CN103188118B

CN103188118B - A kind of 14443 interface PCD frame end detection methods

Info

Publication number: CN103188118B
Application number: CN201110461136.9A
Authority: CN
Inventors: 高慧; 尹晓杰; 胡毅
Original assignee: Beijing CEC Huada Electronic Design Co Ltd
Current assignee: Beijing CEC Huada Electronic Design Co Ltd
Priority date: 2011-12-30
Filing date: 2011-12-30
Publication date: 2015-08-19
Anticipated expiration: 2031-12-30
Also published as: CN103188118A

Abstract

The invention provides a kind of 14443 interface PCD holds physical layer to cause frame end to detect the processing method of mistake to noise signal.14443 carrier signals, by after radio frequency reception demodulation, amplification, quantification, are delivered to digital decoding circuit and are processed, and the amplitude of noise signal after amplifying then is quantized out after exceeding the threshold level of sample circuit.In order to the false judgment preventing noise signal from causing frame end, the detection adopting the mode of Character mother plate to increase frame end judges the time, thus the probability that raising frame end correctly detects, avoid, after frame end, noise signal is mistaken for useful signal, improve the communication efficiency of interface.

Description

A kind of 14443 interface PCD frame end detection methods

Technical field:

The present invention relates to the detection technique of 14443 interface PCD being held to physical layer Received signal strength frame end.

Background technology:

In contactless smart card field, communication system is divided into read write line (PCD) and card (PICC) two parts.The physical layer signal of PICC end after rf modulations is launched and propagated by air traffic channel, inevitably can introduce Noise and Interference, when these signals are after PCD holds radio demodulating, amplification, quantification, then noise can be introduced digital decoding circuit.Due to the existence of noise, digital decoding circuit can be caused to occur the situation of process by mistake in links such as postamble detections, noise signal is mistaken for useful signal after frame end, or is mistaken for frame end when Signal transmissions, thus causing this time communication to make mistakes, communication efficiency reduces.When operating distance is far away, this problem is especially outstanding, the modulation amplitude of useful signal is little, signal to noise ratio reduces, the amplitude of useful signal and noise has comparativity, ration the power supply to put down by demodulation, filtering or adjustment quantification gate and be all difficult to correctly differentiate useful signal and noise, much noise signal enters digital decoding circuit.

In order to address this problem, need the noise signal treatment mechanism introducing some necessity at frame end detection.Data frame structure generally comprises three parts: start-of-frame (SOF), character (Characters), frame end symbol (EOF), as shown in Figure 1.Wherein frame end symbol is the code shape being different from character of definition separately, and the form of character comprises 1bit logic ' 0 ' start bit, 8bit data and 1bit logic ' 1 ' stop bits, and frame end symbol is the fixed logic ' 0 ' of certain hour.The character masterplate that the present invention utilizes agreement to provide judges frame end, increases the judgement time to improve the correct probability judged, effectively can solve the problem that the correct judgment frame of noise effect terminates.

Summary of the invention:

The invention provides a kind of 14443 interface PCD holds physical layer Received signal strength to detect the method for frame end.

Concrete methods of realizing step is as follows:

(1) when signal is input to digital decoding circuit by radio demodulating, detection signal width, filtered signal width is less than the signal of threshold value th1;

(2) the filtered deration of signal and threshold value th2 are compared, if the deration of signal is less than or equal to this threshold value, then by after data decode stored in character buffer memory, go to step (3); If be greater than threshold value, then go to step (4);

(3) judge whether the data in character buffer memory reach whole byte, if reach whole byte, by the data conversion storage in character buffer memory to data buffer, and empty character buffer memory, if not enough whole byte, circulate and perform step (1)-(3); .

(4) judge whether the data in character buffer memory reach whole byte, if reach whole byte, by the data conversion storage in character buffer memory to data buffer, and empty character buffer memory, if not enough whole byte, be judged as frame end, and empty character buffer memory.

In frame end detection method, need to consider the data-signal change that the deration of signal occurs after radio demodulating to the threshold value th1 of the deration of signal, the setting of th2, leave certain allowance.

Embodiment:

Below in conjunction with accompanying drawing, illustrate the present invention.

Fig. 2 frame end overhaul flow chart is depicted as the process chart causing judging by accident frame end in the present invention to noise signal, according to concrete implementation, comprises the following steps:

Step 201, in filtered signal, width is less than the noise spike of protocol requirement, and consider that useful signal deration of signal after demodulation can change a lot, the filtering threshold of setting needs to leave certain nargin.

Step 202, judges whether the filtered deration of signal is greater than corresponding threshold value, if be not more than corresponding threshold value, then carry out step 203, otherwise performs step 206.In like manner, consider that useful signal deration of signal after demodulation can change a lot, the threshold value of setting needs to leave certain nargin.

Step 203, by after signal decoding stored in character buffer memory.

Step 204, judges whether the data bit number in character buffer memory equals 8, if equal 8, then carry out step 205, otherwise circulation performs step 201 to step 204.

Step 205, by whole character 8bit data stored in data buffer, empties character buffer memory simultaneously.

Step 206, judges whether the data bit number in character buffer memory equals 8, if equal 8, then carry out step 205, otherwise performs step 207.

Step 207, is judged as frame end, empties character buffer memory simultaneously.

Should be understood that, the present embodiment is used for illustrative purposes only, but not limitation of the present invention.Person skilled in the relevant technique, without departing from the spirit and scope of the present invention, can also make various conversion or change, and therefore all equivalent technical schemes also should belong to category of the present invention by each claim.

Accompanying drawing illustrates:

The frame end form that Fig. 1 is desirable and the actual frame end form comprising noise

Fig. 2 frame end overhaul flow chart

Claims

1. 14443 interface read write line PCD hold physical layer Received signal strength to detect a method for frame end, it is characterized in that step is as follows:

(2) the filtered deration of signal and threshold value th2 are compared, if the deration of signal is less than or equal to this threshold value, then by after data decode stored in character buffer memory; If be greater than threshold value, then go to step (4);

(3) judge whether the data in character buffer memory reach whole byte, if reach whole byte, by the data conversion storage in character buffer memory to data buffer, and empty character buffer memory, if not enough whole byte, circulate and perform step (1)-(3);