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  AVR Applications
AVR 자료실
작성자 leeky        
작성일 2006/12/27
Link#1 (Down:50)
ㆍ추천: 0  ㆍ조회: 858   
  ATmega16 RFID #1 태그
◎ 개요(abstract)
이 자료는 RFID 읽기-쓰기 장치의 하드웨어와 소프트웨어를 설명한다.
이것은 응용과 함께 읽기-쓰기 작동원리의 검토를 포함하여 RFID 공학을 새롭게 소개한다.
다른 중요한 요점들은 다음의 제목으로 표시된 부제안에 게재되고 설명되었다.    
.
자료는 깊이 있는 이 문서로 RFID 지식과 가장 표준적인 문제들을 해결하려는 누구에게나 제공된다.  
매우 좋은 전자 기본지식과 프로그램의 경험은 충분히 제목안의 모든것을 알도수 있도록 도움을 줄 것이다.
자료는 PDA 같은 외부의 휴대 컴퓨터에서 장치의 읽기-쓰기를 쉽게하는 Java Micro Edition API를 소개한다. 

◎ 과제의 설명
이 자료는 RFID ToolBox라는 각종의 무접점 정보수집 장치에 사용할 수 있는 RFID 읽기/쓰기 장치를 제공한다.  
장치는 RFID 기술로 front-end를 만드는 Sokymat IC와 통신하는 Atmega16L AVR MPU 기반으로 설계되었다.
RFID 장치는 송수신기와 전송기(transponder) 혹은 tag, 안테나 혹은 코일로 이루어져 있다.
읽거나 쓰는 tag가 허용하는 무선신호는 안테나 작동으로 방사된다. RFID ToolBOX는 휴대형 컴퓨터로 통신한다.
Device is capable of reading information stored on transponders and present results
to user in human readable form.
The project development consists of several stages.
First was PCB board design together with elements selection.
Next step was a software design and implementation in a meaning of protocols,
API and functional application.
.
RFID ToolBOX can offer new kind of functionality yet not present on the market.
There exists mobile tag readers offered by almost each manufacturer,
but they all have common drawback, data gathered can't be immediately sent to remote location.
Proposed device has such feature,
.
what can be widely used in token passing for cryptography purposes or digital signing.
Of course it can work as ordinary reader, but possibility of sending data to remote
location immediately after reading gives it a major advantage.
Small size and almost weightless box, attached to mobile device gives a very handy solution.
.
Three most common transponder types are supported: Sokymat UNIQUE – Read Only,
Sokymat Q5 – Read/Write and other manufactures tags (MicroChip, Atmel),
keeping well defined memory organisation.
.
그림 1의 구성도는 RFID Tool-Box의 작동원리를 설명한다.
 
1. RFID의 소개
RFID 표준
필립스는 금년에 Hitag로 그들의 RF장치를 개발하고 소개하고 있다,
Texas Instruments에서 RFID 장치 같은 주요 생산품은 시장에서 안정된 위치이다,  
거의 대부분, 그들은 새로운 표준을 필요로 하지 않는다.
.
국제 위원회는 Philips, TI, Hitachi, Siemens, Sokymat, Swatch-Marin, Atmel 에서
철저하게 토의한 해결방안을 고려한 표준을 소개하였다.  ISO 실지 표준을 따르지 않는,
일반적으로 현재의 중요한 제작사의 해결방법(solution)은 없다.  
.
◎ 응용별 반송파 주파수대역(frequency division)
그림은 사용된 Tag의 반송파 주파수에 따르는 RFID의 응용을 제공한다.
EAS는 전자 물품 감시용, ISM은 산업, 과학과 의료용의 약자이다.
 

