Ressource documentaire: code example:

#include 
//adresses codées sur 7bits
//données
#define SLAVE_ADDR_8574_A 0x3e
//controle
#define SLAVE_ADDR_8574_B 0x3f
 
    //////////////////////////////////////////
    char readPort8574(char addr, char * ptr_value)
    /*addr, l'adresse du PCF8574
    ptr_value, pointeur pour renvoyer la valeur lue sur le port
    retourne -1 si échec 0 sinon*/
    {
        Wire.requestFrom((byte)addr, (byte)1);// demande la lecture d'1 octet depuis l'adresse du pérpiphérique
        if (Wire.available()==1) //si l'octet est disponible
        {
            (* ptr_value) = Wire.read(); // lire l'octet
            return 0;
        }
        else
        {
            (* ptr_value) =0; //valeur par défaut si le composant n'a pas acquité
            return -1;
        }
    }
    //////////////////////////////////////////
    char writePort8574(char addr, char value)
    /*addr, l'adresse du PCF8574
    value, la valeur à écrire sur le port
    retourne -1 si échec 0 sinon */
    {
        Wire.beginTransmission(addr);//démarre la transmission avec l'adresse du pérpiphérique
        Wire.write((byte)value);     //envoie la donnée
        if (Wire.endTransmission()==0)      //stoppe la transmission
            return 0;
        else
            return -1;
    }
    
    byte imageB;
   
//////////////////////////////////////////

bool sendCar(char c)
{
  char datab;
  //if busy return false;
   readPort8574(SLAVE_ADDR_8574_B,&datab);
  if ((datab & 2) ==2 )
  { 
   // Serial.println("occupée");
    return false;
  }
   writePort8574( SLAVE_ADDR_8574_A , c); 
   writePort8574( SLAVE_ADDR_8574_B , imageB&0xfe); //strobe à 0
   writePort8574( SLAVE_ADDR_8574_B , imageB|1); //strobe à 1
 
  
  return true;
}
//////////////////////////////////////////
void sendCarBlocking(char c){
   while (sendCar(c)==false);
}
//////////////////////////////////////////
void sendStringBlocking(char * ptrc){
   while ((*ptrc) !=0){
      while (sendCar(*ptrc)==false);
      ptrc++;
   }
}
char chaine[100]="PU1000,1000;PD1000,2000;PD2000,2000;PD2000,1000;PD1000,1000;";
char coord[10];
//////////////////////////////////////////
void traceCirclePointille(unsigned int cx,unsigned int cy,unsigned int r,unsigned int nbseg)
{
  
  unsigned int i=0;
  int x,y;
  float angle=0;
  float incangle=2*PI/nbseg;
  while (i<=nbseg){
    x=cx+r*cos(angle);
    y=cy+r*sin(angle);
 Serial.print(x);
 Serial.print(" , ");
 Serial.println(y);
 
 sendCarBlocking('P');
if ((i%2)==0) 
  sendCarBlocking('D');
else
  sendCarBlocking('U');

itoa(x,coord,10);
sendStringBlocking(coord);
sendCarBlocking(',');
itoa(y,coord,10);
sendStringBlocking(coord);
sendCarBlocking(';');
i++;
 angle=angle+incangle;
  }
}
//////////////////////////////////////////
void traceCircle(unsigned int cx,unsigned int cy,unsigned int r,unsigned int nbseg)
{
  
  unsigned int i=0;
  int x,y;
  float angle=0;
  float incangle=2*PI/nbseg;
  while (i<=nbseg){
    x=cx+r*cos(angle);
    y=cy+r*sin(angle);
 Serial.print(x);
 Serial.print(" , ");
 Serial.println(y);
 
 sendCarBlocking('P');
 sendCarBlocking('D');
itoa(x,coord,10);
sendStringBlocking(coord);
sendCarBlocking(',');
itoa(y,coord,10);
sendStringBlocking(coord);
sendCarBlocking(';');
i++;
 angle=angle+incangle;
  }

   sendCarBlocking('P');
 sendCarBlocking('U');
sendCarBlocking(',');
}
 
//////////////////////////////////////////
bool gotoyx(int16_t x,int16_t y,int16_t b)
{
 /*int16_t xmax=5000;
 int16_t ymax=5000;
 
 if (x<0) return -1;
 if (y<0) return -1;
 if (x>xmax) return -1;
 if (y>ymax) return -1;
 */
 sendCarBlocking('P');
if ((b%2)==0) 
  sendCarBlocking('D');
else
  sendCarBlocking('U');

itoa(x,coord,10);
sendStringBlocking(coord);
sendCarBlocking(',');
itoa(y,coord,10);
sendStringBlocking(coord);
sendCarBlocking(';');
  return 0;
}
//////////////////////////////////////////
void loop2()
{
static  int i=10;
  // Serial.print("JMB");
   Serial.println(i,HEX);
   delay(1000);
   i=i+1;
}
//////////////////////////////////////////
class Joystick{
private:
  int16_t x,y,b;
  int16_t minX,maxX,minY,maxY;
  int16_t xFactor,yFactor;
  int16_t centerX,centerY,dZ;
  uint8_t pinX,pinY,pinB;
public:
  Joystick(uint8_t pinXinit,uint8_t pinYinit,uint8_t pinBinit,int16_t dZinit) {
    pinX=pinXinit;
    pinY=pinYinit;
    pinB=pinBinit;
    dZ=dZinit; //dead Zone
    //par défaut les limites pour x et y sont les valeurs min et max codable
    minX=-32768;
    maxX=32767;
    minY=-32768;
    maxY=32767;
    xFactor=1;
    yFactor=1;
    }
  init(){ //analogRead ne fonctionne pas avant appel de setup()
    pinMode(pinB,INPUT_PULLUP); //pull up pour bouton
    x=0;
    y=0;
    b=!digitalRead(pinB);
    centerX= analogRead(pinX);
    centerY= analogRead(pinY);
  }
  setLimits(int16_t minXinit,int16_t maxXinit,int16_t minYinit,int16_t maxYinit){
    minX=minXinit;
    maxX=maxXinit;
    minY=minYinit;
    maxY=maxYinit;
  }
  setPos(int16_t xinit,int16_t yinit){
    x=xinit;
    y=yinit;
  }
  setPosCenter(){
    x=(maxX+minX)/2;
    y=(maxY+minY)/2;
  }
  setFactorOrientation(int16_t xFactorInit,int16_t yFactorInit){
    xFactor=xFactorInit;
    yFactor=yFactorInit;
  }
  
  update(){

    int16_t dX= (analogRead(pinX) - centerX)*xFactor;
    int16_t dY= (analogRead(pinY) - centerY)*yFactor;
    /*if (abs(dX)>dZ)
      x=x+dX;
    if (abs(dY)>dZ)
      y=y+dY;
      */
    if (dX>dZ)
      if (xminX-dX)
        x=x+dX;
      else
        x=minX;
    if (dY>dZ)
      if (yminY-dY)
        y=y+dY;
      else
        y=minY;        
        
    b=!digitalRead(pinB);
    /* Serial.print("centerX: ");
  Serial.print(centerX);
  Serial.print("centerY: ");
  Serial.println(centerY); 
  Serial.print("dX: ");
  Serial.print(dX);
  Serial.print("dY: ");
  Serial.println(dY);
  */
    }
  int16_t getX(){return x;}
  int16_t getY(){return y;}
  int16_t getB(){return b;}
  bool isUp(){return (y>centerY+dZ);}
  bool isDown(){return (ycenterX+dZ);}
  bool isRight(){return (x