An ASM chart consists of three basic elements : The state box, the decision box, and the conditional box.

State box

: A state in the control sequence is indicated by a state box, as shown in the Fig, 8.1.2 As shown in the Fig. 8.1.2, rectangle shape is used to represent state box. At the left of this box is the name of the state, such as A, B, Qy, Qy- On the right hand top comer of the box is a list of the flip-flop values that define that state. The circuit outputs that can occur whenever the circuit is in the corresponding state regardless of input values are listed within the box. Finally, a line drawn from state box, known as exit, indicates the path to the next state

Decision box

The decision box describes the effect of an input on the control subsystem. It has a diamond shape box with two or more exit paths, as shown in the fig 8.1.3. The input condition to be tested is written inside the diamond box. Each value either 0 or 1 that may be assumed by an input or expression in a diamond is associated with an exit path from that diamond. These paths lead to the blocks corresponding to the next states of the circuit following the next clock pulse.

Conditional box

The state and decision boxes are familiar from use in conventional flowcharts. The third basic element, the conditional box, is unique to the ASM chart. It is an oval shape box. Its rounded corners differentiate it from the state box. The input path for the conditional box always comes from one of the exit paths of a decision box. The outputs that occur when the path to a conditional output box is satisfied are listed within the box.

Salient faetures:

1. An ASM chart describes the sequence of events as well as the timing relationship between the states of a sequential controller and the events that occur while going from one state to the next.
2. Every block in an ASM chart specifies the operations that are to be performed during one common clock pulse.
3. The operations specified within the state and conditional boxes in the block are performed in the datapath subsystem.
4. The change from one state to next is performed in the control subsystem. An ASM chart consists of one or more interconnected blocks.
5. An ASM block has one entrance and any number of exit paths represented by the structure of the decision boxes.
6. Each block in the ASM chart describes the state of the system during one clock-pulse interval. When a digital system enters the state associated with a given ASM block, the outputs indicated within the state box becomes true. The conditions associated with the decision boxes are evaluated to determine which path or paths to be followed to enter into the next ASM block.