◎ 분류 표준
그림은 SC31 분과 위원회와 RF Tag 표준의 WG4 Group을 뿌리로 ISO 표준분류 조직을 보여준다
 
 
1.4 고주파 작동 원리
Few questions can arise. How the tag is powered?
Is it intelligent enough to know when to transmit stored data? Here comes the answer.
The tag is activated by a radio signal with pre-set frequency and sends a signal in return.
Returning signal contain desirable information in form of unique identification number or other data.
Electromagnetic wave sent from interrogator gives power to wake up the tag,
power it's internal circuits and give energy to transmit data.
.
Information exchange is done via air interface, precisely through electromagnetic waves,
so without physical contact with reader.
Readers and tags communicate using low power radio frequency (RF) signals.
.
An RFID system consists of an antenna or coil, a transceiver and a transponder (tag).
A radio signal emitted by the antenna activates the tag allowing it to be read
and in some instances have data written to it.
Antennas are also available in a wide variety of shapes and sizes to suite specific applications.
They can be mounted under a road surface to monitor vehicle access through a given point
or they can be packages together with a transceiver to become a reader.
.
A reader can be either hand-held like the subject of diploma work
or can be mounted as a fixed device for access control purposes.
The antenna within a reader emits radio waves ranging anywhere
from 2.5 centimetres to about 2 meters,
depending on its power output and the radio frequency used.
.
The tag passing through this electromagnetic field detects activation signal
and the reader decodes the tag's encoded data and passes it on to
the host computer or information management for system processing.
.
Very important is to understand bit rate (data rate) concept. Most typical bitrate
values in [bit/s] are RF/8, RF/16, RF/32, RF/40, RF/50, RF/64, RF/80, RF/100, RF/128.
Every tag sends back information with some predefined, usually fixed bit rate.
Once manufacturer programs the data rate, it cannot be changed.
This data rate is clocked by internal tag frequency.
For Low Frequency (LF) transponders it is a range from 100kHz to 150kHz, depending on manufacturer.
Taking for example transponder type that bit rate is RF/32.
It means that data rate is 32 Field Clocks (abbreviation FC) per logic '1' or '0' data bit.
.
Look at Figure 1.4.a. TOC is a period of field clocks.
Data (bit) rate is a bit time duration and it is defined as field clocks per bit.
Taking field clock equal to 125kHz and tag bit rate equal to RF/32 data rate is 125 kHz/32 =3.9062 kBit/s,
so receiving 64 bits of information would take 8μs*32*64=16.384ms.
Tags can use different modulation methods to avoid errors while transmitting the information.
This is more deeply explained in section 2.2, see Figure 2.2.a
.
그림 1.4.a. 비트속도 설명
  

2. 하드웨어 배경
2.1 Tag 종류 훑어보기(review)
Tag types can appear on the market in variety of forms, sizes and shapes. Key-holder
(Tear Shape), Wristband, World Tag, Glass Tag, Nail tag (timber tagging), ISO Cards (credit card size),
Clamshell Cards, Button (pill type) Tag and other like special tags for freight containers marking.
.
Tags can be programmed by manufacturers to operate in many standards.
Refer to section 2.2 for more deep coverage.
Also code lengths received form transponders varies in a range form 32, 64, 96, 128
bits in most typical applications to hundreds of bits like 256, 330, 1000 etc.
.
Transponder types concerned in project use Manchester coding. In Manchester coding
scheme there is always a transition from ON to OFF or from OFF to ON in the middle of bit period.
At the transition from logic bit “1” to logic bit “0” or logic bit “0” to logic bit “1” the
phase change. High data value in data stream below shows modulator switch OFF, low
represents switch ON, look at figure 2.1.a. as an example.
.
그림 2.1.a. Manchester 코딩의 예
 
