text: /**************************************************************************/
  /*!
      @file     Adafruit_PN532.cpp
      @author   Adafruit Industries
      @license  BSD (see license.txt)
  
  	  Driver for NXP's PN532 NFC/13.56MHz RFID Transceiver
  
  	  This is a library for the Adafruit PN532 NFC/RFID breakout boards
  	  This library works with the Adafruit NFC breakout
  	  ----> https://www.adafruit.com/products/364
  
  	  Check out the links above for our tutorials and wiring diagrams
  	  These chips use SPI or I2C to communicate.
  
  	  Adafruit invests time and resources providing this open source code,
  	  please support Adafruit and open-source hardware by purchasing
  	  products from Adafruit!
  
      @section  HISTORY
  
      v2.1 - Added NTAG2xx helper functions
  
      v2.0 - Refactored to add I2C support from Adafruit_NFCShield_I2C library.
  
      v1.4 - Added setPassiveActivationRetries()
  
      v1.2 - Added writeGPIO()
           - Added readGPIO()
  
      v1.1 - Changed readPassiveTargetID() to handle multiple UID sizes
           - Added the following helper functions for text display
               static void PrintHex(const byte * data, const uint32_t numBytes)
               static void PrintHexChar(const byte * pbtData, const uint32_t numBytes)
           - Added the following Mifare Classic functions:
               bool mifareclassic_IsFirstBlock (uint32_t uiBlock)
               bool mifareclassic_IsTrailerBlock (uint32_t uiBlock)
               uint8_t mifareclassic_AuthenticateBlock (uint8_t * uid, uint8_t uidLen, uint32_t blockNumber, uint8_t keyNumber, uint8_t * keyData)
               uint8_t mifareclassic_ReadDataBlock (uint8_t blockNumber, uint8_t * data)
               uint8_t mifareclassic_WriteDataBlock (uint8_t blockNumber, uint8_t * data)
           - Added the following Mifare Ultalight functions:
               uint8_t mifareultralight_ReadPage (uint8_t page, uint8_t * buffer)
  */
  /**************************************************************************/
  #if ARDUINO >= 100
   #include "Arduino.h"
  #else
   #include "WProgram.h"
  #endif
  
  #include <Wire.h>
  #if defined(__AVR__) || defined(__i386__) || defined(ARDUINO_ARCH_SAMD) || defined(ESP8266) || defined(ARDUINO_ARCH_STM32)
   #define WIRE Wire
  #else // Arduino Due
   #define WIRE Wire1
  #endif
  
  #include <SPI.h>
  
  #include "Adafruit_PN532.h"
  
  byte pn532ack[] = {0x00, 0x00, 0xFF, 0x00, 0xFF, 0x00};
  byte pn532response_firmwarevers[] = {0x00, 0xFF, 0x06, 0xFA, 0xD5, 0x03};
  
  // Uncomment these lines to enable debug output for PN532(SPI) and/or MIFARE related code
  // #define PN532DEBUG
  // #define MIFAREDEBUG
  
  // If using Native Port on Arduino Zero or Due define as SerialUSB
  #define PN532DEBUGPRINT Serial
  //#define PN532DEBUGPRINT SerialUSB
  
  // Hardware SPI-specific configuration:
  #ifdef SPI_HAS_TRANSACTION
      #define PN532_SPI_SETTING SPISettings(1000000, LSBFIRST, SPI_MODE0)
  #else
      #define PN532_SPI_CLOCKDIV SPI_CLOCK_DIV16
  #endif
  
  #define PN532_PACKBUFFSIZ 255
  byte pn532_packetbuffer[PN532_PACKBUFFSIZ];
  
  #ifndef _BV
      #define _BV(bit) (1<<(bit))
  #endif
  
  /**************************************************************************/
  /*!
      @brief  Sends a single byte via I2C
  
      @param  x    The byte to send
  */
  /**************************************************************************/
  static inline void i2c_send(uint8_t x)
  {
    #if ARDUINO >= 100
      WIRE.write((uint8_t)x);
    #else
      WIRE.send(x);
    #endif
  }
  
  /**************************************************************************/
  /*!
      @brief  Reads a single byte via I2C
  */
  /**************************************************************************/
  static inline uint8_t i2c_recv(void)
  {
    #if ARDUINO >= 100
      return WIRE.read();
    #else
      return WIRE.receive();
    #endif
  }
  
  /**************************************************************************/
  /*!
      @brief  Instantiates a new PN532 class using software SPI.
  
      @param  clk       SPI clock pin (SCK)
      @param  miso      SPI MISO pin
      @param  mosi      SPI MOSI pin
      @param  ss        SPI chip select pin (CS/SSEL)
  */
  /**************************************************************************/
  Adafruit_PN532::Adafruit_PN532(uint8_t clk, uint8_t miso, uint8_t mosi, uint8_t ss):
    _clk(clk),
    _miso(miso),
    _mosi(mosi),
    _ss(ss),
    _irq(0),
    _reset(0),
    _usingSPI(true),
    _hardwareSPI(false)
  {
    pinMode(_ss, OUTPUT);
    pinMode(_clk, OUTPUT);
    pinMode(_mosi, OUTPUT);
    pinMode(_miso, INPUT);
  }
  
  /**************************************************************************/
  /*!
      @brief  Instantiates a new PN532 class using I2C.
  
      @param  irq       Location of the IRQ pin
      @param  reset     Location of the RSTPD_N pin
  */
  /**************************************************************************/
  Adafruit_PN532::Adafruit_PN532(uint8_t irq, uint8_t reset):
    _clk(0),
    _miso(0),
    _mosi(0),
    _ss(0),
    _irq(irq),
    _reset(reset),
    _usingSPI(false),
    _hardwareSPI(false)
  {
    pinMode(_irq, INPUT);
    pinMode(_reset, OUTPUT);
  }
  
  /**************************************************************************/
  /*!
      @brief  Instantiates a new PN532 class using hardware SPI.
  
      @param  ss        SPI chip select pin (CS/SSEL)
  */
  /**************************************************************************/
  Adafruit_PN532::Adafruit_PN532(uint8_t ss):
    _clk(0),
    _miso(0),
    _mosi(0),
    _ss(ss),
    _irq(0),
    _reset(0),
    _usingSPI(true),
    _hardwareSPI(true)
  {
    pinMode(_ss, OUTPUT);
  }
  
  /**************************************************************************/
  /*!
      @brief  Setups the HW
  */
  /**************************************************************************/
  void Adafruit_PN532::begin() {
    if (_usingSPI) {
      // SPI initialization
      if (_hardwareSPI) {
        SPI.begin();
  
        #ifdef SPI_HAS_TRANSACTION
          SPI.beginTransaction(PN532_SPI_SETTING);
        #else
          SPI.setDataMode(SPI_MODE0);
          SPI.setBitOrder(LSBFIRST);
          SPI.setClockDivider(PN532_SPI_CLOCKDIV);
        #endif
      }
      digitalWrite(_ss, LOW);
  
      delay(1000);
  
      // not exactly sure why but we have to send a dummy command to get synced up
      pn532_packetbuffer[0] = PN532_COMMAND_GETFIRMWAREVERSION;
      sendCommandCheckAck(pn532_packetbuffer, 1);
  
      // ignore response!
  
      digitalWrite(_ss, HIGH);
      #ifdef SPI_HAS_TRANSACTION
        if (_hardwareSPI) SPI.endTransaction();
      #endif
    }
    else {
      // I2C initialization.
      WIRE.begin();
  
      // Reset the PN532
      digitalWrite(_reset, HIGH);
      digitalWrite(_reset, LOW);
      delay(400);
      digitalWrite(_reset, HIGH);
      delay(10);  // Small delay required before taking other actions after reset.
                  // See timing diagram on page 209 of the datasheet, section 12.23.
    }
  }
  
  /**************************************************************************/
  /*!
      @brief  Prints a hexadecimal value in plain characters
  
      @param  data      Pointer to the byte data
      @param  numBytes  Data length in bytes
  */
  /**************************************************************************/
  void Adafruit_PN532::PrintHex(const byte * data, const uint32_t numBytes)
  {
    uint32_t szPos;
    for (szPos=0; szPos < numBytes; szPos++)
    {
      PN532DEBUGPRINT.print(F("0x"));
      // Append leading 0 for small values
      if (data[szPos] <= 0xF)
        PN532DEBUGPRINT.print(F("0"));
      PN532DEBUGPRINT.print(data[szPos]&0xff, HEX);
      if ((numBytes > 1) && (szPos != numBytes - 1))
      {
        PN532DEBUGPRINT.print(F(" "));
      }
    }
    PN532DEBUGPRINT.println();
  }
  
  /**************************************************************************/
  /*!
      @brief  Prints a hexadecimal value in plain characters, along with
              the char equivalents in the following format
  
              00 00 00 00 00 00  ......
  
