Chapter 3 Introduction To Programming; Overview; Relay Ladder Diagram Method; Eight Basic Programming Steps - Omron SYSMAC C Series User Manual

Chapter 3 Introduction to programming
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Overview
This chapter introduces the eight steps you'll take in creating the program
the PC uses to carry out its control operations. You can skip this chapter if
you're already familiar with PC programming using relay ladder dia-
grams. Instead, you may wish to go directly to Chapters 4 and 5 which
focus on how the C20 programming console is used to install the program
in the memory of the CPU.
Relay ladder diagram method
If you're an old hand at relay-based control systems, you'll find a lot that's
familiar in the way a PC works. This is because the circuits and internal
logic of the PC take the place of the relays, timers, counters, and other
formerly discrete devices. The actual operation of the machinery takes
place as if those discrete devices were still in place, but with a great deal
more flexibility and reliability.
But even if the actual devices are gone, the symbols and other control
concepts used to describe their operation still are used. These are the
basis of the relay ladder diagram programming method. This chapter has
been written on the assumption that you are already experienced with this
relay symbology, or have access to information that can teach you about
it.
Eight basic programming steps
In creating the control program for the PC, you'll foliow these eight basic
steps:
1. Determine what the controlled system must do and in what order.
2. Assign input and output devices, that is, designate the external
devices that will send signals to and receive signals from the PC.
3. Draw a diagram, using relay ladder symbols. This represents, in the
correct sequence, all of the required functions and their relationship.
4. Code the ladder symbols into a form that can be input to the CPU by
the programming console.
5. Transfer these written instructions to the CPU via the programming
console.
6. Edit the program.
7. Test the program for errors.
8. Save the completed program.
Steps 1 through 4 are the focus of this chapter.