 
Active RFID tags are powered by means of a battery, either internal or from another
source such as the battery of a vehicle. This battery-supplied power generally gives the tag a
greater read range although the tag is usually larger in size and more expensive. A typical
scenario for the use of active RF tags is the control of vehicles through a specified access
point. As the tagged vehicle approaches the access point, receiver decodes the tag and the
authorized vehicle is allowed access by means of a gate or boom.
.
A passive tag gains its power from that generated by the reader and has no internal power source.
This type of tag is therefore less expensive and is smaller and lighter than the active tag.
It also offers a virtually unlimited operational lifetime.
Their read range is however shorter and they need to be activated by a higher-powered reader.
.
그림2.2 Tag에 사용된 변조의 종류
Figure 2.2.a shows most typically used types of coding that transponders are able to produce.
The diagram serves as outlooks just to familiarize reader of publication
with possible coding combinations and get overall idea how they differ.
.
주파수(FSK) 변조
Logical data “1” and “0” are represented as two different frequencies of damping.
The frequency for “1” is for example RF divided by 10,
a “0” divides RF by 8 or different depending on manufacturer.
For example RF/40 (MOD40), gives 4 sets of 10 RF carrier cycles for data ‘1’
and 5 sets of 8 RF carrier cycles for data ‘0’.
.
위상(PSK) 변조
The external coil is for example damped with a carrier frequency of RF/2.
A logical “1”causes (at the end of the bit period) a 180°phase shift on
the carrier frequency, while a logical “0” causes no phase shift.
.
2상(Biphase) 변조 (Biphase S)
Logical “1” produces a signal which is the same as the internal bitclock.
A logical “0”produces no signal change in the middle of the bit period.
.
반전(Manchester) 변조 (Biphase L)
A logical “1” causes a rising edge in the middle of a bit period (i.e., switch damping off),
while a logical “0” causes a falling edge (i.e., switch damping on).
.
그림 2.2.a. 변조 옵션을 위한 Timing
 

2.3 지원되는 전송기(Transponders)의 설명
2.3.1 Sokymat UNIQUE
Tag that appears on the market, as Sokymat UNIQUE, is a contactless power supply,
64 bits Read Only transponder for 125kHz range applications. Many other manufacturers
have identical in their offer. Transponders are the same with respect to capacity, transmission
speed and modulation used. Following description is based on Sokymat product because tags
by this producer are used as samples in diploma project and were tested by genuine reader.
.
Sokymat Unique Typical operating frequency is 125kHz. Capacity is 64 bits of Read Only memory.
Data rate can be chosen from 2, 4 or 8kbd and coding type can be chosen from Manchester, Biphase or PSK.
As this kind of tag is read-only, pre-sets of data rate and coding type are made during device manufacturing.
.
그림 2.3.1.a. Unique 메모리 배치
 
 
Standard Sokymat configuration is Manchester, 2kBd.
Manufacturer can of course produce for given customer tag that will have
for example 8kbd and PSK coding,
 
but such orders are executed if number of tags exceeds 1000 pcs.
Also manufacturer quarantines the uniqueness of the codes for the series he produce.
On customer request, special Customer ID codes can also be programmed
in and in such situation uniqueness of codes can be violated.

Once the incoming RF field is detected, the IC continuously transmits the
identification code as long as the RF signal is applied. For the Sokymat Unique the
identification code, data stored on tag, is in form depicted on Figure 2.3.1.a.
.
Transmission starts with 9 header bits (all programmed by manufacturer to “1”).
The sequence of nine “1” bits, plus the stop bit allows the message synchronisation
and cannot be reproduced in the data string. Stop bit is programmed to "0".
 
 In other words, sequence of data programmed into tag should differ from pattern:
nine one's and one zero.
 
These first nine bits of "1" can be called a transmission header.
For Sokymat this is nine times "1", while other manufacturers can use different value,
for example Atmel e5530 starts with header byte value of E6 hex (’1110 0110’)
and then 56 data bits are transmitted giving total of 64 bits.

