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Circuit for decoding type A signals sent by card reader based on ISO/IEC 14443 protocol

A decoder and card reader technology, applied in the direction of instruments, inductive record carriers, computer components, etc., can solve the problem that the carrier clock cannot be recovered from the carrier wave

Active Publication Date: 2016-01-06
SHANGHAI HUAHONG INTEGRATED CIRCUIT
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Due to the different modulation degrees, when receiving the low level of the type B signal, the carrier clock can be recovered from the carrier; when receiving the low level of the type A signal, the carrier clock cannot be recovered from the carrier due to the 100% amplitude modulation

Method used

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  • Circuit for decoding type A signals sent by card reader based on ISO/IEC 14443 protocol
  • Circuit for decoding type A signals sent by card reader based on ISO/IEC 14443 protocol
  • Circuit for decoding type A signals sent by card reader based on ISO/IEC 14443 protocol

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Embodiment Construction

[0015] combine Figure 4 As shown, the decoding principle of the main decoder circuit of the circuit of the type A signal sent by the card reader in the decoding ISO / IEC14443 protocol is as follows:

[0016] From Figure 1~3 , it can be clearly seen that the Z waveform is followed by the X waveform, the Y waveform, and the length of the high level between the two low levels corresponding to the Z waveform is different. Further explanation, if there is a high level less than T / 2 after the Z waveform, then the X waveform is followed by the Z waveform; if there is a high level greater than T / 2 and less than T after the Z waveform, then the Z waveform is followed by The Z waveform is the Z waveform; if the recorded high level is greater than T before receiving the next low level after the Z waveform, then the Z waveform is followed by the Y waveform. By analogy, the subsequent waveform can be judged from the previously determined waveform and the length of the high level between ...

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Abstract

The invention discloses a circuit for decoding type A signals sent by a card reader based on the ISO / IEC 14443 protocol. The circuit comprises a master decoder circuit used for recording the length of a high level between two low levels of envelop signals after the analog demodulation treatment, and decoding type A signals according to the length of the high level between different code words defined in the ISO / IEC 14443 protocol; a reception signal type judging circuit connected with the master decoder circuit and used for recording the number of clocks contained in envelop signals during the low-level period after the analog demodulation treatment, and comparing the recorded number of clocks with a preset threshold at the end of the low-level period. When the recorded number of clocks is larger than the preset threshold, the reception signal type judging circuit sends out a marking signal to drive the master decoder circuit to ignore low-level signals. According to the technical scheme of the invention, whether a card reader sends out type A signals or type B signals can be correctly found out. During the decoding process of type A signals, the influence of type B signals is shielded.

Description

technical field [0001] The invention relates to an improved circuit for decoding type A signal sent by a card reader in the ISO / IEC14443 protocol. Background technique [0002] There are two types of signals in the ISO / IEC14443 protocol, called Type A signals and Type B signals respectively. The waveform of the type A signal is a 100% amplitude modulated modified Miller signal (ASK100%ModifiedMiller). It corresponds to three types of waveforms according to different code words, which are called X, Y and Z waveforms respectively. For the waveform diagram, see Figure 1~3 shown. Figure 1-3 T in represents the duration of a codeword, and W represents the duration of the low level. T and W have corresponding specified values ​​in the ISO / IEC14443 protocol according to different transmission data rates. [0003] The coding rules stipulated in the ISO / IEC14443 protocol determine that the Z waveform must be sent first. The waveform of the Type A signal is a ten percent amplitu...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): G06K7/00
Inventor 王吉健
Owner SHANGHAI HUAHONG INTEGRATED CIRCUIT
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