NHD-0420DZ-NSW-BBW don't display any character

I have a NHD-0420DZ-NSW-BBW connected to an arduino to test it. I am using 4bit connection. Wirings are:

D0 = 0;   // B4
D1 = 0;   // B5
D2 = 0;   // B6
D3 = 0;   // B7

D5 = 0;   // pin E
D6 = 0;   // pin R/W low=w, high=read
D7 = 0;   // RS  low=instruction, high=data

D9=0;     // Contrast

I have used the sample code from newhaven site:

https://www.newhavendisplay.com/resources_dataFiles/excode/txt/CharLCD/4bit_character.txt

And this is the 'translated' code for arduino uno:

/*
 D0 = 0;   // B4
 D1 = 0;   // B5
 D2 = 0;   // B6
 D3 = 0;   // B7

 D5 = 0;   // pin E
 D6 = 0;   // pin R/W low=w, high=read
 D7 = 0;   // RS  low=instruction, high=data

 D9=0;     // Contrasto
*/

int _EN = 5;
int _RW = 6;
int _RS = 7;

int _contrast = 9;

int _B4 = 0;
int _B5 = 1;
int _B6 = 2;
int _B7 = 3;

void setup() {
  // put your setup code here, to run once:
  pinMode(_B4, OUTPUT);
  pinMode(_B5, OUTPUT);
  pinMode(_B6, OUTPUT);
  pinMode(_B7, OUTPUT);

  pinMode(_EN, OUTPUT);  // pin E
  pinMode(_RW, OUTPUT);  // pin R/W low=w, high=r
  pinMode(_RS, OUTPUT);  // pin RS

  Serial.begin(9600);

  start();

  Serial.println("clear display and home");
  command(0x01);

  Serial.println("Writing Hello");
  Write('H'); Write('e'); Write('l'); Write('l'); Write('o');

  analogWrite(_contrast, 127);  // set contrast to half course
}

void loop() {
  //Serial.println("ingresso loop");
  delay(100);
}

void WriteData(char i) {
  digitalWrite(_B4, ((i & 0x10) != 0) ? HIGH : LOW);
  digitalWrite(_B5, ((i & 0x20) != 0) ? HIGH : LOW);
  digitalWrite(_B6, ((i & 0x40) != 0) ? HIGH : LOW);
  digitalWrite(_B7, ((i & 0x80) != 0) ? HIGH : LOW);
}

/**********************************************************/
void command(char i)
{
  WriteData(i);       //put data on output Port
  digitalWrite(_RS, LOW); //D_I = 0;    //D/I=LOW : send instruction
  digitalWrite(_RW, LOW);  //R_W = 0;    //R/W=LOW : Write
  Nybble();   //Send upper 4 bits
  i = i << 4; //Shift over by 4 bits
  WriteData(i);
  Nybble();   //Send upper 4 bits
}
/**********************************************************/
void Write(char i)
{
  WriteData(i);        //put data on output Port
  digitalWrite(_RS, HIGH);  //D_I = 1;  //D/I=HIGH : send data
  digitalWrite(_RW, LOW);  //R_W = 0;  //R/W=LOW : Write
  Nybble(); //Clock upper 4 bits
  i = i << 4; //Shift over by 4 bits
  WriteData(i);   //put data on output Port
  Nybble(); //Clock upper 4 bits
}
/**********************************************************/
void Nybble()
{
  digitalWrite(_EN, HIGH); // E = 1;
  delay(10); //enable pulse width >= 300ns
  digitalWrite(_EN, LOW); // E = 0;    Clock enable: falling edge
  delay(10); //enable pulse width >= 300ns
}
/**********************************************************/
void start()
{
  WriteData(0);
  Serial.println("Inizializzazione...");
  digitalWrite(_RS, LOW); //D_I = 0;    //D/I=LOW : send instruction
  digitalWrite(_RW, LOW);  //R_W = 0;    //R/W=LOW : Write
  digitalWrite(_EN, LOW);
  Serial.println("watinig 1 sec");
  delay(1000);    //Wait >40 msec after power is applied
  WriteData(0x30);     //put 0x30 on the output port
  delay(30);     //must wait 5ms, busy flag not available
  Nybble();      //command 0x30 = Wake up
  delay(10);     //must wait 160us, busy flag not available
  Nybble();      //command 0x30 = Wake up #2
  delay(10);     //must wait 160us, busy flag not available
  Nybble();      //command 0x30 = Wake up #3
  delay(10);     //can check busy flag now instead of delay
  WriteData(0x20);     //put 0x20 on the output port
  Nybble();      //Function set: 4-bit interface
  Serial.println("functionset 4bit/4linee");
  command(0x28); //Function set: 4-bit/4-line
  Serial.println("display on and blinking cursor");
  command(0x08); //Display ON; Blinking cursor
  Serial.println("cursor shift");
  command(0x14); //Set cursor
  Serial.println("entry mode set");
  command(0x06); //Entry Mode set
}