PCF8574 mit Taster auslesen

[HaWe]

ich veerwende diesen Code für Arduino C/C++:

#include <Wire.h>

#define ADDR_PCF8574  0x30

void setup() {
   Wire.begin();
   writei2cbyte(ADDR_PCF8574, 0xff);
   //...
}

void writei2cbyte(int addr, byte data) {
  Wire.beginTransmission(addr);
  Wire.write(data);
  Wire.endTransmission();
  delay(5);
}

uint8_t readi2cbyte(uint8_t addr, uint8_t reg) {
  uint8_t  bdata;

  Wire.beginTransmission(addr);
  Wire.write(reg);                   // target data register number
  Wire.endTransmission();

  Wire.requestFrom(addr, reg);           // Request 1 bytes from PCF8574
  while(Wire.available() < 1);           // Wait for byte to become available
  bdata = Wire.read();      
  return(bdata);
}

  //...
  uint8_t bitmask = readi2cbyte(ADDR_PCF8574, 1);  // read all btn states (bitmask) at reg 1
  if(bitRead(bitmask,1) {...}
  else 
  if(bitRead(bitmask,2) {...}  
  //...