State Diagram Basics
During the design phase of any digital circuit such as synchronous counter, decoder or encoder it is important to plan the outputs that are required by the design specifications. Along with the outputs, inputs signals are also considered. The inputs and the corresponding outputs are first noted down in a neat systematic way. One way to write them down is to use the truth table. However, the truth table do not have the details of signal/state transition. The best way is to use a “State Diagram”. It is a diagram that tabulates the output states along with relevant inputs in a way that is much more expressive than the truth table.
The intention of this diagram is to show the present output states along with the next and the previous states. The inputs that would cause these states and transition of states are also clearly shown. While designing any complex digital systems, it is helpful to draw the state diagram before actually starting to designing the hardware. This way, the design can be completed with the least amount of effort. These diagrams are also used in designing state machines. State diagram & state machine are a big part of engineering that are related to digital electronics
Theory
A State diagram shows all the relevant states of output a digital system can come across. It also shows the inputs that can cause a certain state to transition to the next state. Systems with only finite numbers of output can be expressed with a state diagram. These diagrams are like a truth table but are a far more interactive as it shows the relevant states, the relevant inputs and the transition of states clearly. An important part of sequential circuit design is the generation of its state diagram.
Generally, the states are written in a circle and place in the diagram in a circle. Arrows are used to define transition of states. Relevant inputs are written on the side of the diagram to show this specific input causes transition of this state to the next. Input signal can be omitted if there is only one input e.g. a binary counter have only CLK input. Note that state diagram & state machine can be both synchronous or asynchronous. Generally, flip-flop is used in designing a large number of state machines. Therefore, a large number of state machines are synchronous.
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