An RFID application in embedded systems

Introduction RadioFrequency IDentification Contactless – radio subject identification Fast, efficient and reliable method of identification Commonly used in:- automotive industry (key transponders)- access control systems- public transport ticketing- asset management- ePassports etc.

Hardware architecture of the RFID electronic lockElectrical schematic

Hardware architecture of the RFID electronic lockRFID module RFID operates on the following standard frequency carriers:▪ Low-Frequency (LF) [125 KHz – 139 KHz] ISO14443A/B▪ High-Frequency (HF) [13.56 MHz] ISO14443A/B,ISO15693▪ Ultra-High-Frequency (UHF) [433 – 960 MHz]▪ Microwave [2.45 GHz +] The operating distance of the RFID module is directly proportional to thefrequency carrier; higher reading range is achieved on higher frequencies Low-Frequency RFID modules are less sensitive to metal objects in thesurroundings compared to higher frequency RFID modules Higher operating frequency though provides a larger data throughput andtherefore a faster identification of the subjects.

Hardware architecture of the RFID electronic lockRFID module Mediator between the microcontroller and the RFID usercards Provides the wireless communication link, (de)coding,(de)modulation of the data being exchanged between themicrocontroller and the contactless RFID cards Operating carrier frequency f C =13.56 MHz Operating distance od 7cm achieved Compliant to the ISO14443A standard Why was 13.56 MHz chosen as the carrier frequency?- RFID cards can be read at a maximum 10cm distance from the reader, which is ideal for an accesscontrol system.- The module’s antenna requires much less loops compared to LF readers’ antennas- Relatively fast data exhcange between the module and the card- RFID cards/transponders intended for 13.56MHz operating frequency commonly have a largermemory capacity which allows a larger user flexibility

Hardware architecture of the RFID electronic lockRFID modulePrinted Circuit Board Design Drawn in Proteus(ARES) v7.2 Manufactured in Hitech– Macedonia based onthe generated Gerberfiles Integrated PCB antennamade up of 4 turnsFront side viewBack side view

Hardware architecture of the RFID electronic lockCLRC632 RFID IC Basic element of the RFID module Made by NXP Semiconductors Supports ISO14443A/B, ISO15693, ICODE Completely integrated concept of (de)modulation,(de)coding, parity and error control and data verification Internal 512B EEPROM memory 64 internal 8-bit registers Digital, analog and radiofrequency section Allows integration of an antenna with a minimum number ofexternal passive components SPI communication with the microcontroller LPC2148

Hardware architecture of the RFID electronic lockSPI interface(Microcontroller LPC2148) SPI controller with internal configuration registers MASTER mode of operation 16-bit bidirectional shift data registerLPC2148SCK0MOSI0MISO0GPIO0.20SCKMOSIMISOSSEL

Hardware architecture of the RFID electronic lockSPI interface(RFID module – CLRC632 RFID IC) Automatic interface detection (SPI or parallel) A maximum data rate of 5 Mbps SLAVE mode of operation Has its own predefined protocols for writing and reading theinternal registers of the CLRC632CLRC632SCKMOSIMISOSSELA2A0D0ALE

Hardware architecture of the RFID electronic lockCLRC632’s SPI protocols(RFID module – CLRC632 RFID IC) The microcontroller initializes the SPI comunnication bysending two bytes 0x00 to the CLRC632. Writing into the CLRC632 registers Reading the CLRC632 registers

Hardware architecture of the RFID electronic lockRFID cards Mifare 1k Classic (NXP Mifare технологија) Compliant to the ISO14443A standard A passive RFID transponder, f C = 13.56 MHz Maximum operating distance is specified at 10cm Internal 1kB EEPROM memory Unique 32-bit idenfitication number (Unique IDentifier) Supports NXP’s Crypto algorithm for safe transactions

Hardware architecture of the RFID electronic lockInternal structure of the card

Hardware architecture of the RFID electronic lockPhysical layer Coding and modulation (RFID module)- Modified Miller coding- 100% ASK modulation

Hardware architecture of the RFID electronic lockPhysical layer Coding and modulation (RFID card)- Manchester coding- Load modulation (using a sub-carrier at 847.5 kHz)

Hardware architecture of the RFID electronic lockPhysical layer Inductive coupling (K ~ 0.3) Wireless power transmission

Hardware architecture of the RFID electronic lockA block diagram of the card’slogical statesREQ- A request for opening acommunication link with anexisting RFID card in thereader’s fieldSEL + NVB- A command sent to thedetected RFID card in orderto read the full UID numberPOWER OFFIDLEREADYACTIVEPOWER OFFAfter 5 ms in the RFID reader’s field a card ispowered and ready to communicateCommand: REQ (0x26)Transition: IDLE - READYCommand: SEL (0x93) + NVB (0x20)Transition: READY - ACTIVEThe RFID reader shuts down the RF field afterreading the UID number

Hardware architecture of the RFID electronic lockData layer of the RF linkRFID moduleREQ (0x26h)REQ (0x26h)REQ (0x26h)SEL (0x93h)NVB (0x20h)RF wireless linkRFID cardA card was detected!ATQ (0x04h)UID Byte 0UID Byte 1UID Byte 2UID Byte 3

Software architectureof the RFID electronic lock The program code is written in embedded C, the IAREmbedded Workbench 5.0 IDE was used Main features:- Periodical interrogation of cards in order to save energy- Simple and easy to program new or delete existing cardsfrom the microcontroller flash database by presenting apredefined PROG or DEL card to the reader accordingly- Timestamp and logging of the complete activity of theRFID lock in a .txt file placed in an SD card (1GB) in order toretrieve vital access control information later on- Flexible database management, can be stored in internalflash of the microcontroller or based on a removable SD card

Software architectureof the RFID electronic lock An overview of the procedures in the code:- void ScanCard()- int CardType()- void ProgrammingCard()- void DeletingCard()- void VerifyCard()- void TimeStamp()- void Signalize(int SignalType)

Software architecture of the RFID electronic lockBasic flowchart

Software architecture of the RFID electronic lock Procedure for programming new cards into the database(PROG card)

Software architecture of the RFID electronic lockProcedure for deleting existing cards from the database whenthe DEL card is detected in the reader’s field

Software architecture of the RFID electronic lock Procedure which determines the card type (USER, PROG orDEL)

Software architecture of the RFID electronic lock Procedure for checking the privileges of the shown RFID cardand decision of accessvoid VerifyCard()Процедура за проверка даликартичката е овластена запристап до просторијатаDoes the card exist in thedatabase?yesSignalize(CARD_ACCEPTED)noSignalize(CARD_DENIED)EXITUnlock the door with a 3 seconddurationLock the doorEXIT

Software architecture of the RFID electronic lock Procedure for reading the UID number from the RFID card

Possible upgrades Introducing an ethernet link to a local or remote server whichwould manage a whole system of interconnected RFID locks Voice or visual notification of the access status (cardaccepted/denied/programmed/deleted etc) Storing lock-specific data into the user’s RFID card internalEEPROM memory for greater flexibility and options Increase the operating distance (?) Visual C based software for managing the lock’s databasesand logs on a personal computer