      @param  data      Pointer to the byte data
      @param  numBytes  Data length in bytes
  */
  /**************************************************************************/
  void Adafruit_PN532::PrintHexChar(const byte * data, const uint32_t numBytes)
  {
    uint32_t szPos;
    for (szPos=0; szPos < numBytes; szPos++)
    {
      // Append leading 0 for small values
      if (data[szPos] <= 0xF)
        PN532DEBUGPRINT.print(F("0"));
      PN532DEBUGPRINT.print(data[szPos], HEX);
      if ((numBytes > 1) && (szPos != numBytes - 1))
      {
        PN532DEBUGPRINT.print(F(" "));
      }
    }
    PN532DEBUGPRINT.print(F("  "));
    for (szPos=0; szPos < numBytes; szPos++)
    {
      if (data[szPos] <= 0x1F)
        PN532DEBUGPRINT.print(F("."));
      else
        PN532DEBUGPRINT.print((char)data[szPos]);
    }
    PN532DEBUGPRINT.println();
  }
  
  /**************************************************************************/
  /*!
      @brief  Checks the firmware version of the PN5xx chip
  
      @returns  The chip's firmware version and ID
  */
  /**************************************************************************/
  uint32_t Adafruit_PN532::getFirmwareVersion(void) {
    uint32_t response;
  
    pn532_packetbuffer[0] = PN532_COMMAND_GETFIRMWAREVERSION;
  
    if (! sendCommandCheckAck(pn532_packetbuffer, 1)) {
      return 0;
    }
  
    // read data packet
    readdata(pn532_packetbuffer, 12);
  
    // check some basic stuff
    if (0 != strncmp((char *)pn532_packetbuffer, (char *)pn532response_firmwarevers, 6)) {
  #ifdef PN532DEBUG
        PN532DEBUGPRINT.println(F("Firmware doesn't match!"));
  #endif
      return 0;
    }
  
    int offset = _usingSPI ? 6 : 7;  // Skip a response byte when using I2C to ignore extra data.
    response = pn532_packetbuffer[offset++];
    response <<= 8;
    response |= pn532_packetbuffer[offset++];
    response <<= 8;
    response |= pn532_packetbuffer[offset++];
    response <<= 8;
    response |= pn532_packetbuffer[offset++];
  
    return response;
  }
  
  
  /**************************************************************************/
  /*!
      @brief  Sends a command and waits a specified period for the ACK
  
      @param  cmd       Pointer to the command buffer
      @param  cmdlen    The size of the command in bytes
      @param  timeout   timeout before giving up
  
      @returns  1 if everything is OK, 0 if timeout occured before an
                ACK was recieved
  */
  /**************************************************************************/
  // default timeout of one second
  bool Adafruit_PN532::sendCommandCheckAck(uint8_t *cmd, uint8_t cmdlen, uint16_t timeout) {
    uint16_t timer = 0;
  
    // write the command
    writecommand(cmd, cmdlen);
  
    // Wait for chip to say its ready!
    if (!waitready(timeout)) {
      return false;
    }
  
    #ifdef PN532DEBUG
      if (!_usingSPI) {
        PN532DEBUGPRINT.println(F("IRQ received"));
      }
    #endif
  
    // read acknowledgement
    if (!readack()) {
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.println(F("No ACK frame received!"));
      #endif
      return false;
    }
  
    // For SPI only wait for the chip to be ready again.
    // This is unnecessary with I2C.
    if (_usingSPI) {
      if (!waitready(timeout)) {
        return false;
      }
    }
  
    return true; // ack'd command
  }
  
  /**************************************************************************/
  /*!
      Writes an 8-bit value that sets the state of the PN532's GPIO pins
  
      @warning This function is provided exclusively for board testing and
               is dangerous since it will throw an error if any pin other
               than the ones marked "Can be used as GPIO" are modified!  All
               pins that can not be used as GPIO should ALWAYS be left high
               (value = 1) or the system will become unstable and a HW reset
               will be required to recover the PN532.
  
               pinState[0]  = P30     Can be used as GPIO
               pinState[1]  = P31     Can be used as GPIO
               pinState[2]  = P32     *** RESERVED (Must be 1!) ***
               pinState[3]  = P33     Can be used as GPIO
               pinState[4]  = P34     *** RESERVED (Must be 1!) ***
               pinState[5]  = P35     Can be used as GPIO
  
      @returns 1 if everything executed properly, 0 for an error
  */
  /**************************************************************************/
  bool Adafruit_PN532::writeGPIO(uint8_t pinstate) {
    uint8_t errorbit;
  
    // Make sure pinstate does not try to toggle P32 or P34
    pinstate |= (1 << PN532_GPIO_P32) | (1 << PN532_GPIO_P34);
  
    // Fill command buffer
    pn532_packetbuffer[0] = PN532_COMMAND_WRITEGPIO;
    pn532_packetbuffer[1] = PN532_GPIO_VALIDATIONBIT | pinstate;  // P3 Pins
    pn532_packetbuffer[2] = 0x00;    // P7 GPIO Pins (not used ... taken by SPI)
  
    #ifdef PN532DEBUG
      PN532DEBUGPRINT.print(F("Writing P3 GPIO: ")); PN532DEBUGPRINT.println(pn532_packetbuffer[1], HEX);
    #endif
  
    // Send the WRITEGPIO command (0x0E)
    if (! sendCommandCheckAck(pn532_packetbuffer, 3))
      return 0x0;
  
    // Read response packet (00 FF PLEN PLENCHECKSUM D5 CMD+1(0x0F) DATACHECKSUM 00)
    readdata(pn532_packetbuffer, 8);
  
    #ifdef PN532DEBUG
      PN532DEBUGPRINT.print(F("Received: "));
      PrintHex(pn532_packetbuffer, 8);
      PN532DEBUGPRINT.println();
    #endif
  
    int offset = _usingSPI ? 5 : 6;
    return  (pn532_packetbuffer[offset] == 0x0F);
  }
  
  /**************************************************************************/
  /*!
      Reads the state of the PN532's GPIO pins
  
      @returns An 8-bit value containing the pin state where:
  
               pinState[0]  = P30
               pinState[1]  = P31
               pinState[2]  = P32
               pinState[3]  = P33
               pinState[4]  = P34
               pinState[5]  = P35
  */
  /**************************************************************************/
  uint8_t Adafruit_PN532::readGPIO(void) {
    pn532_packetbuffer[0] = PN532_COMMAND_READGPIO;
  
    // Send the READGPIO command (0x0C)
    if (! sendCommandCheckAck(pn532_packetbuffer, 1))
      return 0x0;
  
    // Read response packet (00 FF PLEN PLENCHECKSUM D5 CMD+1(0x0D) P3 P7 IO1 DATACHECKSUM 00)
    readdata(pn532_packetbuffer, 11);
  
    /* READGPIO response should be in the following format:
  
      byte            Description
      -------------   ------------------------------------------
      b0..5           Frame header and preamble (with I2C there is an extra 0x00)
      b6              P3 GPIO Pins
      b7              P7 GPIO Pins (not used ... taken by SPI)
      b8              Interface Mode Pins (not used ... bus select pins)
      b9..10          checksum */
  
    int p3offset = _usingSPI ? 6 : 7;
  
