Radio frequency identification (RFID) is an abbreviation for radio frequency identification, that is, identification processing by infinite electric waves. The RFID system usually consists of a reader (reader) and a transponder (card). Its identification data is stored in the transponder circuit. The transponder is a non-contact card. The card itself does not have a power supply. When the card is in the electromagnetic field range of the reader, the power can be obtained by coupling the energy of the radio wave and rectifying and stabilizing. In this way, in the activated state, the data stored on the card can be sent to the reader for identification by encoding and modulation.
Atmel's e5561 circuit is an encrypted radio frequency identification (IDIC) that is suitable for high-confidence applications with an internal encryption unit. Its main performance is as follows:
â— Low power, low voltage CMOS IDIC;
â— Radio frequency (RF) range is 100kHz~150kHz, with a typical value of 125kHz;
â— Contains 320bit EEPROM (in 10 pieces);
â— Bit rate is RF/32, RF/64;
â— The encryption authentication time is less than 10ms;
â— With programmable read / write protection;
â— Adopt Manchester and two-phase coding.
1 Internal structure and working principle
In normal use, the e5561 uses only coil 1 (coil1) and coil 2 (coil2) and external inductors and capacitors, and the remaining pins are not used. Its internal structure block diagram is shown in Figure 1. The chip includes an adaptive part, a pre-module end, a modulator, a decoder, a memory, an encryption circuit, and the like.
When the base station does not match the resonant frequency of the e5561, its adaptive part adjusts the frequency of the e5561 to match the base station frequency, and the adjustment range is 5%. The Preamplifier (AFE) can be used to generate the power required by the circuit while handling bidirectional data communication with the base station.
The memory in the chip is composed of 320-bit EEPROM, divided into 10 blocks, each block of 32 bits; the 0th bit is used to save the basic configuration data, the first block - the 9th block is the user data area, freely programmable, of which 1 -4 blocks are ID codes, and blocks 5-8 are keys. In password mode, 4-31 bits of the 9th block are used to store passwords, and 0-3 bits are used to store user configuration data. Otherwise, block 9 The corresponding bits are also freely programmable.
The programming voltage is provided by a high voltage generator (18V). The encryption circuit AUT64 operates to encrypt the password written to e5561, and the operation result can be read by the base station. Comparing this result with the base station data, a highly secure authentication process can be established.
The modulator consists of two data encoders. The basic modulation types are Manchester and two-phase encoding.
The e5561 can work in the following modes of operation:
(1) ID mode: In the RF field, e5561 cyclically transmits an ID code to the base station. The ID mode allows the use of two different bit rates and modulation schemes, and can use two lengths of ID code generation (64-bit or 128-bit).
(2) Programming mode: The e5561 should be programmed before use. The EEPROM is divided into 10 blocks, each of which is programmed separately, and the data sequence sent by the base station should be written to the EEPROM memory of the e5561. During programming, if the e5561 monitor finds an error or protection is compromised, the system will return to ID mode.
(3) Direct storage mode: When the base station sends a special data sequence to the e5561, the e5561 enters the direct storage mode. This mode has two functions: one is that the base station reads the contents of each block of the EEPROM, and the other is to re-equip the device e5561. During this time, if the e5561 monitor finds an error or the protection is compromised, the system will return to ID mode.
(4) Encryption mode: In this mode, the e5561 uses the AUT64 algorithm (a non-linear, high-security rule). After the base station completes the identification of the e5561 (by reading the ID code), the base station can authenticate the transponder (by sending a password), and upon receiving the data sequence, the e5561 enters the encryption mode. If the e5561 monitor finds an error or the protection is compromised, the system will also return to ID mode.
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