1.3 PROGRAM DESIGN METHODS

• 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.

1.3.1 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.

 

 

 

1.3.2 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.