4
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
memory, 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 con-
nector 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 inputs and outputs. It all depends on what aspect of PC operation is be-
ing 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
these I/O devices. I/O devices can sometimes be considered part of the con-
trolled system, e.g., a motor used to drive a conveyor belt.
1-2-2
Overview of PC Operation
The following are the basic steps involved in programming and operating the
SP-series PCs. Assuming you have already purchased one or more of these
PCs, you must have a reasonable idea of the required information for steps
one and two, which are discussed briefly below. The rest of the steps are de-
scribed later in this manual.
1, 2, 3.. 1.
Determine what the controlled system must do, in what order, and at
what times.
2.
Determine what size of system is required, i.e.,will a single CPU suffice
or will a Link Adapter be required to join multiple CPUs.
3.
On paper, assign all input and output devices to I/O points on the CPUs
and determine which I/O bits will be allocated to each. (3-2 Memory
Areas)
4.
Using relay ladder symbols, write a program that represents the se-
quence of required operations and their inter-relationships. Be sure to
also program appropriate responses for all possible emergency situa-
tions. (3-4 Basic Programming, 3-6 Advanced Programming, and 3-7
Instruction Set)
5.
Input the program and all required data into the PC. (3-5 Inputting the
Program)
6.
Debug the program, first to eliminate any syntax errors, and then to find
execution errors.(3-8 Debugging)
7.
Wire the PC to the controlled system. (Section 2 Installation)
8.
Test the program in an actual control situation and carry out fine tuning
as required. (Section 4 Operation)
9.
Record two copies of the finished program on masters and store them
safely in different locations.(3-5-8 Program Transfer)
Designing the Control System is the first step in automating any process. A
PC can be programmed and operated only after the overall Control System is
understood. Designing the Control System requires, first of all, a thorough
understanding of the devices that are to be controlled. The first step in de-
Controlled System and
Control System
Control System Design
PC Basics
Section 1-2