    #ifdef PN532DEBUG
      PN532DEBUGPRINT.print(F("Received: "));
      PrintHex(pn532_packetbuffer, 11);
      PN532DEBUGPRINT.println();
      PN532DEBUGPRINT.print(F("P3 GPIO: 0x")); PN532DEBUGPRINT.println(pn532_packetbuffer[p3offset],   HEX);
      PN532DEBUGPRINT.print(F("P7 GPIO: 0x")); PN532DEBUGPRINT.println(pn532_packetbuffer[p3offset+1], HEX);
      PN532DEBUGPRINT.print(F("IO GPIO: 0x")); PN532DEBUGPRINT.println(pn532_packetbuffer[p3offset+2], HEX);
      // Note: You can use the IO GPIO value to detect the serial bus being used
      switch(pn532_packetbuffer[p3offset+2])
      {
        case 0x00:    // Using UART
          PN532DEBUGPRINT.println(F("Using UART (IO = 0x00)"));
          break;
        case 0x01:    // Using I2C
          PN532DEBUGPRINT.println(F("Using I2C (IO = 0x01)"));
          break;
        case 0x02:    // Using SPI
          PN532DEBUGPRINT.println(F("Using SPI (IO = 0x02)"));
          break;
      }
    #endif
  
    return pn532_packetbuffer[p3offset];
  }
  
  /**************************************************************************/
  /*!
      @brief  Configures the SAM (Secure Access Module)
  */
  /**************************************************************************/
  bool Adafruit_PN532::SAMConfig(void) {
    pn532_packetbuffer[0] = PN532_COMMAND_SAMCONFIGURATION;
    pn532_packetbuffer[1] = 0x01; // normal mode;
    pn532_packetbuffer[2] = 0x14; // timeout 50ms * 20 = 1 second
    pn532_packetbuffer[3] = 0x01; // use IRQ pin!
  
    if (! sendCommandCheckAck(pn532_packetbuffer, 4))
      return false;
  
    // read data packet
    readdata(pn532_packetbuffer, 8);
  
    int offset = _usingSPI ? 5 : 6;
    return  (pn532_packetbuffer[offset] == 0x15);
  }
  
  /**************************************************************************/
  /*!
      Sets the MxRtyPassiveActivation byte of the RFConfiguration register
  
      @param  maxRetries    0xFF to wait forever, 0x00..0xFE to timeout
                            after mxRetries
  
      @returns 1 if everything executed properly, 0 for an error
  */
  /**************************************************************************/
  bool Adafruit_PN532::setPassiveActivationRetries(uint8_t maxRetries) {
    pn532_packetbuffer[0] = PN532_COMMAND_RFCONFIGURATION;
    pn532_packetbuffer[1] = 5;    // Config item 5 (MaxRetries)
    pn532_packetbuffer[2] = 0xFF; // MxRtyATR (default = 0xFF)
    pn532_packetbuffer[3] = 0x01; // MxRtyPSL (default = 0x01)
    pn532_packetbuffer[4] = maxRetries;
  
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.print(F("Setting MxRtyPassiveActivation to ")); PN532DEBUGPRINT.print(maxRetries, DEC); PN532DEBUGPRINT.println(F(" "));
    #endif
  
    if (! sendCommandCheckAck(pn532_packetbuffer, 5))
      return 0x0;  // no ACK
  
    return 1;
  }
  
  /***** ISO14443A Commands ******/
  
  /**************************************************************************/
  /*!
      Waits for an ISO14443A target to enter the field
  
      @param  cardBaudRate  Baud rate of the card
      @param  uid           Pointer to the array that will be populated
                            with the card's UID (up to 7 bytes)
      @param  uidLength     Pointer to the variable that will hold the
                            length of the card's UID.
  
      @returns 1 if everything executed properly, 0 for an error
  */
  /**************************************************************************/
  bool Adafruit_PN532::readPassiveTargetID(uint8_t cardbaudrate, uint8_t * uid, uint8_t * uidLength, uint16_t timeout) {
    pn532_packetbuffer[0] = PN532_COMMAND_INLISTPASSIVETARGET;
    pn532_packetbuffer[1] = 1;  // max 1 cards at once (we can set this to 2 later)
    pn532_packetbuffer[2] = cardbaudrate;
  
    if (!sendCommandCheckAck(pn532_packetbuffer, 3, timeout))
    {
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.println(F("No card(s) read"));
      #endif
      return 0x0;  // no cards read
    }
  
    // wait for a card to enter the field (only possible with I2C)
    if (!_usingSPI) {
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.println(F("Waiting for IRQ (indicates card presence)"));
      #endif
      if (!waitready(timeout)) {
        #ifdef PN532DEBUG
          PN532DEBUGPRINT.println(F("IRQ Timeout"));
        #endif
        return 0x0;
      }
    }
  
    // read data packet
    readdata(pn532_packetbuffer, 20);
    // check some basic stuff
  
    /* ISO14443A card response should be in the following format:
  
      byte            Description
      -------------   ------------------------------------------
      b0..6           Frame header and preamble
      b7              Tags Found
      b8              Tag Number (only one used in this example)
      b9..10          SENS_RES
      b11             SEL_RES
      b12             NFCID Length
      b13..NFCIDLen   NFCID                                      */
  
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.print(F("Found ")); PN532DEBUGPRINT.print(pn532_packetbuffer[7], DEC); PN532DEBUGPRINT.println(F(" tags"));
    #endif
    if (pn532_packetbuffer[7] != 1)
      return 0;
  
    uint16_t sens_res = pn532_packetbuffer[9];
    sens_res <<= 8;
    sens_res |= pn532_packetbuffer[10];
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.print(F("ATQA: 0x"));  PN532DEBUGPRINT.println(sens_res, HEX);
      PN532DEBUGPRINT.print(F("SAK: 0x"));  PN532DEBUGPRINT.println(pn532_packetbuffer[11], HEX);
    #endif
  
    /* Card appears to be Mifare Classic */
    *uidLength = pn532_packetbuffer[12];
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.print(F("UID:"));
    #endif
    for (uint8_t i=0; i < pn532_packetbuffer[12]; i++)
    {
      uid[i] = pn532_packetbuffer[13+i];
      #ifdef MIFAREDEBUG
        PN532DEBUGPRINT.print(F(" 0x"));PN532DEBUGPRINT.print(uid[i], HEX);
      #endif
    }
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.println();
    #endif
  
    return 1;
  }
  
  /**************************************************************************/
  /*!
      @brief  Exchanges an APDU with the currently inlisted peer
  
      @param  send            Pointer to data to send
      @param  sendLength      Length of the data to send
      @param  response        Pointer to response data
      @param  responseLength  Pointer to the response data length
  */
  /**************************************************************************/
  bool Adafruit_PN532::inDataExchange(uint8_t * send, uint8_t sendLength, uint8_t * response, uint8_t * responseLength) {
    if (sendLength > PN532_PACKBUFFSIZ-2) {
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.println(F("APDU length too long for packet buffer"));
      #endif
      return false;
    }
    uint8_t i;
  
    pn532_packetbuffer[0] = 0x40; // PN532_COMMAND_INDATAEXCHANGE;
    pn532_packetbuffer[1] = _inListedTag;
    for (i=0; i<sendLength; ++i) {
      pn532_packetbuffer[i+2] = send[i];
    }
  
    if (!sendCommandCheckAck(pn532_packetbuffer,sendLength+2,1000)) {
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.println(F("Could not send APDU"));
      #endif
      return false;
    }
  
    if (!waitready(1000)) {
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.println(F("Response never received for APDU..."));
      #endif
      return false;
    }
  
    readdata(pn532_packetbuffer,sizeof(pn532_packetbuffer));
  
