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NFC/RFID Sensors and Modules

RFID reader module: MFRC522

So, hello to all viewers and welcome back to Gettobyte Platform. In This blog you are going to know about RFID Reader MFRC522, which is designed by NXP Semiconductors. Objective would be to interface this module with Host MCU’s like of NXP Semiconductors, STMicroelectronics or other vendors MCU’s. Will make the driver to interface the RFID Reader with any MCU, not unlike just with Arduino and Arduino IDE environment. To make the driver of RFID reader at first, we need to dig into its datasheet, to understand its various sub parts. And that’s all about this blog is gotten going to be, to make the datasheet understand in easy way-out.

MFRC522 Datasheet Explanation

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RFID Technology

RFID modules is a wireless sensing technology which is used to track/identify/monitor the objects.

 Viewers can refer to this blog to know about RFID technology in detail.

or can watch this video which is in animated format to know about RFID technology.


MFRC522 is a highly integrated reader/writer IC for contactless communication at 13.56 MHz. These reader supports the ISO 14443 A protocol for communicating with RFID Tags. They are used to detect the MIFRAME RFID tags.


MFRC522 has internal RF transceiver, which provides a robust and efficient implementation for demodulating and decoding signals from MIFRAME compatible cards using ISO 14443 A protocol. The digital module of MFRC522 manages the complete ISO/IEC 14443 A framing and error detection (parity and CRC) functionality.

MFRC522 supports 3 tags of MIFRAME family, that are MF1xxS20, MF1xxS70 and MF1S50 products.

MFRC522 features

MFRC522 Features

MFRC522 though quite old RFID reader and in today’s time many new advance RFID readers have come up. But so as to get started with this technology as a hobbyist/student/DIY project, it is perfect module to lay your hands on this Technology.

  • MFRC522 has highly integrated analog circuitry to demodulate and decode responses when RFID tags are brought in close proximity of these devices.
  • RFID readers are connected with some host MCU, where the processing of data which is received via RFID tags happens according to the application. MFRC522 can connect with host MCU, using SPI, Serial UART and I2C -bus interface.
  • It supports ISO 14443 A protocol and can be used with MIFRAME family of RFID tags. And in MIFRAME family it supports only MF1xxS20, MF1xxS70 and MF1xxS50 products.
  • It has internal CRC-coprocessor.
  • Internal FIFO buffer which can handle 64 bytes of sending and receiving.
  • It uses the Crypto-1 cipher for authenticating.
  • It supports Internal oscillator for connection to 27.12 MHz quartz crytsal.
  • It is low power device, need 2.5 V to 3.3 V power supply.
  • It also has flexible interrupt modes when some RFID tags are detected and trigering events too. In addition to flexible interrupt, it has programmabe I/O pins and timer.
  • It can perform Internal self-test too.

MFRC522 Functional description

MFRC522 Functional Descriptions

MFRC522 Block Diagram

MFRC522 Block Diagram

Above is the simplified block diagram of MFRC522 module. MFRC522 has an internal memory, power supply, interrupt pins, FIFO buffer, Antenna and analog interface, digital module for communicating with Host MCU. 

Analog Interface handles the modulation and demodulation of the analog signals. FIFO Buffer ensures fast and convenient data transfer.

Register bank are the set of registers through which MFRC522 would be configured and initialized to use. Parameters like Clock, Interrupts, status of errors while communicating with RFID readers, CRC calculation, FIFO configuration and etc need to be configured before using the MFRC522.

How the MFRC522 Internal system works?

Host MCU will send PCD Commands to MFRC522, according to which it will perform some operations. MCU will send these commands by writing into one of the registers of PCD.( For MFRC522 CommandReg is register)

Operations like: 

  • Activation of CRC Coprocessor
  • Transmission of data from FIFO buffer of MFRC522 and activation of receiver circuits to get the response from PICC
  • transfer of data from FIFO to an internal buffer 
  • soft reset and authentication-based operations

Further MFRC522 will emit the commands for communicating with PICC, here referred to as PICC Commands, according to which operation with PICC takes place, like scanning of PICC, selecting the PICC, reading and writing the data on PICC. MFRC522 emits these commands via electromagnetic induction and electric coupling. ( That is the main working principle behind the RFID technology)

Host MCU to PCD

Host MCU will send the commands to PCD, according to which PCD will perform the operations like activation of FIFO buffer or CRC coprocessor, and transmission of data from FIFO. We will name these commands as MFRC522 Commands sets. Host MCU will send those commands to PCD (here MFRC522) by writing into the CommandReg Register using low level Host Interface write API.

  • Idle Command: Places the MFRC522 in Idle mode.
  • Mem Command: Transfers the 25 bytes from the FIFO Buffer to the internal buffer. This command is used when, we want to read the data from PICC( As described in ISO-14443-4 doc), as PICC response is always recorded in PCD FIFO.
  • Generate RandomID: generates a 10-byte random ID number.
  • CalcCRC: Activates the CRC coprocessor or performs a self test.
  • Transmit: transmit data from the FIFO buffer
  • NoCmdChange: no command change, can be used to modify the CommandRef register bits without affecting the command
  • Receive: activates the receiver circuits
  • Transceive: Transmit data from the FIFO buffer to antenna and automatically activates the receiver after transmission.
  • MFAuthent: performs the MIFARE standard authentication as a reader
  • SoftReset: This command performs a reset of the device. The configuration data of the internal buffer remains unchanged. All registers are set to the reset values. This command automatically terminates when finished.


