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2.2.7 MFRC522 RFID Module
==========================

Introduction
---------------

Radio Frequency Identification (RFID) refers to technologies that use
wireless communication between an object (or tag) and interrogating
device (or reader) to automatically track and identify such objects.

Some of the most common applications for this technology include retail
supply chains, military supply chains, automated payment methods,
baggage tracking and management, document tracking and pharmaceutical
management, to name a few.

In this project, we will use RFID for reading and writing.

Components
----------

.. image:: img/list_2.2.7.png


Principle
---------

**RFID**

Radio Frequency Identification (RFID) refers to technologies that
involve using wireless communication between an object (or tag) and an
interrogating device (or reader) to automatically track and identify
such objects. The tag transmission range is limited to several meters
from the reader. A clear line of sight between the reader and tag is not
necessarily required.

Most tags contain at least one integrated circuit (IC) and an antenna.
The microchip stores information and is responsible for managing the
radio frequency (RF) communication with the reader. Passive tags do not
have an independent energy source and depend on an external
electromagnetic signal, provided by the reader, to power their
operations. Active tags contain an independent energy source, such as a
battery. Thus, they may have increased processing, transmission
capabilities and range.

.. image:: img/image230.png


**MFRC522**

MFRC522 is a kind of integrated read and write card chip. It is commonly
used in the radio at 13.56MHz. Launched by the NXP Company, it is a
low-voltage, low-cost, and small-sized non-contact card chip, a best
choice of intelligent instrument and portable handheld device.

The MF RC522 uses advanced modulation and demodulation concept which
fully presented in all types of 13.56MHz passive contactless
communication methods and protocols. In addition, it supports rapid
CRYPTO1 encryption algorithm to verify MIFARE products. MFRC522 also
supports MIFARE series of high-speed non-contact communication, with a
two-way data transmission rate up to 424kbit/s. As a new member of the
13.56MHz highly integrated reader card series, MF RC522 is much similar
to the existing MF RC500 and MF RC530 but there also exists great
differences. It communicates with the host machine via the serial manner
which needs less wiring. You can choose between SPI, I2C and serial UART
mode (similar to RS232), which helps reduce the connection, save PCB
board space (smaller size), and reduce cost.

Schematic Diagram
-----------------

.. image:: img/image331.png


Experimental Procedures
-----------------------

**Step 1:** Build the circuit.

.. image:: img/image232.png
    :width: 800


**Step 2**: Set up SPI (refer to :ref:`spi_configuration` for more details. If you have set SPI, skip this step.)

**Step 3:** Go to the folder of the code.

.. raw:: html

   <run></run>

.. code-block:: 

    cd ~/davinci-kit-for-raspberry-pi/c/2.2.7/

**Step 4:** Compile the code.

.. raw:: html

   <run></run>

.. code-block:: 

    make read
    make write

.. note::
    There are two examples for you to read or write the card ID,
    and you can choose one of them according to your need.

**Step 5:** After running ``./write``, enter the information, such as the name of the person, and then put the tag or card on the MRC522 module and wait for the writing to be completed.

.. raw:: html

   <run></run>

.. code-block::

    sudo ./write

**Step 6:** Now run ``./read`` to read the information of the tag or card you have written.

.. raw:: html

   <run></run>

.. code-block::

    sudo ./read


.. note::

    If it does not work after running, or there is an error prompt: \"wiringPi.h: No such file or directory\", please refer to :ref:`install_wiringpi_pi5`. 

**Code Explanation**

.. code-block:: c

    InitRc522();

This function is used to initialize the RFID RC522 module.

.. code-block:: c

    uint8_t read_card_data();

This function is used to read the data of the card, and if 
the read is successful, it will return "1".

.. code-block:: c

    uint8_t write_card_data(uint8_t *data);

This function is used to write the data of card and returns "1" if 
the write is successful. \*data is the information that will be written 
to the card.