Glossary
44
Racks, and I/O Racks. The CPU Rack is the Rack with the CPU mounted to
it. An Expansion I/O Rack is an additional Rack that holds extra I/O Units. An
I/O Rack is used in the C2000H Duplex System, because there is no room
for any I/O Units on the CPU Rack in this System.
Rack PC A PC that is composed of Units mounted to one or more Racks. This configu-
ration is the most flexible, and most large PCs are Rack PCs. A Rack PC is
the opposite of a Package-type PC, which has all of the basic I/O, storage,
and control functions built into a single package.
refresh The process of updating output status sent to external devices so that it
agrees with the status of output bits held in memory and of updating input
bits in memory so that they agree with the status of inputs from external de-
vices.
reset The process of turning a bit or signal OFF or of changing the present value of
a timer or counter to its set value or to zero.
RUN mode The operating mode used by the PC for normal control operations.
scan The process used to execute a ladder-diagram program. The program is ex-
amined sequentially from start to finish and each instruction is executed in
turn based on execution conditions.
scan time The total time it takes the PC to perform internal operations, i.e., reset the
watchdog timer, read the program, receive input data, send output data, and
execute instructions. Scan time is monitored by the watchdog timer within the
PC, and if it takes longer than a certain specified amount of time, an error
message may be generated, or the CPU may just stop. Scan times will differ
depending on the configuration of the system.
sensor An input device that “senses” a property of the real world and relays it to the
Control System. The property can be a measurement of an object, or simply
a signal indicating the presence of the object.
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.
Special I/O Unit A dedicated Unit that is designed for a specific purpose. Special I/O Units
include Position Control Units, High-Speed Counters, Analog I/O Units, etc.
switch An input device that sends either an ON or OFF signal to the Control System.
A switch can be operated either by a person or by the movement of a piece
of equipment or material.
TC area A data area that can be used only for timers and counters. Each bit in the TC
area serves as the access point for the SV, PV, and Completion flag for the
timer or counter defined with that bit.
TC number A definer that corresponds to a bit in the TC area and used to define the bit
as either a timer or counter.
TM area A memory area used to store the results of a trace.
To Next Page
Loading...
