Maintaining Variable Values in Finite State Machines

Finite State Machines (FSMs) are a fundamental concept in computer science, used to model systems with a limited number of states. They are widely used in software and hardware design, and are especially useful in embedded systems. In this article, we will discuss how to maintain variable values in FSMs, which is an important aspect of designing and implementing FSMs in real-world applications.

What is a Finite State Machine?

A Finite State Machine is a mathematical model of a system that can be in one of a finite number of states at any given time. The system transitions from one state to another based on inputs it receives. Each transition is associated with a set of actions that are executed when the transition occurs. FSMs are used to model systems that are reactive, meaning that they respond to inputs in a predictable way.

Variables in Finite State Machines

Variables are used in FSMs to store information about the system's state and inputs. Variables can be used to store data that is needed across multiple states or inputs. For example, a variable can be used to store a counter that is incremented each time a particular input is received. Variables can also be used to store data that is needed to make decisions about which state to transition to next.

Maintaining Variable Values

Maintaining variable values in FSMs is an important aspect of designing and implementing FSMs in real-world applications. The value of a variable must be preserved across transitions, so that it can be used in the next state. There are two ways to maintain variable values in FSMs: using a variable table or using a variable stack.

Using a Variable Table

A variable table is a data structure that is used to store the values of variables in an FSM. Each row in the table corresponds to a state in the FSM, and each column corresponds to a variable. The value of each variable is stored in the corresponding cell in the table. When the FSM transitions from one state to another, the values of the variables are copied from the old state to the new state. This ensures that the values of the variables are preserved across transitions.

State 1   State 2   State 3
Var1      Var1      Var1
Var2      Var2      Var2
Var3      Var3      Var3

In the above example, the variable table has three columns, one for each state in the FSM. The values of variables Var1, Var2, and Var3 are preserved across transitions from one state to another.

Using a Variable Stack

A variable stack is a data structure that is used to store the values of variables in an FSM. Each time a variable is assigned a new value, the old value is pushed onto the stack. When the FSM transitions from one state to another, the values of the variables are popped from the stack and assigned to the variables in the new state. This ensures that the values of the variables are preserved across transitions.

State 1   State 2   State 3
Push Var1  Pop Var1  Pop Var1
Push Var2  Pop Var2  Pop Var2
Push Var3  Pop Var3  Pop Var3

In the above example, the variable stack has three entries, one for each state in the FSM. The values of variables Var1, Var2, and Var3 are pushed onto the stack when they are assigned new values. When the FSM transitions from one state to another, the values of the variables are popped from the stack and assigned to the variables in the new state.

Maintaining variable values in Finite State Machines is an important aspect of designing and implementing FSMs in real-world applications. Variable tables and variable stacks are two ways to maintain variable values in FSMs. By using a variable table or a variable stack, the values of variables can be preserved across transitions, which is essential for the correct functioning of FSMs.

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