Glossary
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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.
software switch See
memory switch
.
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 I/O Unit A Unit that is designed for a specific purpose. Special I/O Units include Position
Control Units, High-speed Counter Units, Analog I/O Units, etc.
SRAM Static random access memory; a data storage media.
stack instruction An instruction that manipulates data in a stack.
stack pointer The register which points to the top of the stack. See
stack
and
pointer
.
step A basic unit of execution in an SFC program. Steps are used to organize an SFC
program by process and control the overall flow of program execution.
Step Area A memory area that contains a flag that indicates the status of steps in an SFC
program.
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.
SV Abbreviation for set value.
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). For example, the
two statements, LET A=B+B and LET A=B*2 use different syntaxes, but have
the same 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 specify-
ing 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).
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. In OMRON terminology, system configuration is used to
describe the arrangement and connection of the Units comprising a Control Sys-
tem that includes one or more PCs.
System DM A dedicated portion of the DM area that is used for special purposes in control-
ling and managing the PC. Includes the Program Version, Parameter Area, Pa-
rameter Backup Area, User Program Header, and Error Log Area.
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