Algorithmic State Machine ASM Charts

It is a sequential network which controls a digital system that carries out a step-by-step procedure or algorithm. Algorithmic State Machine is representation of a Finite State Machine suitable for FSMs with a larger number of inputs and outputs compared to FSMs expressed using state diagrams and state tables.

Elements used in ASM charts

State Box : Contains output list.

Decision Box : Condition is placed.

Conditional Output Box : Contains conditional output list.

ASM Block : contains one or more exit paths. Describes machine operation.

Development of ASM chart from state graph

There are two types of machines



MAELY MACHINE: Output is function of both input & present state

Steps for making ASM chart

i) Represent state by state boxes.

ii) After each box put input in each box.

iii) Depending on values of output the output in conditional box in paths where it will be “1”.

iv) Depending on values of input connect the path to next state box.

State Box represents a state.

Equivalent to a node in a state diagram or a row in a state table.

Contains register transfer actions or output signals

Moore-type outputs are listed inside of the box.

It is customary to write only the name of the signal that has to be asserted in the given state, e.g., z instead of z<=1.

Also, it might be useful to write an action to be taken, e.g., count <= count + 1, and only later translate it to asserting a control signal that causes a given action to take place (e.g., enable signal of a counter). State name Output signals or actions (Moore type)

Decision Box indicates that a given condition is to be tested and the exit path is to be chosen accordingly. The condition expression may include one or more inputs to the FSM.

Conditional Output Box denotes output signals that are of the Mealy type. The condition that determines whether such outputs are generated is specified in the decision box.

ASMs representing simple FSMs

Algorithmic state machines can model both Mealy and Moore Finite State Machines. They can also model machines that are of the mixed type.

Moore FSM State Diagram example

Control Unit Example Arbiter


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