Coming back to Sokymat Unique, just after header bits,
four bits (D00...D03) of customer ID plus line even parity bit P0 is transmitted.
Then the rest of customer ID bits plus proper line parity bits are transmitted.
.
In general 10 groups of four data bits plus one line parity bit after each group is
transmitted, allowing more than 232 combinations. IC generates line even parity bits, they are
not programmed as a user data. After 32 data bits alternated with 8 parity bits sequence, IC
transmits last portion of data. Four column even parity bits (C0...C3) and 1 stop bit
programmed to “0” finishes the transmission.
.
2.3.2 Sokymat Q5
The Q5 by Sokymat is a contactless power supply, Read/Write transponder for
applications in the 125-kHz frequency range. This IC is much more complicated than Unique
type. Total capacity is 256bits EEPROM memory, 8 words of 32 bits can be written freely by
user, giving total of 224 bits of user memory including optional 32 bits password block to
prevent unauthorised tag access. The difference between 256 and 224 bits originates from a
32 bits long, Q5 configuration register.
.
Similarly to Unique, data rate and return transmission modulation type can be set.
Standard Sokymat configuration is Manchester coding and 2kBd data rate (to resemble
Unique code like). But Q5 gives a user a possibility to select these options freely.
 
By writing to special configuration register, tag user has an opportunity to change data bit rate
in range from 1 to 62kBd and switch modulation type between FSK (2 different),
Manchester, Biphase, PSK (3 different) or NRZ.
 
The data rate is binary programmable to operate at any bit rate between RF/2 2
and RF/128, but a common multiple of bitrate and FSK frequencies is strongly recommended.
.
Bit 0 of every block is the lock bit for that block (L on Figure 2.3.2.a). Once locked,
the block (including the lock bit itself) is not re-programmable through the RF field again.
Only reading of this block is allowed, no further writings will be possible.
 
Block 0 contains the mode/configuration data, which is not transmitted during normal read operation.
Block 7 may be used as a password, in such case user has only six blocks to take advantage of.
.
그림 2.3.2.a. Sokymat Q5 메모리 배치
 
 
The Q5 has many interesting additional features like: Write protection command to
lock the words independently one from another, Password Mode to allow reading or writing
one word after password check, also Answer On Request that silence the modulation of
transponder in the field on Request only.
.
All these extra features, described thoroughly on following pages, causes that Q5 is
very attractive for multiple purposes, reliable (EEPROM data retention is typically 20 years,
tested for minimum 100,000 programming cycles) and relatively cheap (~1$) in comparison
with possibilities.
.
Tag 초기화
Power–On–Reset circuit (POR) remains active until an adequate voltage threshold has
been reached. This in turn triggers the default start–up delay sequence. During this period of
128 field clock cycles (FC) the transponder is initialised with the configuration data stored in
EEPROM block 0. During initialisation of the configuration block, modulation is switched
off. Any field gap during the initialisation time of typically 2.5 ms will restart the complete
sequence. After this initialisation time the ASIC enters read mode and modulation starts
automatically using the parameters defined in the configuration block. Refer to Figure 2.3.2.b.
.
그림 2.3.2.b. POR 이후의 코일의 전압
 
2.3.2.1 Q5 특별 규격
Normal read mode
Every time the tag enters in the field, it starts modulating automatically in normal read
mode, except if the Answer-on-Request is set. AOR is a special function discussed later in
this chapter.
.
Every time entering reading mode, the first bit transmitted (start bit) is a “0”. The data stream
starts with block 1, bit 1, continues through MAXBLOCK bit 32 and cycles continuously
until the next command or field switch off occur (Figure 2.3.2.1.a).
.
Access 2.3.2.1.a. Q5 송신
 
 
최대 블록 규격
The user may limit the cyclic data stream by setting the MAXBLK between 0 and 7
(representing each of the 8 data blocks). In other words this option defines the number of
readable blocks. If set to zero, the contents of the configuration block – normally not
transmitted – can be read. If set to 1, only block 1 is read. If set to 7, blocks 1 through 7 can
be read. Look at example on Figure 2.3.2.1.b with MAXBLK set to 2. 
 
