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Glossary
540
bit designator An operand that is used to designate the bit or bits of a word to be used by an
instruction.
bit number A number that indicates the location of a bit within a word. Bit 00 is the rightmost
(least-significant) bit; bit 15 is the leftmost (most-significant) bit.
building-block PC A PC that is constructed from individual components, or “building blocks.” With
building-block PCs, there is no one Unit that is independently identifiable as a
PC. The PC is rather a functional assembly of components.
bus bar The line leading down the left and sometimes right side of a ladder diagram.
Instruction execution proceeds down the bus bar, which is the starting point for
all instruction lines.
call A process by which instruction execution shifts from the main program to a sub-
routine. The subroutine may be called by an instruction or by an interrupt.
carry flag A flag that is used with arithmetic operations to hold a carry from an addition or
multiplication operation, or to indicate that the result is negative in a subtraction
operation. The carry flag is also used with certain types of shift operations.
clock pulse A pulse available at a certain bit in memory for use in timing operations. Various
clock pulses are available with different pulse widths.
clock pulse bit A bit in memory that supplies a pulse that can be used to time operations. Vari-
ous clock pulse bits are available with different pulse widths, and therefore differ-
ent frequencies.
common data Data that is stored in the LR Area of a PC and which is shared by other PCs in the
same system. Each PC has a specified section of the LR Area allocated to it.
This allocation is the same in each LR Area of each PC.
Communications Board A board that is mounted to the optional slot of a C200HX/HG/HE CPU Unit. With
a Communications Board, the CPU Unit can communicate with the SYSMAC
LINK Unit, SYSMAC NET Link Unit, Programmable Terminal, Temperature Con-
troller, personal computer, bar code reader, or any other peripheral device via
RS-232C, RS-422, or RS-485.
condition An message placed in an instruction line to direct the way in which the terminal
instructions, on the right side, are to be executed. Each condition is assigned to a
bit in memory that determines its status. The status of the bit assigned to each
condition determines, in turn, the execution condition for each instruction up to a
terminal instruction on the right side of the ladder diagram.
constant An operand for which the actual numeric value is specified by the user, and
which is then stored in a particular address in the data memory.
control bit A bit in a memory area that is set either through the program or via a Program-
ming Device to achieve a specific purpose, e.g., a Restart bit is turned ON and
OFF to restart a Unit.
Control System All of the hardware and software components used to control other devices. A
Control System includes the PC System, the PC programs, and all I/O devices
that are used to control or obtain feedback from the controlled system.
controlled system The devices that are being controlled by a PC System.
control signal A signal sent from the PC to effect the operation of the controlled system.