# 18.5 State Tables – Pulse and Digital Circuits

##### 18.5 STATE TABLES

The state table representation of a sequential circuit consists of three sections, labelled as the present state, next state and the output. The present state designates the state of flip-flops before the occurrence of a clock pulse. The next state shows the state of flip-flops after the clock pulse, and the output section lists the value of the output variables during the present state.

#### 18.5.1 State Diagrams

In addition to the graphical symbols, tables or equations, counter can also be represented pictorially by a state diagram. In this diagram, a state is represented by a circle, and the transition between the states is indicated by directed lines (or arcs) connecting the circles. An example of a state diagram is shown in Fig. 18.24.

The binary number inside each circle identifies the state of the counter. The directed lines are labelled with two binary numbers separated by a slash (/). The input value that causes the state transition is labelled first. The number after the slash symbol / gives the value of the output. For example, the directed line from state 00 to 01 is labelled as 1/0, meaning that, if the sequential circuit is in a present state and the input is 1, then the next state is 01 and the output is 0. If it is in a present state 00 and the input is 0, it will remain in that state. A directed line connecting a circle with itself indicates that no change of state occurs. The state diagram provides exactly the same information as the state table and is obtained directly from the state table.