal used to decrement a counter when the signal changes from
OFF to ON.
SV See set value.
switching capacity The maximum voltage/current that a relay can safely switch on and off.
synchronous execution Execution of programs and servicing operations in which program execution
and servicing are synchronized so that all servicing operations are executed
each time the programs are executed.
syntax The form of a program statement (as opposed to its meaning).
syntax error An error in the way in which a program is written. Syntax errors can include
‘spelling’ mistakes (i.e., a function code that does not exist), mistakes in spec-
ifying operands within acceptable parameters (e.g., specifying read-only bits
as a destination), and mistakes in actual application of instructions (e.g., a call
to a subroutine that does not exist).
SYSMAC Support Software A software package installed on a IBM PC/AT or compatible computer to func-
tion as a Programming Device.
system configuration The arrangement in which Units in a System are connected. This term refers
to the conceptual arrangement and wiring together of all the devices needed
to comprise the System.
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.
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