    if (pn532_packetbuffer[0] == 0 && pn532_packetbuffer[1] == 0 && pn532_packetbuffer[2] == 0xff) {
      uint8_t length = pn532_packetbuffer[3];
      if (pn532_packetbuffer[4]!=(uint8_t)(~length+1)) {
        #ifdef PN532DEBUG
          PN532DEBUGPRINT.println(F("Length check invalid"));
          PN532DEBUGPRINT.println(length,HEX);
          PN532DEBUGPRINT.println((~length)+1,HEX);
        #endif
        return false;
      }
      if (pn532_packetbuffer[5]==PN532_PN532TOHOST && pn532_packetbuffer[6]==PN532_RESPONSE_INDATAEXCHANGE) {
        if ((pn532_packetbuffer[7] & 0x3f)!=0) {
          #ifdef PN532DEBUG
            PN532DEBUGPRINT.println(F("Status code indicates an error"));
          #endif
          return false;
        }
  
        length -= 3;
  
        if (length > *responseLength) {
          length = *responseLength; // silent truncation...
        }
  
        for (i=0; i<length; ++i) {
          response[i] = pn532_packetbuffer[8+i];
        }
        *responseLength = length;
  
        return true;
      }
      else {
        PN532DEBUGPRINT.print(F("Don't know how to handle this command: "));
        PN532DEBUGPRINT.println(pn532_packetbuffer[6],HEX);
        return false;
      }
    }
    else {
      PN532DEBUGPRINT.println(F("Preamble missing"));
      return false;
    }
  }
  
  /**************************************************************************/
  /*!
      @brief  'InLists' a passive target. PN532 acting as reader/initiator,
              peer acting as card/responder.
  */
  /**************************************************************************/
  bool Adafruit_PN532::inListPassiveTarget() {
    pn532_packetbuffer[0] = PN532_COMMAND_INLISTPASSIVETARGET;
    pn532_packetbuffer[1] = 1;
    pn532_packetbuffer[2] = 0;
  
    #ifdef PN532DEBUG
      PN532DEBUGPRINT.print(F("About to inList passive target"));
    #endif
  
    if (!sendCommandCheckAck(pn532_packetbuffer,3,1000)) {
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.println(F("Could not send inlist message"));
      #endif
      return false;
    }
  
    if (!waitready(30000)) {
      return false;
    }
  
    readdata(pn532_packetbuffer,sizeof(pn532_packetbuffer));
  
    if (pn532_packetbuffer[0] == 0 && pn532_packetbuffer[1] == 0 && pn532_packetbuffer[2] == 0xff) {
      uint8_t length = pn532_packetbuffer[3];
      if (pn532_packetbuffer[4]!=(uint8_t)(~length+1)) {
        #ifdef PN532DEBUG
          PN532DEBUGPRINT.println(F("Length check invalid"));
          PN532DEBUGPRINT.println(length,HEX);
          PN532DEBUGPRINT.println((~length)+1,HEX);
        #endif
        return false;
      }
      if (pn532_packetbuffer[5]==PN532_PN532TOHOST && pn532_packetbuffer[6]==PN532_RESPONSE_INLISTPASSIVETARGET) {
        if (pn532_packetbuffer[7] != 1) {
          #ifdef PN532DEBUG
          PN532DEBUGPRINT.println(F("Unhandled number of targets inlisted"));
          #endif
          PN532DEBUGPRINT.println(F("Number of tags inlisted:"));
          PN532DEBUGPRINT.println(pn532_packetbuffer[7]);
          return false;
        }
  
        _inListedTag = pn532_packetbuffer[8];
        PN532DEBUGPRINT.print(F("Tag number: "));
        PN532DEBUGPRINT.println(_inListedTag);
  
        return true;
      } else {
        #ifdef PN532DEBUG
          PN532DEBUGPRINT.print(F("Unexpected response to inlist passive host"));
        #endif
        return false;
      }
    }
    else {
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.println(F("Preamble missing"));
      #endif
      return false;
    }
  
    return true;
  }
  
  
  /***** Mifare Classic Functions ******/
  
  /**************************************************************************/
  /*!
        Indicates whether the specified block number is the first block
        in the sector (block 0 relative to the current sector)
  */
  /**************************************************************************/
  bool Adafruit_PN532::mifareclassic_IsFirstBlock (uint32_t uiBlock)
  {
    // Test if we are in the small or big sectors
    if (uiBlock < 128)
      return ((uiBlock) % 4 == 0);
    else
      return ((uiBlock) % 16 == 0);
  }
  
  /**************************************************************************/
  /*!
        Indicates whether the specified block number is the sector trailer
  */
  /**************************************************************************/
  bool Adafruit_PN532::mifareclassic_IsTrailerBlock (uint32_t uiBlock)
  {
    // Test if we are in the small or big sectors
    if (uiBlock < 128)
      return ((uiBlock + 1) % 4 == 0);
    else
      return ((uiBlock + 1) % 16 == 0);
  }
  
  /**************************************************************************/
  /*!
      Tries to authenticate a block of memory on a MIFARE card using the
      INDATAEXCHANGE command.  See section 7.3.8 of the PN532 User Manual
      for more information on sending MIFARE and other commands.
  
      @param  uid           Pointer to a byte array containing the card UID
      @param  uidLen        The length (in bytes) of the card's UID (Should
                            be 4 for MIFARE Classic)
      @param  blockNumber   The block number to authenticate.  (0..63 for
                            1KB cards, and 0..255 for 4KB cards).
      @param  keyNumber     Which key type to use during authentication
                            (0 = MIFARE_CMD_AUTH_A, 1 = MIFARE_CMD_AUTH_B)
      @param  keyData       Pointer to a byte array containing the 6 byte
                            key value
  
      @returns 1 if everything executed properly, 0 for an error
  */
  /**************************************************************************/
  uint8_t Adafruit_PN532::mifareclassic_AuthenticateBlock (uint8_t * uid, uint8_t uidLen, uint32_t blockNumber, uint8_t keyNumber, uint8_t * keyData)
  {
    uint8_t len;
    uint8_t i;
  
    // Hang on to the key and uid data
    memcpy (_key, keyData, 6);
    memcpy (_uid, uid, uidLen);
    _uidLen = uidLen;
  
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.print(F("Trying to authenticate card "));
      Adafruit_PN532::PrintHex(_uid, _uidLen);
      PN532DEBUGPRINT.print(F("Using authentication KEY "));PN532DEBUGPRINT.print(keyNumber ? 'B' : 'A');PN532DEBUGPRINT.print(F(": "));
      Adafruit_PN532::PrintHex(_key, 6);
    #endif
  
    // Prepare the authentication command //
    pn532_packetbuffer[0] = PN532_COMMAND_INDATAEXCHANGE;   /* Data Exchange Header */
    pn532_packetbuffer[1] = 1;                              /* Max card numbers */
    pn532_packetbuffer[2] = (keyNumber) ? MIFARE_CMD_AUTH_B : MIFARE_CMD_AUTH_A;
    pn532_packetbuffer[3] = blockNumber;                    /* Block Number (1K = 0..63, 4K = 0..255 */
    memcpy (pn532_packetbuffer+4, _key, 6);
    for (i = 0; i < _uidLen; i++)
    {
      pn532_packetbuffer[10+i] = _uid[i];                /* 4 byte card ID */
    }
  
    if (! sendCommandCheckAck(pn532_packetbuffer, 10+_uidLen))
      return 0;
  
    // Read the response packet
    readdata(pn532_packetbuffer, 12);
  
    // check if the response is valid and we are authenticated???
    // for an auth success it should be bytes 5-7: 0xD5 0x41 0x00
    // Mifare auth error is technically byte 7: 0x14 but anything other and 0x00 is not good
    if (pn532_packetbuffer[7] != 0x00)
    {
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.print(F("Authentification failed: "));
        Adafruit_PN532::PrintHexChar(pn532_packetbuffer, 12);
      #endif
      return 0;
    }
  
    return 1;
  }
  
  /**************************************************************************/
  /*!
      Tries to read an entire 16-byte data block at the specified block
      address.
  
