In the development of contactless IC cards, these problems are gradually solved and form a common standard, which is now in the design of RF IC cards, the International Organization for Standardization (ISO) and the International Electrotechnical Commission (IEC). The corresponding international standard for contactless IC cards - ISO/IEC 14443.
The ISO/IEC 14443 standard consists of four parts: the first part of ISO/IEC 14443-1 establishes the physical characteristics of the contactless card; the second part of ISO/IEC 14443-2 establishes the characteristics of the RF power and signal interface; the third part ISO/ IEC14443-3 is the initialization and anti-collision mechanism for contactless cards; the last part of the ISO/IEC14443-4 related transaction agreement. In the second part, the implementation standards of radio frequency technology are introduced, which provides the basis for solving the above problems. According to this standard, there are two types of RF IC cards, Type A and Type B. The main difference is the carrier modulation depth and the encoding of the binary number.
When the Type A card transmits a signal to the card on the reader/writer, it transmits the signal through the 13.65MHz RF carrier. The adoption scheme is a synchronous and improved Miller coding method, which is transmitted through 100% ASK; when the card transmits a signal to the reader/writer, the signal is transmitted through the modulated carrier. The Manchester code is transmitted using a subcarrier of 847 kHz.
The Type B card also transmits the 13.65MHz RF carrier signal when the reader/writer sends a signal to the card, but uses the asynchronous, NRZ encoding method, and transmits it through the 10% ASK. When the signal is used, it is modulated by the BPSK code.
Comparing the two card types, it can be seen that Type B has the following advantages compared with Type A cards:
(1) The chip has higher security. When the signal is received, the internal logic and software operation of the chip are not stopped due to energy loss.
(2) Support higher communication rates. Type A has a maximum data communication rate of 150Kbit/s -200Kbit/s, and Type B with 10% ASK technology can support at least 400Kbit/s.
(3) The peripheral circuit design is simple. The encoding method of reading and writing machine to card and card to reading and writing machine adopts NRZ scheme, the circuit design is symmetrical, and simple UARTS can be used in design.
(4) Strong anti-interference ability. The load wave uses BPSK modulation technology, which reduces the signal sound of 6dB compared to the Type A scheme.
In addition, some differences between Type A and Type B cards have been encountered in the previous anti-collision mechanism. For Type B cards, one-card operation mode and one-multi-card operation mode can be selected according to the actual application.
Depending on the way the signal is transmitted and received, ISO/IEC 14443-3 defines two types of cards, TYPEA and TYPEB. The difference between them is mainly the modulation depth of the carrier and the encoding of the binary number. When transmitting signals from the reader/writer to the card, the two transmit signals through the 13.56Mhz RF carrier.
The TYPEA scheme is a synchronous and improved Miller encoding method, which is transmitted by 100% ASK. Simply put, when the information "1" is indicated, the signal will have a 0.2-0.3 microsecond gap. When the information is "0", the signal may have a gap. It may or may not be related to the information before and after. The advantage of this method is that the information is obviously different, the chance of being interfered is small, the reaction speed is fast, and it is not easy to operate by mistake; the disadvantage is that the energy may fluctuate when the energy needs to be continuously increased to the non-contact card.
The TYPEB scheme is asynchronous, NRZ encoded by transmitting with 10% ASK. That is, the difference between the information "1" and the information "0" is that the signal amplitude of the information "1" is large, that is, the signal is strong, and the signal amplitude of the information "0" is small, that is, the signal is weak. The advantage of this method is continuous signal transmission without energy fluctuations;
When transmitting signals from the card to the reader/writer, both transmit signals through the modulated carrier. TYPEA transmits the Manchester code with a 847 kHz subcarrier. TYPEB transmits signals through 847KHz subcarriers and is modulated by BPSK.
According to the design schemes of the two, it can be seen that TYPEB has the following advantages over TYPEA:
The chip has higher security. When the signal is received, the internal logic and software operation of the chip are not stopped due to energy loss.
Support for higher communication rates. TYPEA's maximum data communication rate is 150Kbit/s-200Kbit/s, and TYPEB with 10% ASK technology can support at least 400Kbit/s.
The peripheral circuit design is simple. The encoding method of reading and writing machine to card and card to reading and writing machine adopts NRZ scheme, the circuit design is symmetrical, and simple UARTS can be used in design.
Strong anti-interference ability. The load wave adopts BPSK modulation technology, which reduces the signal noise of 6dB compared with the TYPEA scheme.
ISO/IEC 14443-3 specifies the anti-collision mechanism for TYPEA, TYPEB. The principles of the two anti-collision mechanisms are completely different. The former is based on the BIT collision detection protocol, while the latter is based on bytes, frames and commands to complete anti-collision. The anti-collision mechanism enables the non-contact IC card to operate in parallel, and after multiple cards enter the effective operation area at the same time, it can be manipulated in an orderly manner, so that the data of the selected card is not interfered by other card data, and carries Users of multiple cards do not have to find the correct card, only algorithm programming, reading and writing tools can automatically select the correct card for subsequent operations. This facilitates the operation, improves the parallelism of the application, and increases the speed of the system.
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