Further there are also command set which PCD have to emit to communicate with PICC and enter the PICC into some state machine.

PICC States:

  1. Power-off State: In the POWER-OFF state, the PICC is not powered by a PCD operating field
  2. Idle State: In the IDLE state, the PICC is powered. It listens for commands and shall recognize REQA and WUPA commands. 
  3. Ready State: Cascade levels are handled inside this state to get the complete UID. PICC enters the ACTIVE state when it is selected with its complete UID.
  4. Active State: PICC complies with ISO-14443-4 to accept protocol activation commands (RATS)
  5. HALT State: In this state PICC only responds to WUPA command.
  6. Protocol State: PICC behaves according to 1s014443-4 specifications.

We will name these commands as PICC commands. Host MCU will write these PICC command into the PCD FIFO (refer the MFRC522 FIFO section on how to write the data on FIFO). PCD would transmit the FIFO data when it enters the Transceiver state machine (refer above topic).

PCD would transmit these commands via the electromagnetic induction and communicates with PICC via electronic coupling. PCD’s have RF transceivers through which it emits the electromagnetic waves with commands sets encoded in them. PICC have antenna and small circuitry, which gets energized via electromagnetic waves emitted by PCD and then further both PCD and PICC get coupled together to have 2 way wireless communication. How PCD would send commands to PICC and in return how PICC would respond, that is done according to IS014443 protocol. ISO14443 specifies all the frame formats,PICC command  and their format ,  modulation schemes for RFID technology. 

PICC Frame formats:

  1. Short Frame:
  2. Standard Frames

PICC Command Set:

  1. REQA/WUPA Command: This command is send by PCD to scan the valid and IS014443 compatible PICC’s.  This command is in short frame format. Host MCU will write this command into the PCD FIFO, from where this command is transmitted and emitted wirelessly. Response to this command is with ATQA. PICC are in Idle state when listening to this command and after successfully transmitting the ATQA response they enter into Ready State. These commands consist of 7 bits, as specified below:
  2. ANTICOLLISION/SELECT Command: PICC are in ready state when listening to this command and after this command they enter into ACTIVE STATE. This Command is used to get the UID of the scanned PICC and further select the corresponding PICC for Reading and writing data from it. For the MF1S503 PICC’s UID is of 4 bytes, for that only 1 cascade level is needed.

These commands need to be configured and then these bytes are written into The PCD FIFO for transmission and emission of signal to PICC wirelessly. This Command consists of:

  • Select code SEL(1byte): Specify the cascade level. 
  • No of valid bits NVB (1 byte): specify number of bytes that would be transmitted by PCD to PICC (including SEL, NVB and below point)
  • 0 to 40 data bits of UID according to value of NVB.

ANTICOLLISION Command consist of:

  1. Select Code: Cascade level 1= 0x93
  2. No of valid bits NVB = 0x20

Response to ANTICOLLISION Command is with the UID of the Scanned PICC(0xEA, 0x24, 0x77, 0x15) and its CRC(0xAC).

  1. SELECT Command consists of:
  • Select code: Cascade level 1 = 0x93
  • No of valid bits NVB – 0x70
  • 0 to 40 data bits of UID that has been received in ANTICOLLISION Command( 0xEA, 0x24, 0x77, 0x15)
  • CRCA(1 byte) : CRC of SELECT Command would be calculated by PCD and then it would be sent to PICC. And When PICC receives the SELECT Command it will check this CRCA and then will send the ACK.(0xAC)

Response to SELECT Command is with the Select Acknowledge:

MFRC522 Hardware and Pinout

MFRC522 IC has 32 pins in total and it comes in SOT617-1 package.

MFRC522 Pinout

Pin description can be found from the datasheet of MFRC522. To use the MFRC522 IC its module is widely available and quite inexpensive. Can be brought from Robu at cost of 150 rupees. With the module an RFID tag and a key fob tag of MIFRAME Classic 1KB comes in.

MFRC522 Module

In MFRC522 module, IC has 8 pins exposed out for connection and connecting to host MCU.

  • The module has 4 pins exposed out for connecting it to host MCU using either SPI, I2C or UART. By default, reader can communicate with a microcontroller over a 4-pin SPI with a maximum data rate of 10 Mbps. It also supports I2C and UART protocols. As told in MFRC522 functional description part, MFRC522 checks the host interface type automatically depending on the signals on it’s control pins.
  • MFRC522 module has 1 interrupt pin also exposed out, which can be used to trigger interrupts to alert the microcontroller when a RFID tag is in the vicinity.
  • And remaining 3 pins are power supply pins and a reset pin. Reset pin is used for power down mode and reset signal. Module requires the power supply of 3.3 V, that is provided via VCC and GND pins.

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