      @param  blockNumber   The block number to authenticate.  (0..63 for
                            1KB cards, and 0..255 for 4KB cards).
      @param  data          Pointer to the byte array that will hold the
                            retrieved data (if any)
  
      @returns 1 if everything executed properly, 0 for an error
  */
  /**************************************************************************/
  uint8_t Adafruit_PN532::mifareclassic_ReadDataBlock (uint8_t blockNumber, uint8_t * data)
  {
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.print(F("Trying to read 16 bytes from block "));PN532DEBUGPRINT.println(blockNumber);
    #endif
  
    /* Prepare the command */
    pn532_packetbuffer[0] = PN532_COMMAND_INDATAEXCHANGE;
    pn532_packetbuffer[1] = 1;                      /* Card number */
    pn532_packetbuffer[2] = MIFARE_CMD_READ;        /* Mifare Read command = 0x30 */
    pn532_packetbuffer[3] = blockNumber;            /* Block Number (0..63 for 1K, 0..255 for 4K) */
  
    /* Send the command */
    if (! sendCommandCheckAck(pn532_packetbuffer, 4))
    {
      #ifdef MIFAREDEBUG
        PN532DEBUGPRINT.println(F("Failed to receive ACK for read command"));
      #endif
      return 0;
    }
  
    /* Read the response packet */
    readdata(pn532_packetbuffer, 26);
  
    /* If byte 8 isn't 0x00 we probably have an error */
    if (pn532_packetbuffer[7] != 0x00)
    {
      #ifdef MIFAREDEBUG
        PN532DEBUGPRINT.println(F("Unexpected response"));
        Adafruit_PN532::PrintHexChar(pn532_packetbuffer, 26);
      #endif
      return 0;
    }
  
    /* Copy the 16 data bytes to the output buffer        */
    /* Block content starts at byte 9 of a valid response */
    memcpy (data, pn532_packetbuffer+8, 16);
  
    /* Display data for debug if requested */
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.print(F("Block "));
      PN532DEBUGPRINT.println(blockNumber);
      Adafruit_PN532::PrintHexChar(data, 16);
    #endif
  
    return 1;
  }
  
  /**************************************************************************/
  /*!
      Tries to write an entire 16-byte data block at the specified block
      address.
  
      @param  blockNumber   The block number to authenticate.  (0..63 for
                            1KB cards, and 0..255 for 4KB cards).
      @param  data          The byte array that contains the data to write.
  
      @returns 1 if everything executed properly, 0 for an error
  */
  /**************************************************************************/
  uint8_t Adafruit_PN532::mifareclassic_WriteDataBlock (uint8_t blockNumber, uint8_t * data)
  {
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.print(F("Trying to write 16 bytes to block "));PN532DEBUGPRINT.println(blockNumber);
    #endif
  
    /* Prepare the first command */
    pn532_packetbuffer[0] = PN532_COMMAND_INDATAEXCHANGE;
    pn532_packetbuffer[1] = 1;                      /* Card number */
    pn532_packetbuffer[2] = MIFARE_CMD_WRITE;       /* Mifare Write command = 0xA0 */
    pn532_packetbuffer[3] = blockNumber;            /* Block Number (0..63 for 1K, 0..255 for 4K) */
    memcpy (pn532_packetbuffer+4, data, 16);          /* Data Payload */
  
    /* Send the command */
    if (! sendCommandCheckAck(pn532_packetbuffer, 20))
    {
      #ifdef MIFAREDEBUG
        PN532DEBUGPRINT.println(F("Failed to receive ACK for write command"));
      #endif
      return 0;
    }
    delay(10);
  
    /* Read the response packet */
    readdata(pn532_packetbuffer, 26);
  
    return 1;
  }
  
  /**************************************************************************/
  /*!
      Formats a Mifare Classic card to store NDEF Records
  
      @returns 1 if everything executed properly, 0 for an error
  */
  /**************************************************************************/
  uint8_t Adafruit_PN532::mifareclassic_FormatNDEF (void)
  {
    uint8_t sectorbuffer1[16] = {0x14, 0x01, 0x03, 0xE1, 0x03, 0xE1, 0x03, 0xE1, 0x03, 0xE1, 0x03, 0xE1, 0x03, 0xE1, 0x03, 0xE1};
    uint8_t sectorbuffer2[16] = {0x03, 0xE1, 0x03, 0xE1, 0x03, 0xE1, 0x03, 0xE1, 0x03, 0xE1, 0x03, 0xE1, 0x03, 0xE1, 0x03, 0xE1};
    uint8_t sectorbuffer3[16] = {0xA0, 0xA1, 0xA2, 0xA3, 0xA4, 0xA5, 0x78, 0x77, 0x88, 0xC1, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};
  
    // Note 0xA0 0xA1 0xA2 0xA3 0xA4 0xA5 must be used for key A
    // for the MAD sector in NDEF records (sector 0)
  
    // Write block 1 and 2 to the card
    if (!(mifareclassic_WriteDataBlock (1, sectorbuffer1)))
      return 0;
    if (!(mifareclassic_WriteDataBlock (2, sectorbuffer2)))
      return 0;
    // Write key A and access rights card
    if (!(mifareclassic_WriteDataBlock (3, sectorbuffer3)))
      return 0;
  
    // Seems that everything was OK (?!)
    return 1;
  }
  
  /**************************************************************************/
  /*!
      Writes an NDEF URI Record to the specified sector (1..15)
  
      Note that this function assumes that the Mifare Classic card is
      already formatted to work as an "NFC Forum Tag" and uses a MAD1
      file system.  You can use the NXP TagWriter app on Android to
      properly format cards for this.
  
      @param  sectorNumber  The sector that the URI record should be written
                            to (can be 1..15 for a 1K card)
      @param  uriIdentifier The uri identifier code (0 = none, 0x01 =
                            "http://www.", etc.)
      @param  url           The uri text to write (max 38 characters).
  
      @returns 1 if everything executed properly, 0 for an error
  */
  /**************************************************************************/
  uint8_t Adafruit_PN532::mifareclassic_WriteNDEFURI (uint8_t sectorNumber, uint8_t uriIdentifier, const char * url)
  {
    // Figure out how long the string is
    uint8_t len = strlen(url);
  
    // Make sure we're within a 1K limit for the sector number
    if ((sectorNumber < 1) || (sectorNumber > 15))
      return 0;
  
    // Make sure the URI payload is between 1 and 38 chars
    if ((len < 1) || (len > 38))
      return 0;
  
    // Note 0xD3 0xF7 0xD3 0xF7 0xD3 0xF7 must be used for key A
    // in NDEF records
  
    // Setup the sector buffer (w/pre-formatted TLV wrapper and NDEF message)
    uint8_t sectorbuffer1[16] = {0x00, 0x00, 0x03, len+5, 0xD1, 0x01, len+1, 0x55, uriIdentifier, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
    uint8_t sectorbuffer2[16] = {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
    uint8_t sectorbuffer3[16] = {0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
    uint8_t sectorbuffer4[16] = {0xD3, 0xF7, 0xD3, 0xF7, 0xD3, 0xF7, 0x7F, 0x07, 0x88, 0x40, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};
    if (len <= 6)
    {
      // Unlikely we'll get a url this short, but why not ...
      memcpy (sectorbuffer1+9, url, len);
      sectorbuffer1[len+9] = 0xFE;
    }
    else if (len == 7)
    {
      // 0xFE needs to be wrapped around to next block
      memcpy (sectorbuffer1+9, url, len);
      sectorbuffer2[0] = 0xFE;
    }
    else if ((len > 7) && (len <= 22))
    {
      // Url fits in two blocks
      memcpy (sectorbuffer1+9, url, 7);
      memcpy (sectorbuffer2, url+7, len-7);
      sectorbuffer2[len-7] = 0xFE;
    }
    else if (len == 23)
    {
      // 0xFE needs to be wrapped around to final block
      memcpy (sectorbuffer1+9, url, 7);
      memcpy (sectorbuffer2, url+7, len-7);
      sectorbuffer3[0] = 0xFE;
    }
    else
    {
      // Url fits in three blocks
      memcpy (sectorbuffer1+9, url, 7);
      memcpy (sectorbuffer2, url+7, 16);
      memcpy (sectorbuffer3, url+23, len-24);
      sectorbuffer3[len-22] = 0xFE;
    }
  
