Problem about using PCF8574 as an input without PCF8574 library.

Projects Networking, Protocols, and Devices
1

Hello, I'm trying to learn about TWI inteface with PCF8574 and testing on Proteus. I want to use 1 PCF8574 as read button status and show it onto 3 pieces 7 segment digits which are connected to 3 pieces PCF8574. My problem is when I press a button then it does not show any result or sometimes show strange values. What can be problem ?
My code and schematic is attached to the message.

#include <Wire.h>
#define ones_pcf8574_addr 0b0100000 
#define tens_pcf8574_addr 0b0100001 
#define hundreds_pcf8574_addr 0b0100010 
#define button_pcf8574_addr 0b0100100

byte seg[10] = {
              0b01111110, 0b00110000, 0b01101101, 0b01111001, 0b00110011, 0b01011011,
              
              0b01011111, 0b01110000, 0b01111111, 0b01111011
          };
volatile byte _data = 0xff;
boolean hasInt;
byte value = 0;

void extInt() {
  hasInt = true;
  value++;
}

void setup() {
  Wire.begin();
  pinMode(8, INPUT);
  pinMode(9, OUTPUT);
  ones(0);
  tens(0);
  hundreds(0);
  attachInterrupt(0, extInt, FALLING);
}

void loop() {
  if(hasInt) {
    readData();
    hasInt = false;
  }
}

void readData() {
  //byte _data;
  Wire.requestFrom(button_pcf8574_addr, 1);
  if (Wire.available()) {
    _data = Wire.read();
  }
  display(_data);
}

void ones(byte val) {
  Wire.beginTransmission(ones_pcf8574_addr);
  Wire.write(seg[val]);
  Wire.endTransmission();
  delay(5);
}

void tens(byte val) {
  Wire.beginTransmission(tens_pcf8574_addr);
  Wire.write(seg[val]);
  Wire.endTransmission();
  delay(5);
}

void hundreds(byte val) {
  Wire.beginTransmission(hundreds_pcf8574_addr);
  Wire.write(seg[val]);
  Wire.endTransmission();
  delay(5);
}

void display(byte val) {
  ones(val % 10);
  tens(val / 10);
  hundreds(val / 100);
}

PCF8574.jpg
PCF8574.jpg1121×601 108 KB

2

One of my problem was wrong display function, so corrected version is;

void display(byte val) {
  int _hundreds = val / 100; // 241 / 100 = 2
  int _tens = (val - (_hundreds * 100)) / 10; //241 - (2 * 100) = 41 / 10 = 4
  int _ones = val % 10;
  ones(_ones);
  tens(_tens);
  hundreds(_hundreds);
}

in that way, I can see PCF8574's input register values such as 254,253,251,247,239. But when I release the button then I see 255 value on display. How can I reset value to "000" ? is this about external interrupt settings ?