직접 호출(Access) 명령
Direct Access Mode allows reading one word without check of password. With the
direct access command only the addressed block is repetitively read. Direct access is entered
by transmitting the write opcode '10', a single ‘0’ bit and the requested 3 bit block address.
.
초기화 모드(mode)
With the command opcode '00', it is possible to reset the tag. After data access time, it
restarts modulating in normal read mode. This command can be used for synchronisation
purposes (그림 2.3.2.1.c).
.
그림 2.3.2.1.c. 초기화(Reset) 모드 - 읽기의 동기화
 
 
요청 모드(mode)에서의 응답
When the Answer on request (AOR) bit is set, the Q5 does not start modulation in the
read mode after loading of configuration block 0. It waits for a valid “Wake up command”
from the reader before modulation is enabled. This command consists of an opcode '10'
followed by the valid password. If the password sent matches that stored on tag, after data
access time, Q5 starts modulating in normal read mode (Figure 2.3.2.1.d, e) and remains
active until the RF field is turned off or a new command with a different password is received.
.
AOR is an excellent example how to cope with tag collisions during reading process.
Only one tag is answering at a time, no electromagnetic field collisions occur and reader
receives trustworthy data. AOR wakeup sequence time duration is from 8.7 to 20ms
.
그림 2.3.2.1.d. AOR 모드(mode)
 
 
암호 모드 - Security strength
When password mode is activated (use PWD = 1), the first 32 bits after the opcode are
regarded as the password. They are compared bit–by–bit with the contents of block 7, starting at bit 1.
.
If the use PWD bit is zero, the Q5 accepts any bit stream containing 32 data bits in
place of a password and will enter programming mode. In password mode, MAXBLK should
be set to a value below 7 to prevent the password from being transmitted by the Q5.
Every transmission of the two opcode bits, 32 bits for a password, plus 3 address bits
(= 37 bits) needs about 10 ms. Trying to hack the password is impossible. This activity
require testing all 232 possible combinations (about 4.3 billion) which would take over
one/two years using fast/normal write method!
.
2.3.2.2 쓰기 처리
Optimal 쓰기 timing 설정(setup)
Data send to the Q5 consists of a serial data stream. Each bit send is represented by a
gap (no Field Clocks -FC) followed by a number of FC equal to a “0” or “1”. A data stream is
terminated, the Q5 exits the downlink mode, when more than 64 field clocks are detected after
a gap. The clock counts within 64 clocks are divided into two valid ranges (normal and fast
write mode) for “0” and “1” as shown in Table 2.3.2.2.a. Programming starts if the correct
number of bits were received. If there is a gap failure – the Q5 IC does not start programming,
instead it will enter uplink mode beginning with block 1, bit 1.
.
The length of the start gap Sgap can be between 10 and 50 “virtual” FC.
Virtual, because no FC are present during a gap.
The length of a write gap can be chosen between 8 and 20 “virtual” FC.
Refer to Figure 2.3.2.2.a. The duration of the gaps is usually equal to 14 field clocks.
In normal write mode the time between two gaps is nominally 24 field clocks for
a ”0” and 56 field clocks for a ”1”.
.
In the optional fast write mode the time between two gaps is nominally 12 field clocks
for a ”0” and 28 field clocks for a ”1”.
If there is no gap for more than 32 field clocks after a previous gap, the Q5 will exit the downlink mode.
.
표 2.3.2.2.a. Q5 쓰기 timings
 
 
 
Because of the nature of a tag as resonant circuitry it is
with no doubt necessary to take the ringing of the coil into account.
Having this in mind it is obvious, that the gap length must be long enough,
so that the tag can settle to zero oscillation, when the field is switched off.
For this reason the gap length should be at the upper bound, when searching for write timing.

In general it can be assumed that an air coil corresponds to the low Q family (a Q factor below 15)
and the following settings are recommended.
Gap length equals to 20 FC and because of the coil ringing, the clock count
for “0” and “1” should be at the lower bound: 17 FC for “0” and 49 FC for “1”.
.
데이터 쓰기
Typical programming time is 5.7 ms.
This cycle includes a data verification read to grant secure and correct programming.
After programming is done, the Q5 enters read mode, with the block just programmed.
The data bits are read in the same order as written.
          