    // Now write all three blocks back to the card
    if (!(mifareclassic_WriteDataBlock (sectorNumber*4, sectorbuffer1)))
      return 0;
    if (!(mifareclassic_WriteDataBlock ((sectorNumber*4)+1, sectorbuffer2)))
      return 0;
    if (!(mifareclassic_WriteDataBlock ((sectorNumber*4)+2, sectorbuffer3)))
      return 0;
    if (!(mifareclassic_WriteDataBlock ((sectorNumber*4)+3, sectorbuffer4)))
      return 0;
  
    // Seems that everything was OK (?!)
    return 1;
  }
  
  /***** Mifare Ultralight Functions ******/
  
  /**************************************************************************/
  /*!
      Tries to read an entire 4-byte page at the specified address.
  
      @param  page        The page number (0..63 in most cases)
      @param  buffer      Pointer to the byte array that will hold the
                          retrieved data (if any)
  */
  /**************************************************************************/
  uint8_t Adafruit_PN532::mifareultralight_ReadPage (uint8_t page, uint8_t * buffer)
  {
    if (page >= 64)
    {
      #ifdef MIFAREDEBUG
        PN532DEBUGPRINT.println(F("Page value out of range"));
      #endif
      return 0;
    }
  
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.print(F("Reading page "));PN532DEBUGPRINT.println(page);
    #endif
  
    /* Prepare the command */
    pn532_packetbuffer[0] = PN532_COMMAND_INDATAEXCHANGE;
    pn532_packetbuffer[1] = 1;                   /* Card number */
    pn532_packetbuffer[2] = MIFARE_CMD_READ;     /* Mifare Read command = 0x30 */
    pn532_packetbuffer[3] = page;                /* Page Number (0..63 in most cases) */
  
    /* Send the command */
    if (! sendCommandCheckAck(pn532_packetbuffer, 4))
    {
      #ifdef MIFAREDEBUG
        PN532DEBUGPRINT.println(F("Failed to receive ACK for write command"));
      #endif
      return 0;
    }
  
    /* Read the response packet */
    readdata(pn532_packetbuffer, 26);
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.println(F("Received: "));
      Adafruit_PN532::PrintHexChar(pn532_packetbuffer, 26);
    #endif
  
    /* If byte 8 isn't 0x00 we probably have an error */
    if (pn532_packetbuffer[7] == 0x00)
    {
      /* Copy the 4 data bytes to the output buffer         */
      /* Block content starts at byte 9 of a valid response */
      /* Note that the command actually reads 16 byte or 4  */
      /* pages at a time ... we simply discard the last 12  */
      /* bytes                                              */
      memcpy (buffer, pn532_packetbuffer+8, 4);
    }
    else
    {
      #ifdef MIFAREDEBUG
        PN532DEBUGPRINT.println(F("Unexpected response reading block: "));
        Adafruit_PN532::PrintHexChar(pn532_packetbuffer, 26);
      #endif
      return 0;
    }
  
    /* Display data for debug if requested */
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.print(F("Page "));PN532DEBUGPRINT.print(page);PN532DEBUGPRINT.println(F(":"));
      Adafruit_PN532::PrintHexChar(buffer, 4);
    #endif
  
    // Return OK signal
    return 1;
  }
  
  /**************************************************************************/
  /*!
      Tries to write an entire 4-byte page at the specified block
      address.
  
      @param  page          The page number to write.  (0..63 for most cases)
      @param  data          The byte array that contains the data to write.
                            Should be exactly 4 bytes long.
  
      @returns 1 if everything executed properly, 0 for an error
  */
  /**************************************************************************/
  uint8_t Adafruit_PN532::mifareultralight_WritePage (uint8_t page, uint8_t * data)
  {
  
    if (page >= 64)
    {
      #ifdef MIFAREDEBUG
        PN532DEBUGPRINT.println(F("Page value out of range"));
      #endif
      // Return Failed Signal
      return 0;
    }
  
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.print(F("Trying to write 4 byte page"));PN532DEBUGPRINT.println(page);
    #endif
  
    /* Prepare the first command */
    pn532_packetbuffer[0] = PN532_COMMAND_INDATAEXCHANGE;
    pn532_packetbuffer[1] = 1;                      /* Card number */
    pn532_packetbuffer[2] = MIFARE_ULTRALIGHT_CMD_WRITE;       /* Mifare Ultralight Write command = 0xA2 */
    pn532_packetbuffer[3] = page;            /* Page Number (0..63 for most cases) */
    memcpy (pn532_packetbuffer+4, data, 4);          /* Data Payload */
  
    /* Send the command */
    if (! sendCommandCheckAck(pn532_packetbuffer, 8))
    {
      #ifdef MIFAREDEBUG
        PN532DEBUGPRINT.println(F("Failed to receive ACK for write command"));
      #endif
  
      // Return Failed Signal
      return 0;
    }
    delay(10);
  
    /* Read the response packet */
    readdata(pn532_packetbuffer, 26);
  
    // Return OK Signal
    return 1;
  }
  
  
  /***** NTAG2xx Functions ******/
  
  /**************************************************************************/
  /*!
      Tries to read an entire 4-byte page at the specified address.
  
      @param  page        The page number (0..63 in most cases)
      @param  buffer      Pointer to the byte array that will hold the
                          retrieved data (if any)
  */
  /**************************************************************************/
  uint8_t Adafruit_PN532::ntag2xx_ReadPage (uint8_t page, uint8_t * buffer)
  {
    // TAG Type       PAGES   USER START    USER STOP
    // --------       -----   ----------    ---------
    // NTAG 203       42      4             39
    // NTAG 213       45      4             39
    // NTAG 215       135     4             129
    // NTAG 216       231     4             225
  
    if (page >= 231)
    {
      #ifdef MIFAREDEBUG
        PN532DEBUGPRINT.println(F("Page value out of range"));
      #endif
      return 0;
    }
  
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.print(F("Reading page "));PN532DEBUGPRINT.println(page);
    #endif
  
    /* Prepare the command */
    pn532_packetbuffer[0] = PN532_COMMAND_INDATAEXCHANGE;
    pn532_packetbuffer[1] = 1;                   /* Card number */
    pn532_packetbuffer[2] = MIFARE_CMD_READ;     /* Mifare Read command = 0x30 */
    pn532_packetbuffer[3] = page;                /* Page Number (0..63 in most cases) */
  
    /* Send the command */
    if (! sendCommandCheckAck(pn532_packetbuffer, 4))
    {
      #ifdef MIFAREDEBUG
        PN532DEBUGPRINT.println(F("Failed to receive ACK for write command"));
      #endif
      return 0;
    }
  
    /* Read the response packet */
    readdata(pn532_packetbuffer, 26);
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.println(F("Received: "));
      Adafruit_PN532::PrintHexChar(pn532_packetbuffer, 26);
    #endif
  
    /* If byte 8 isn't 0x00 we probably have an error */
    if (pn532_packetbuffer[7] == 0x00)
    {
      /* Copy the 4 data bytes to the output buffer         */
      /* Block content starts at byte 9 of a valid response */
      /* Note that the command actually reads 16 byte or 4  */
      /* pages at a time ... we simply discard the last 12  */
      /* bytes                                              */
      memcpy (buffer, pn532_packetbuffer+8, 4);
    }
    else
    {
      #ifdef MIFAREDEBUG
        PN532DEBUGPRINT.println(F("Unexpected response reading block: "));
        Adafruit_PN532::PrintHexChar(pn532_packetbuffer, 26);
      #endif
      return 0;
    }
  
    /* Display data for debug if requested */
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.print(F("Page "));PN532DEBUGPRINT.print(page);PN532DEBUGPRINT.println(F(":"));
      Adafruit_PN532::PrintHexChar(buffer, 4);
    #endif
  
    // Return OK signal
    return 1;
  }
  
  /**************************************************************************/
  /*!
      Tries to write an entire 4-byte page at the specified block
      address.
  
