I’m new on MDB communication and I’m working on a cashless payment device that communicate with the MDB protocol. I’m using, for know, an Arduino MEGA to communicate with this type of devices.
The problem that’s when I send a COMMAND like (RESET or Vend_Request) the device interact correctly (I mean with lights outputs) and with the application it’s all good and the request always has been approved on the application.
The problem that I can’t receive any thing on the serial like the POLL response form the device (like the ACK or something else) and I couldn’t find the problem to fix it.
There’s below a part form the code with the main functions in this problem:

void MDB_Setup() {
  // Set baud rate with setbaud.h
  UBRR0H = UBRRH_VALUE;
  UBRR0L = UBRRL_VALUE;
  // Disable USART rate doubler (arduino bootloader leaves it enabled...)
  UCSR0A &= ~(1 << U2X0);
  // Set 9600-9-N-1 UART mode
  UCSR0C = (0<<UMSEL01)|(0<<UMSEL00)|(0<<UPM01)|(0<<UPM00)|(0<<USBS0)|(1<<UCSZ01)|(1<<UCSZ00);
  UCSR0B |= (1<<UCSZ02); // 9bit
  // Enable rx/tx
  UCSR0B |= (1<<RXEN0)|(1<<TXEN0);
}


//Poll FUNCTION:
void PollDevice(byte devaddrbyte){
  struct MDB_Byte addrbyte;
  coin_read_value=true;
  rcvcomplete = 0;
  int addrtx = 0;
  addrbyte.data = devaddrbyte;
  addrbyte.mode = 0x01;
  memcpy(&addrtx, &addrbyte, 2);
  MDB_write(addrtx);
  MDB_write(addrbyte.data);
  processresponse(addrbyte.data & ADDRESS_MASK);
  coin_read_value=false;
}

// Process response 
void processresponse(int addr){
  mdboverflow = 0;
  rcvcomplete = 0;
  while (!rcvcomplete){
    MDB_read();
  }
  if ((rcvcomplete) && (!mdboverflow)){
    if (MDB_BUFFER_COUNT > 1){
      MDB_write(0x00); // Enviar ACK al dispositivo MDB si la respuesta periférica no es solo un *ACK*, de lo contrario, el periférico intentará enviar datos no confirmados con los próximos comandos de "poll"
      Serial.print("ACK Sent");
    } else {
      if (MDB_BUFFER_COUNT == 1){
        // Solo se recibió un *ACK* del dispositivo periférico, no se necesita confirmación
        Serial.print("ACK");
      }
    }
  }
  for(uint8_t i = 0; i < MDB_BUFFER_COUNT; i++) // Corrección aquí
  {
    Serial.print("Response Data: ");
    Serial.println(MDB_BUFFER[i].data, HEX);
  }
  Serial.println();
}

// MDB Send function
void MDB_Send(byte UART_BUFFER[37],int UART_BUFFER_COUNT){
  //command seems valid, let's try to send it to peripheral
  struct MDB_Byte AddressByte;
  int addrtx = 0;
  AddressByte.data = UART_BUFFER[0];
  AddressByte.mode = 0x01;
  memcpy(&addrtx, &AddressByte, 2);
  MDB_write(addrtx);
  for (int i = 1; i < UART_BUFFER_COUNT; i++){
    MDB_write(UART_BUFFER[i]);
  }
  processresponse(UART_BUFFER[0] & ADDRESS_MASK);
}

void MDB_write(int data) {
  struct MDB_Byte b;
  memcpy(&b, &data, 2);
  write_9bit(b);
}

int MDB_Receive() {
  unsigned char resh, resl;
  char tmpstr[64];
  int rtr = 0;
  // Wait for data to be received
  while ((!(UCSR0A & (1<<RXC0))) and rtr < 50) {
    delay(1);
    rtr++;
  }
  if (rtr == 50){
    mdboverflow = 1;
    rcvcomplete = 1;
  }
  // Get 9th bit, then data from buffer
  resh = UCSR0B;
  resl = UDR0;
  // Filter the 9th bit, then return only data wo mode bit
  resh = (resh >> 1) & 0x01;
  return ((resh << 8) | resl);
}


void MDB_getByte(struct MDB_Byte* mdbb) {
  int b;
  b = 0;
  b = MDB_Receive();
  memcpy (mdbb, &b, 2);  
}

byte MDB_ChecksumValidate() {
  int sum = 0;
  for (int i=0; i < (MDB_BUFFER_COUNT-1); i++)
    sum += MDB_BUFFER[i].data;
  if (MDB_BUFFER[MDB_BUFFER_COUNT-1].data == (sum & 0xFF))
    return 1;
  else
    return 0;
}


// Cashless loop 
void Cashless_Device()
{
  if (millis() - temp_poll > 150)
  {
    temp_poll = millis();
    PollDevice(0x12);
    MDBFlush();
  }
}

And thank you in advence.

I’m tring to get the poll request or the poll response but nothing