Tutorial: Finite State Machine programming

Tutorial: Finite State Machine Programming

Introduction

We will learn how to design a logic with FSM and implement it in C-programming.

Example 1

Description

When the button is pressed, (input X=HIGH), Turn ON the LED.

Wait for 1 sec.

Button is released in the wait time.

When the button is pressed again, (input X=HIGH), Turn OFF the LED.

INPUT:

  • X: Button Pressed {0, 1}

OUTPUT:

  • LED {ON, OFF}

STATE:

  • S0: FAN OFF State

  • S1: FAN ON State

Moore FSM Table

Example Code: Moore FSM


#include <stdio.h>

// State definition
#define S0  0
#define S1  1

#define LOW  0
#define HIGH  1

unsigned char state = S0;
unsigned char nextstate = S0;
unsigned char input = LOW;
unsigned char ledOut = LOW;


typedef struct {
	unsigned int next[2];   // nextstate = FSM[state].next[input]
	unsigned int out;    // output = FSM[state].out
} State_t;

State_t FSM[2] = {
  {{S0, S1},LOW},
  {{S1, S0},HIGH}
};

int main()
{
    printf("Start\n\r");
    
    input=LOW;    
    nextstate = FSM[state].next[input];
    state=nextstate;
    ledOut = FSM[state].out;
    printf("state=%d,  ledOut=%d \n\r",state,ledOut);
    
    input=HIGH;
    nextstate = FSM[state].next[input];
    state=nextstate;
    ledOut = FSM[state].out;
    printf("state=%d,  ledOut=%d \n\r",state,ledOut);

    input=LOW;    
    nextstate = FSM[state].next[input];
    state=nextstate;
    ledOut = FSM[state].out;
    printf("state=%d,  ledOut=%d \n\r",state,ledOut);

    return 0;
}

Mealy FSM Table

Example Code: Mealy FSM

#include <stdio.h>

// State definition
#define S0  0
#define S1  1

#define LOW  0
#define HIGH  1

unsigned char state = S0;
unsigned char nextstate = S0;
unsigned char input = LOW;
unsigned char ledOut = LOW;


// State table definition
typedef struct {
	unsigned int next[2];       // nextstate = FSM[state].next[input]
	unsigned int out[2];        // output = FSM[state].out[input]
} State_t;

State_t FSM[2] = {
  { {S0, S1},{LOW,HIGH} },
  { {S1, S0},{HIGH,LOW} }
};

int main()
{
    printf("Start\n\r");
    
    input=LOW;
    ledOut = FSM[state].out[input];
    nextstate = FSM[state].next[input];
    state=nextstate;
    printf("state=%d,  ledOut=%d \n\r",state,ledOut);
    
    input=HIGH;
    ledOut = FSM[state].out[input];
    nextstate = FSM[state].next[input];
    state=nextstate;
    printf("state=%d,  ledOut=%d \n\r",state,ledOut);
    
    input=LOW;
    ledOut = FSM[state].out[input];
    nextstate = FSM[state].next[input];
    state=nextstate;
    printf("state=%d,  ledOut=%d \n\r",state,ledOut);
    
    return 0;
}

Example 2

Description

When the button is pressed, (input X=HIGH), Turn ON the LED and Turn ON the fan motor.

Wait for 1 sec.

Button is released in the wait time.

When the button is pressed again, (input X=HIGH), Turn OFF the LED and Turn OFF the fan motor.

Moore FSM Table

Example Code: Moore FSM

// State definition
#define S0  0
#define S1  1

// Address number of output in array
#define PWM 0
#define LED 1

typedef struct {
  uint32_t next[2];   // nextstate = FSM[state].next[input]
  uint32_t out[2];    // output = FSM[state].out[PWM or LED]
} State_t;

State_t FSM[2] = {
  {{S0, S1},{0   , LOW }},
  {{S1, S0},{160 , HIGH}}
};

const int ledPin = 13;
const int pwmPin = 11;
const int btnPin = 3;

unsigned char state = S0;
unsigned char input = 0;
unsigned char pwmOut = 0;
unsigned char ledOut = LOW;

void setup() {
  // initialize the LED pin as an output:
  pinMode(ledPin, OUTPUT);

  // Initialize pwm pin as an output:
  pinMode(pwmPin, OUTPUT);
  
  // initialize the pushbutton pin as an interrupt input:
  pinMode(btnPin, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(btnPin), pressed, FALLING);
  
  Serial.begin(9600);
}

void loop() {
  // First, Update next state. Then, Output.  Repeat
  // 1. Update State <-- Next State
  nextState();

  // 2. Output of states
  stateOutput();

  analogWrite(pwmPin, pwmOut);
  digitalWrite(ledPin, ledOut);

  delay(1000);
}

void pressed() {
  input = 1;
}

void nextState() {
  state = FSM[state].next[input];
  // Intialize Button Pressed 
  input = 0;
}

void stateOutput() {
  pwmOut = FSM[state].out[PWM];
  ledOut = FSM[state].out[LED];
}

Mealy FSM Table

Example Code: Mearly FSM

// State definition
#define S0  0
#define S1  1

// Address number of output in array
#define PWM 0
#define LED 1

const int ledPin = 13;
const int pwmPin = 11;
const int btnPin = 3;

unsigned char state = S0;
unsigned char nextstate = S0;
unsigned char input = 0;
unsigned char ledOut = LOW;
unsigned char pwmOut = 0;

// State table definition
typedef struct {
  uint32_t next[2];       // nextstate = FSM[state].next[input]
  uint32_t out[2][2];     // output = FSM[state].out[input][PWM or LED]
} State_t;

State_t FSM[2] = {
  { {S0, S1}, {{0  , LOW }, {160, HIGH}} },
  { {S1, S0}, {{160, HIGH}, {0  , LOW }} } 
};

void setup() {
  // initialize the LED pin as an output:
  pinMode(ledPin, OUTPUT);

  // Initialize pwm pin as an output:
  pinMode(pwmPin, OUTPUT);
  
  // initialize the pushbutton pin as an interrupt input:
  pinMode(btnPin, INPUT_PULLUP);
  attachInterrupt(digitalPinToInterrupt(btnPin), pressed, FALLING);
}

void loop() {
  // First, Output of current State. Then Update next state. Repeat

  // 1. Output State
  stateOutput();
  analogWrite(pwmPin, pwmOut);
  digitalWrite(ledPin, ledOut);

  // 2. Update State <-- Next State
  nextState();

  delay(1000);
}


void pressed() {
  input = 1;
}

void nextState() {
  nextstate = FSM[state].next[input];
  state = nextstate;

  // Intialize Button Pressed 
  input = 0;
}

void stateOutput() {
  pwmOut = FSM[state].out[input][PWM];
  ledOut = FSM[state].out[input][LED];
}
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