      @param  page          The page number to write.  (0..63 for most cases)
      @param  data          The byte array that contains the data to write.
                            Should be exactly 4 bytes long.
  
      @returns 1 if everything executed properly, 0 for an error
  */
  /**************************************************************************/
  uint8_t Adafruit_PN532::ntag2xx_WritePage (uint8_t page, uint8_t * data)
  {
    // TAG Type       PAGES   USER START    USER STOP
    // --------       -----   ----------    ---------
    // NTAG 203       42      4             39
    // NTAG 213       45      4             39
    // NTAG 215       135     4             129
    // NTAG 216       231     4             225
  
    if ((page < 4) || (page > 225))
    {
      #ifdef MIFAREDEBUG
        PN532DEBUGPRINT.println(F("Page value out of range"));
      #endif
      // Return Failed Signal
      return 0;
    }
  
    #ifdef MIFAREDEBUG
      PN532DEBUGPRINT.print(F("Trying to write 4 byte page"));PN532DEBUGPRINT.println(page);
    #endif
  
    /* Prepare the first command */
    pn532_packetbuffer[0] = PN532_COMMAND_INDATAEXCHANGE;
    pn532_packetbuffer[1] = 1;                              /* Card number */
    pn532_packetbuffer[2] = MIFARE_ULTRALIGHT_CMD_WRITE;    /* Mifare Ultralight Write command = 0xA2 */
    pn532_packetbuffer[3] = page;                           /* Page Number (0..63 for most cases) */
    memcpy (pn532_packetbuffer+4, data, 4);                 /* Data Payload */
  
    /* Send the command */
    if (! sendCommandCheckAck(pn532_packetbuffer, 8))
    {
      #ifdef MIFAREDEBUG
        PN532DEBUGPRINT.println(F("Failed to receive ACK for write command"));
      #endif
  
      // Return Failed Signal
      return 0;
    }
    delay(10);
  
    /* Read the response packet */
    readdata(pn532_packetbuffer, 26);
  
    // Return OK Signal
    return 1;
  }
  
  /**************************************************************************/
  /*!
      Writes an NDEF URI Record starting at the specified page (4..nn)
  
      Note that this function assumes that the NTAG2xx card is
      already formatted to work as an "NFC Forum Tag".
  
      @param  uriIdentifier The uri identifier code (0 = none, 0x01 =
                            "http://www.", etc.)
      @param  url           The uri text to write (null-terminated string).
      @param  dataLen       The size of the data area for overflow checks.
  
      @returns 1 if everything executed properly, 0 for an error
  */
  /**************************************************************************/
  uint8_t Adafruit_PN532::ntag2xx_WriteNDEFURI (uint8_t uriIdentifier, char * url, uint8_t dataLen)
  {
    uint8_t pageBuffer[4] = { 0, 0, 0, 0 };
  
    // Remove NDEF record overhead from the URI data (pageHeader below)
    uint8_t wrapperSize = 12;
  
    // Figure out how long the string is
    uint8_t len = strlen(url);
  
    // Make sure the URI payload will fit in dataLen (include 0xFE trailer)
    if ((len < 1) || (len+1 > (dataLen-wrapperSize)))
      return 0;
  
    // Setup the record header
    // See NFCForum-TS-Type-2-Tag_1.1.pdf for details
    uint8_t pageHeader[12] =
    {
      /* NDEF Lock Control TLV (must be first and always present) */
      0x01,         /* Tag Field (0x01 = Lock Control TLV) */
      0x03,         /* Payload Length (always 3) */
      0xA0,         /* The position inside the tag of the lock bytes (upper 4 = page address, lower 4 = byte offset) */
      0x10,         /* Size in bits of the lock area */
      0x44,         /* Size in bytes of a page and the number of bytes each lock bit can lock (4 bit + 4 bits) */
      /* NDEF Message TLV - URI Record */
      0x03,         /* Tag Field (0x03 = NDEF Message) */
      len+5,        /* Payload Length (not including 0xFE trailer) */
      0xD1,         /* NDEF Record Header (TNF=0x1:Well known record + SR + ME + MB) */
      0x01,         /* Type Length for the record type indicator */
      len+1,        /* Payload len */
      0x55,         /* Record Type Indicator (0x55 or 'U' = URI Record) */
      uriIdentifier /* URI Prefix (ex. 0x01 = "http://www.") */
    };
  
    // Write 12 byte header (three pages of data starting at page 4)
    memcpy (pageBuffer, pageHeader, 4);
    if (!(ntag2xx_WritePage (4, pageBuffer)))
      return 0;
    memcpy (pageBuffer, pageHeader+4, 4);
    if (!(ntag2xx_WritePage (5, pageBuffer)))
      return 0;
    memcpy (pageBuffer, pageHeader+8, 4);
    if (!(ntag2xx_WritePage (6, pageBuffer)))
      return 0;
  
    // Write URI (starting at page 7)
    uint8_t currentPage = 7;
    char * urlcopy = url;
    while(len)
    {
      if (len < 4)
      {
        memset(pageBuffer, 0, 4);
        memcpy(pageBuffer, urlcopy, len);
        pageBuffer[len] = 0xFE; // NDEF record footer
        if (!(ntag2xx_WritePage (currentPage, pageBuffer)))
          return 0;
        // DONE!
        return 1;
      }
      else if (len == 4)
      {
        memcpy(pageBuffer, urlcopy, len);
        if (!(ntag2xx_WritePage (currentPage, pageBuffer)))
          return 0;
        memset(pageBuffer, 0, 4);
        pageBuffer[0] = 0xFE; // NDEF record footer
        currentPage++;
        if (!(ntag2xx_WritePage (currentPage, pageBuffer)))
          return 0;
        // DONE!
        return 1;
      }
      else
      {
        // More than one page of data left
        memcpy(pageBuffer, urlcopy, 4);
        if (!(ntag2xx_WritePage (currentPage, pageBuffer)))
          return 0;
        currentPage++;
        urlcopy+=4;
        len-=4;
      }
    }
  
    // Seems that everything was OK (?!)
    return 1;
  }
  
  
  /************** high level communication functions (handles both I2C and SPI) */
  
  
  /**************************************************************************/
  /*!
      @brief  Tries to read the SPI or I2C ACK signal
  */
  /**************************************************************************/
  bool Adafruit_PN532::readack() {
    uint8_t ackbuff[6];
  
    readdata(ackbuff, 6);
  
    return (0 == strncmp((char *)ackbuff, (char *)pn532ack, 6));
  }
  
  
  /**************************************************************************/
  /*!
      @brief  Return true if the PN532 is ready with a response.
  */
  /**************************************************************************/
  bool Adafruit_PN532::isready() {
    if (_usingSPI) {
      // SPI read status and check if ready.
      #ifdef SPI_HAS_TRANSACTION
        if (_hardwareSPI) SPI.beginTransaction(PN532_SPI_SETTING);
      #endif
      digitalWrite(_ss, LOW);
      delay(2);
      spi_write(PN532_SPI_STATREAD);
      // read byte
      uint8_t x = spi_read();
  
      digitalWrite(_ss, HIGH);
      #ifdef SPI_HAS_TRANSACTION
        if (_hardwareSPI) SPI.endTransaction();
      #endif
  
      // Check if status is ready.
      return x == PN532_SPI_READY;
    }
    else {
      // I2C check if status is ready by IRQ line being pulled low.
      uint8_t x = digitalRead(_irq);
      return x == 0;
    }
  }
  
  /**************************************************************************/
  /*!
      @brief  Waits until the PN532 is ready.
  
