22.3 PROGRAM DESIGN METHODS

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NOTE: these are structured design methods - although many of the design activities are obvious, by following the same steps, others can understand what you have done, and others will get similar results when they solve a similar problem. This is a simple start, and we will advance to significant design techniques later.

22.3.1 Process Sequence Bits

A simple process will typically go through clear steps. Each step should follow the other, and when done the process goes back to the beginning.

The general steps to this method are,

1. Understand the process

2. Write the steps of operation and give each a number

3. For each step assign a bit

4. Write the ladder logic to turn the bits on/off as the process moves through its states.

Consider the problem below.

22.3.2 Timing Diagrams

By writing a timing diagram, the sequence of steps in a program can be obvious.

The general steps to this method are,

1. Understand the process

2. Identify the outputs that are time dependant

3. For each step assign a timer

4. Write the ladder logic to turn the outputs on/off as time progresses.

Consider the problem below.