 The Q5 always expects to receive a dual bit write op-code first. Writing has to follow these rules:
-– Standard writing needs the opcode, the lock bit, the 32 data bits and the 3 bit address (38 bits total).
 
표준 38 비트 쓰기 (PWD = 0)
 


-– Writing with usePWD set requires a valid 32 bit password between opcode
   and the address/databits Password write 70 bits (usePWD = 1)

 
- In AOR mode – with usePWD set – opcode and a valid password are necessary to
  enable modulation. AOR request 34 bits (usePWD = 1) 
 

 
표 2.3.2.2.b 작동 모드(Mode)
 
 
 그림 2.3.2.2.b.는 완전한 쓰기 순서이다
 

.
그림 2.3.2.2.c. Block 0 설정(configuration) 배치도(map) 


2.3.3 다른 호환 전송기(transponder) 종류
Presented Reader/Writer device got practically unlimited compatibility possibilities looking form hardware point of view.
Reading of different tag types, independent on manufacturer, is possible.
Sokymat Tag Reader IC used in project stands as front-end between
microprocessor and various transponders to be read.
All necessary functionality is built in this IC (more detailed description is in Sokymat Tag Reader IC section)
and for more demanding users there is a possibility to choose HTRC1100 by Philips instead of Sokymat IC.
These both Readers are dedicated to work within 125kHz range (LF3 transponders),
both can handle with different coding and modulations.
For these reason there is almost no limitation from hardware side of project.
For sure it won't handle cryptographic transponders and that working at carrier frequencies above 150kHz.
.
The key of compatibility lies beyond the firmware implemented in microprocessor.
Firmware must handle specific type tags behaviour, keeping for example special timing
considerations while writing or interpret properly captured data, while reading.
It is up to the constructor or just end-user to upgrade firmware for specific tags handling.
According to author's knowledge about RFID and technical specifications of other commonly available tag's,
incomplete list of device-compatible transponders (assuming proper firmware changes) is below.
.
Firstly, products similar to Sokymat Q5 like Sokymat Titan R/W Transponder with 1kB user data.
Also Marin-Swatch P4150 as an equivalent to Titan tag type can be compatible with reader.
.
All products starting with symbol H4xxx like H4005, H4105, and H4102 by different manufacturers.
These all are read Only, LF transponders with 64, 96 and 128-bits user memory,
ISO11784/11785 compliant, powered by means of externally connected coil (antenna).
그림 2.3.3.a을 참조하라.
.
All transponders following the FDX-B ISO Specification, which is defined as follows: Modulation = ASK,
Data encoding = Differential Biphase, Baud rate = RF/32 = 4 kbits/sec for 128 kHz, Memory size = 128 bits.
Also Atmel e5530, HITAG1 (Read/Write, 2k bits with memory area protection feature)
and HITAG2 (Read/Write, 256 bits) both are well known Philips standard.
Also Tiris tags by Texas Instruments can be read by presented Reader/Writer device.
Look at figure 2.3.3.b. and compare it with 2.3.3.a. to see how data formats can differ and how much depends
on firmware responsible for proper data decoding.
.
그림 2.3.3.a. H4102, H4005, H4105 tag의 메모리 배치

 
그림 2.3.3.b. Tiris 데이터 구조(Format)
 

2.4 충돌 문제
Firstly Sokymat Tag Reader IC doesn't support any kind of anti-collisions support.
It's up to firmware to analyse if received data is not spoiled.
Analysis can be done basing on information about coding type and data bit rate.
Let's take for example Manchester coding, here it is very easy to detect corrupted data.
No state '0' nor '1' can lasts more than one bit length
(bit length is RF/x, where x can be 64, 32, 4 depending on tag type).