      @param  timeout   Timeout before giving up
  */
  /**************************************************************************/
  bool Adafruit_PN532::waitready(uint16_t timeout) {
    uint16_t timer = 0;
    while(!isready()) {
      if (timeout != 0) {
        timer += 10;
        if (timer > timeout) {
          PN532DEBUGPRINT.println("TIMEOUT!");
          return false;
        }
      }
      delay(10);
    }
    return true;
  }
  
  /**************************************************************************/
  /*!
      @brief  Reads n bytes of data from the PN532 via SPI or I2C.
  
      @param  buff      Pointer to the buffer where data will be written
      @param  n         Number of bytes to be read
  */
  /**************************************************************************/
  void Adafruit_PN532::readdata(uint8_t* buff, uint8_t n) {
    if (_usingSPI) {
      // SPI write.
      #ifdef SPI_HAS_TRANSACTION
        if (_hardwareSPI) SPI.beginTransaction(PN532_SPI_SETTING);
      #endif
      digitalWrite(_ss, LOW);
      delay(2);
      spi_write(PN532_SPI_DATAREAD);
  
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.print(F("Reading: "));
      #endif
      for (uint8_t i=0; i<n; i++) {
        delay(1);
        buff[i] = spi_read();
        #ifdef PN532DEBUG
          PN532DEBUGPRINT.print(F(" 0x"));
          PN532DEBUGPRINT.print(buff[i], HEX);
        #endif
      }
  
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.println();
      #endif
  
      digitalWrite(_ss, HIGH);
      #ifdef SPI_HAS_TRANSACTION
        if (_hardwareSPI) SPI.endTransaction();
      #endif
    }
    else {
      // I2C write.
      uint16_t timer = 0;
  
      delay(2);
  
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.print(F("Reading: "));
      #endif
      // Start read (n+1 to take into account leading 0x01 with I2C)
      WIRE.requestFrom((uint8_t)PN532_I2C_ADDRESS, (uint8_t)(n+2));
      // Discard the leading 0x01
      i2c_recv();
      for (uint8_t i=0; i<n; i++) {
        delay(1);
        buff[i] = i2c_recv();
        #ifdef PN532DEBUG
          PN532DEBUGPRINT.print(F(" 0x"));
          PN532DEBUGPRINT.print(buff[i], HEX);
        #endif
      }
      // Discard trailing 0x00 0x00
      // i2c_recv();
  
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.println();
      #endif
    }
  }
  
  /**************************************************************************/
  /*!
      @brief  Writes a command to the PN532, automatically inserting the
              preamble and required frame details (checksum, len, etc.)
  
      @param  cmd       Pointer to the command buffer
      @param  cmdlen    Command length in bytes
  */
  /**************************************************************************/
  void Adafruit_PN532::writecommand(uint8_t* cmd, uint8_t cmdlen) {
    if (_usingSPI) {
      // SPI command write.
      uint8_t checksum;
  
      cmdlen++;
  
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.print(F("\nSending: "));
      #endif
  
      #ifdef SPI_HAS_TRANSACTION
        if (_hardwareSPI) SPI.beginTransaction(PN532_SPI_SETTING);
      #endif
      digitalWrite(_ss, LOW);
      delay(2);     // or whatever the delay is for waking up the board
      spi_write(PN532_SPI_DATAWRITE);
  
      checksum = PN532_PREAMBLE + PN532_PREAMBLE + PN532_STARTCODE2;
      spi_write(PN532_PREAMBLE);
      spi_write(PN532_PREAMBLE);
      spi_write(PN532_STARTCODE2);
  
      spi_write(cmdlen);
      spi_write(~cmdlen + 1);
  
      spi_write(PN532_HOSTTOPN532);
      checksum += PN532_HOSTTOPN532;
  
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(PN532_PREAMBLE, HEX);
        PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(PN532_PREAMBLE, HEX);
        PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(PN532_STARTCODE2, HEX);
        PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(cmdlen, HEX);
        PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(~cmdlen + 1, HEX);
        PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(PN532_HOSTTOPN532, HEX);
      #endif
  
      for (uint8_t i=0; i<cmdlen-1; i++) {
        spi_write(cmd[i]);
        checksum += cmd[i];
        #ifdef PN532DEBUG
          PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(cmd[i], HEX);
        #endif
      }
  
      spi_write(~checksum);
      spi_write(PN532_POSTAMBLE);
      digitalWrite(_ss, HIGH);
      #ifdef SPI_HAS_TRANSACTION
        if (_hardwareSPI) SPI.endTransaction();
      #endif
  
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(~checksum, HEX);
        PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(PN532_POSTAMBLE, HEX);
        PN532DEBUGPRINT.println();
      #endif
    }
    else {
      // I2C command write.
      uint8_t checksum;
  
      cmdlen++;
  
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.print(F("\nSending: "));
      #endif
  
      delay(2);     // or whatever the delay is for waking up the board
  
      // I2C START
      WIRE.beginTransmission(PN532_I2C_ADDRESS);
      checksum = PN532_PREAMBLE + PN532_PREAMBLE + PN532_STARTCODE2;
      i2c_send(PN532_PREAMBLE);
      i2c_send(PN532_PREAMBLE);
      i2c_send(PN532_STARTCODE2);
  
      i2c_send(cmdlen);
      i2c_send(~cmdlen + 1);
  
      i2c_send(PN532_HOSTTOPN532);
      checksum += PN532_HOSTTOPN532;
  
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(PN532_PREAMBLE, HEX);
        PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(PN532_PREAMBLE, HEX);
        PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(PN532_STARTCODE2, HEX);
        PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(cmdlen, HEX);
        PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(~cmdlen + 1, HEX);
        PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(PN532_HOSTTOPN532, HEX);
      #endif
  
      for (uint8_t i=0; i<cmdlen-1; i++) {
        i2c_send(cmd[i]);
        checksum += cmd[i];
        #ifdef PN532DEBUG
          PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(cmd[i], HEX);
        #endif
      }
  
      i2c_send(~checksum);
      i2c_send(PN532_POSTAMBLE);
  
      // I2C STOP
      WIRE.endTransmission();
  
      #ifdef PN532DEBUG
        PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(~checksum, HEX);
        PN532DEBUGPRINT.print(F(" 0x")); PN532DEBUGPRINT.print(PN532_POSTAMBLE, HEX);
        PN532DEBUGPRINT.println();
      #endif
  
    }
  }
  /************** low level SPI */
  
  /**************************************************************************/
  /*!
      @brief  Low-level SPI write wrapper
  
      @param  c       8-bit command to write to the SPI bus
  */
  /**************************************************************************/
  void Adafruit_PN532::spi_write(uint8_t c) {
    if (_hardwareSPI) {
      // Hardware SPI write.
      SPI.transfer(c);
    }
    else {
      // Software SPI write.
      int8_t i;
      digitalWrite(_clk, HIGH);
  
      for (i=0; i<8; i++) {
        digitalWrite(_clk, LOW);
        if (c & _BV(i)) {
          digitalWrite(_mosi, HIGH);
        } else {
          digitalWrite(_mosi, LOW);
        }
        digitalWrite(_clk, HIGH);
      }
    }
  }
  
  /**************************************************************************/
  /*!
      @brief  Low-level SPI read wrapper
  
      @returns The 8-bit value that was read from the SPI bus
  */
  /**************************************************************************/
  uint8_t Adafruit_PN532::spi_read(void) {
    int8_t i, x;
    x = 0;
  
    if (_hardwareSPI) {
      // Hardware SPI read.
      x = SPI.transfer(0x00);
    }
    else {
      // Software SPI read.
      digitalWrite(_clk, HIGH);
  
      for (i=0; i<8; i++) {
        if (digitalRead(_miso)) {
          x |= _BV(i);
        }
        digitalWrite(_clk, LOW);
        digitalWrite(_clk, HIGH);
      }
    }
  
    return x;
  }
  