Serial Interface 7135 to AVR microcontroller

//Timer2 is used to genrate  125khz pulse from pin 11 in uno and pin 5 is use to count pulse using Timer1

#include <avr/io.h>
#include <avr/interrupt.h>

const int pulseOut = 11;
const int LED_pin = 13;
const int BUSY_PIN = 2; //busy pin used as input counter @ pin5 and pin2
unsigned long ADC_count;

void setup() {
 
  Serial.begin(115200);//start Serial
 
  pinMode(11,OUTPUT);
  pinMode(LED_pin,OUTPUT);
  pinMode(BUSY_PIN,INPUT_PULLUP);

  attachInterrupt(digitalPinToInterrupt(BUSY_PIN),isr, CHANGE);//pin2 interrupt
 
//Timer2 used to generate 125kHz at pin 11

  TCCR2A |= (1<<COM2A0) | (1<<COM2B1) | (1<<WGM21) | (1<<WGM20);
  TCCR2B |= (1<<WGM22) | (1<<CS22);

// Timer1 used as counter @ pin5 and pin2 as input
  noInterrupts();
  TCCR1A = 0;
  TCCR1B = 0;
  TCNT1 = 0;
  //TCCR1B |= (1<<CS10);//clkI/O/1 (no prescaling)
  //TCCR1B |= (1<<CS10)|(1<<CS11) |(1<<CS12);//External clock source on T1 pin. Clock on rising edge.
  //TIMSK1 |= (1<<TOIE1);//enable time overflow
  interrupts();
}

void isr(){
  if (digitalRead(BUSY_PIN) == LOW) STARTtimer1();
  else STOPtimer1();
}

void STARTtimer1()
{
  //TCCR1B |= (1<<CS10)|(1<<CS11) |(1<<CS12);//External clock source on T1 pin. Clock on rising edge.
  TCCR1B |= (1<<CS10);//no prescaler
  ADC_count = TCNT1 - 10001;
}


void STOPtimer1()
{
  TCCR1A = 0;
  TCCR1B = 0;
  //Serial.println("STOP");
  TCNT1 = 0;
}

void loop() {
 
    Serial.println(ADC_count);   
 // Serial.println(TCNT1);
  delay (500) ;
 
}

#include <avr/io.h>
#include <avr/interrupt.h>

const int pulseOut = 11;
const int LED_pin = 13;
const int BUSY_PIN = 2; //busy pin used as input interrupt
const int BUSY_PIN_2 = 3; //busy pin used as input interrupt
volatile int ADC_count;

void setup() {
 
  Serial.begin(115200);//start Serial
 
  pinMode(11,OUTPUT);
  pinMode(LED_pin,OUTPUT);
  pinMode(BUSY_PIN,INPUT_PULLUP);
  pinMode(BUSY_PIN_2,INPUT_PULLUP);

  attachInterrupt(digitalPinToInterrupt(BUSY_PIN),STARTtimer1, FALLING);//pin2 interrupt
  attachInterrupt(digitalPinToInterrupt(BUSY_PIN_2),STOPtimer1, RISING);//pin3 interrupt
 
//Timer2 used to generate 125kHz at pin 11

  TCCR2A |= (1<<COM2A0) | (1<<COM2B1) | (1<<WGM21) | (1<<WGM20);
  TCCR2B |= (1<<WGM22) | (1<<CS22);

// Timer1 used as counter
  noInterrupts();
  TCCR1A = 0;
  TCCR1B = 0;
  TCNT1 = 0;
  interrupts();
}

void STARTtimer1()
{
  //TCCR1B |= (1<<CS10)|(1<<CS11) |(1<<CS12);//External clock source on T1 pin. Clock on rising edge.
  TCCR1B |= (1<<CS10);//no prescaler
   
}


void STOPtimer1()
{
  TCCR1A = 0;
  TCCR1B = 0;
  ADC_count = TCNT1 - 10001;
  TCNT1 = 0;
}

void loop() {
 
  Serial.println(ADC_count);  
  delay (1000) ;
   
}