User of the Reader can only be signalised about situation and it's up to him to retry
reading process once again, eliminating if possible the source of disruption.
As far as Application Notes information can be trustworthy,
also Philips Reader/Writer HTRC1100 chip doesn't have any anti-collision mechanism built in.
.
2.4.1 다른 해법
Certain tag tapes producers introduce Answer-on-Request feature for collision problems solve.
An AOR from Sokymat Q5 is an excellent example how to silent all transponders except one,
with valid password, from the group of being inspected.
Firstly, tags must be specially pre-programmed to be in AOR mode.
The only inconvenience is password knowledge of certain transponder to begin communication with them.
Here comes the conclusion that it is not a true anti-collision capability.
In most of real life situations, the reader device doesn't know anything at all about transponders inspecting. 

On the other hand, the easiest solution is that, user or designer of RFID system can predict collision situations
and decide to use special tags that use different anti-collision solution.
Possibility of real anti-collision gives Microchip with its MCRF250 tags [5] with mechanism of different reaction times.
The tag does not output data until it sees the first RF gap (no RF field for about 60 μsec).
.
When the device sees the first gap, the internal random number oscillator starts clocking immediately after the gap.
At the same time, the internal random number counter starts counting the random clocks number.
The transponder waits for 5 bit times (about 5 msec for MOD128 configuration).

Example: 1 bit time=RF/128=1 msec for 128 kHz for MOD128.
After the 5 bit times, the device sends data. At this time, the random number counter is still running.
If multiple tags in the field send data at the same time, the reader will see a data collision.
If it happens reader must try once again reading process by sending second gap pulse.
Random number generators will generate new, different time lags and there is a chance of success.
.
As a result each device will output data
in different time frames since each random number counter will arrive at ‘0’ at different time.
The reader can receive unspoiled data from a different tag in each time frame
.
Time slotted system is a way to fight with collisions.
After the reader has sent its request to the tags, it waits a certain amount of time for their answers.
This time frame is divided into a number of slots that can be occupied by tags and used for sending their answers.
Time slots lengths are of special size calculated basing on data rate speed and capacity of tag.
When multiple tags use the same slot, a collision occurs and data gets lost.

The reader can vary the frame size, e.g. for maximising throughput;
the actual size of a slot is chosen according to the amount of data requested.
If certain tag responds with 200bits of information any other response
in the same time slot may corrupt the first reading.
By examination of two or more tags response, in a given time slot, one can predict there was a collision.
Decision about collision occurrence can be a spoiled Manchester code.
.
The Query-Tree (QT) [6] is also a way to cope with collision problems.
The QT algorithm consists of rounds of queries and responses.
In each round, the reader asks the tags whether any of their IDs contains a certain prefix.
If more than one tag answer (collision), then the reader knows that there are at least two tags having that prefix.
The reader then appends symbol '0' or '1' to the prefix, and continues to query for longer prefixes.
When a prefix matches a tag uniquely, and no collision is detected, tag can be identified.
Therefore, by extending the prefixes until only one tag's ID matches, the algorithm can discover all the tags.
.
다음의 그림 2.4.1.a은 프로토콜을 설명한다.



One conclusion can be drawn. Without help from tag side additional functions it is impossible to prevent collisions.
Only firmware side possibility of collision detection is possible to implement - any other method to fight
with collisions using simplest tags are unfeasible.
.
ATmega16을 사용한 RFID 읽기/쓰기 장치의 제작 #2 (하드웨어 설계)로 계속됩니다.
.
   
