How do you use state diagrams and state tables to design and document your control logic?

1 What is a state machine?

A state machine is a model of a system that can be in one of a finite number of states at any given time. Each state represents a specific configuration of the system, such as its output values, internal variables, or mode of operation. A state machine can change its state in response to external or internal events, such as input signals, timers, or conditions. The state transitions are defined by a set of rules or logic that specify when and how the state machine moves from one state to another.

2 Why use state diagrams and state tables?

State diagrams and state tables are two common ways of representing a state machine graphically or textually. They can help you design, document, and communicate your state machine logic in a clear and concise way. A state diagram is a visual representation of the states and transitions of a state machine, using circles for states and arrows for transitions. A state table is a tabular representation of the same information, using rows for states and columns for inputs and outputs. Both methods have their advantages and disadvantages, depending on the complexity and size of your state machine.

3 How to create a state diagram?

To create a state diagram, you must first identify the states of your system and label them with meaningful names, or assign numbers or codes for easier reference. You should also identify the inputs and outputs of your system and label them accordingly. Then, draw a circle for each state and write the state name or number inside it, along with any output values or actions associated with each state outside the circle. Draw an arrow for each transition between states and write the input values or events that trigger the transition along the arrow, using conditions or expressions to specify complex logic if necessary. Finally, choose a starting state and mark it with an arrow pointing to it from nowhere - this is the initial state of your system.

4 How to create a state table?

Creating a state table requires identifying the states, inputs, and outputs of your system, and constructing a table with one row for each state and one column for each input and output. You can also include a column for the state name or number for easier reference. Then, fill in the table with the output values or actions for each state in the corresponding columns, as well as the next state for each state and input combination. Additionally, you should choose a starting state and mark it with an asterisk (*) or other symbol to indicate that it is the initial state of your system.

5 How to optimize your state machine design?

To make your state machine design more efficient, reliable, and maintainable, there are several techniques you can apply. Minimizing the number of states and transitions is a good place to start, as is simplifying the logic and conditions for the transitions. Additionally, it’s important to use consistent and meaningful naming conventions for your states, inputs, and outputs. Comments and annotations can help explain your logic and assumptions, while testing and verifying your design with simulation tools or test cases will ensure it works as intended.