Pc Terminology - Omron SYSMAC C2000H Operation Manual

PC Terminology

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PC Terminology

PC
Inputs and Outputs
Controlled System and
Control System
Actually there is not a total equivalence between these terms. The term con-
dition is only used to describe ladder diagram programs in general and is
specifically equivalent to one of certain set of basic instructions. The terms
input and output are not used in programming per se, except in reference to
I/O bits that are assigned to input and output signals coming into and leaving
the PC. Normally open conditions and normally closed conditions are ex-
plained in 4-2 The Ladder Diagram.
Although also provided in the Glossary at the back of this manual, the follow-
ing terms are crucial to understanding PC operation and are thus explained
here.
Because the C1000H and C2000H are Rack PCs, there is no one product
that is a C1000H or C2000H PC. That is why we talk about the configuration
of the PC, because a PC is a configuration of smaller Units.
To have a functional PC, you would need to have a CPU Rack with at least
one Unit mounted to it that provides I/O points. With a Duplex System, you
would also need an CPU I/O Rack to mount the I/O Unit, because the Duplex
CPU Rack does not provide slots for mounting other Units. When we refer to
the PC, however, we are generally talking about the CPU and all of the Units
directly controlled by it through the program. This does not include the I/O
devices connected to PC inputs and outputs.
If you are not familiar with the terms used above to describe a PC, refer to
2-2 Hardware Considerations for explanations.
A device connected to the PC that sends a signal to the PC is called an input
device; the signal it sends is called an input signal. A signal enters the PC
through terminals or through pins on a connector on a Unit. The place where
a signal enters the PC is called an input point. This input point is allocated a
location in memory that reflects its status, i.e., either ON or OFF. This mem-
ory location is called an input bit. The CPU, in its normal processing cycle,
monitors the status of all input points and turns ON or OFF corresponding
input bits accordingly.
There are also output bits in memory that are allocated to output points on
Units through which output signals are sent to output devices, i.e., an out-
put bit is turned ON to send a signal to an output device through an output
point. The CPU periodically turns output points ON or OFF according to the
status of the output bits.
These terms are used when describing different aspects of PC operation.
When programming, one is concerned with what information is held in mem-
ory, and so I/O bits are referred to. When talking about the Units that connect
the PC to the controlled system and the places on these Units where signals
enter and leave the PC, I/O points are referred to. When wiring these I/O
points, the physical counterparts of the I/O points, either terminals or connec-
tor pins, are referred to. When talking about the signals that enter or leave
the PC, one refers to input signals and output signals, or sometimes just in-
puts and outputs. It all depends on what aspect of PC operation is being
talked about.
The Control System includes the PC and all I/O devices it uses to control an
external system. A sensor that provides information to achieve control is an
input device that is clearly part of the Control System. The controlled system
is the external system that is being controlled by the PC program through
Section 1-3
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