윗글 ATmega16 RFID #2 하드웨어
아래글 ISO 14443A RFID 카드의 읽기/쓰기 방법
    N         제목    글쓴이 작성일 조회 추천
AVR 자료실 안내 avrtools™ 2008/09/02 (화) 156 0
97 AVR Basic Compiler (4K Free) avrtools™ 2008/12/03 (수) 178 0
96 코드비젼 V2.05.0 평가판 avrtools™ 2011/07/17 (일) 119 0
95 8x8 LED Audio Spectrum Display avrtools™ 2009/10/18 (일) 241 0
94 AVR 펌웨어로 만드는 USB 드라이버 avrtools™ 2009/10/07 (수) 415 0
93 AVR-CDC and V-USB avrtools™ 2009/10/06 (화) 213 0
92 AVR USB-HID-Bootloader의 제작 avrtools™ 2009/10/01 (목) 249 0
91 AT91SAM7S256 개발환경과 컴파일러 [2] avrtools™ 2008/11/03 (월) 2165 0
90 SAM7S256 USB 드라이버와 AT91-ISP avrtools™ 2008/11/01 (토) 1148 0
89 AT91SAM7S256 공부를 시작합니다. avrtools™ 2008/11/01 (토) 575 1
88 ICCAVR V7.16A AVR 컴파일러 45일판 avrtools™ 2009/03/09 (월) 125 0
87 CodeVisionAVR1248b 最新版下载 leeky 2008/11/08 (토) 290 0
86 AVR UART 소스 (ICC AVR V6) avrtools™ 2008/12/03 (수) 165 0
85 cvAVR Soft Uart Source avrtools™ 2008/12/03 (수) 138 0
84 cvAVR 직렬포트와 LCD 시험용 소스 avrtools™ 2008/12/03 (수) 135 0
83 Free SmallC for AVR avrtools™ 2008/12/03 (수) 153 0
82 AVR910-ISP용 AVR-OSP2 Ver5.43 avrtools™ 2008/12/03 (수) 163 0
81 Code Vision AVR 컴파일러 2K 데모버전 avrtools™ 2008/12/02 (화) 92 0
80 AVR delay loop generator avrtools™ 2008/12/02 (화) 143 0
79 ICC tiny C컴파일러 V6 데모버전 (30일 제한판) avrtools™ 2008/12/02 (화) 61 0
78 ICC AVR C 컴파일러 V6 (4K 제한판) avrtools™ 2008/12/02 (화) 80 0
77 DasmAVR (Windows용 AVR 역어셈블러) avrtools™ 2008/12/02 (화) 126 0
76 AVR PROG KIT avrtools™ 2008/12/02 (화) 170 0
75 AVR JTAG ICE KIT avrtools™ 2008/12/02 (화) 240 0
74 AVR 부동소수점, 지연시간 계산기 avrtools™ 2008/12/02 (화) 142 0
73 ATtiny45 USB to RS232 인터페이스 avrtools™ 2008/09/26 (금) 188 0
72 MEGA32 128x64 GLCD Scope 제작 avrtools™ 2008/09/22 (월) 301 0
71 PC송신방식 Tiny2313 50x7 LED 전광판 avrtools™ 2008/09/10 (수) 253 0
70 mega8 적외선 거리측정 레이더 leeky 2006/05/07 (일) 1367 0
69 ATmega16 RFID #3 소프트웨어 leeky 2006/12/27 (수) 879 0
68 ATmega16 RFID #2 하드웨어 leeky 2006/12/27 (수) 1126 0
67 ATmega16 RFID #1 태그 leeky 2006/12/27 (수) 858 0
66 ISO 14443A RFID 카드의 읽기/쓰기 방법 [1] leeky 2007/02/25 (일) 1488 1
65 ATmega8 PSK31 RF Modem의 제작 leeky 2006/03/07 (화) 1376 21
64 T89C51SND1C 64M USB MP3 플레이어 avrtools 2006/03/04 (토) 968 8
63 AVR 13.56MHz RFID 읽기/쓰기 장치의 제작 [7] leeky 2007/02/19 (월) 994 4
62 WhereAVR for APRS GPS/Telemetry avrtools 2006/05/05 (금) 384 2
61 ATmega8 UI-TNC 무선모뎀의 제작 avrtools 2006/03/07 (화) 391 0
60 AVR APRS(GPS) Packet 무선모뎀 avrtools 2006/03/07 (화) 374 0
59 AT90PWM3 교류모터 속도제어 leeky 2006/04/07 (금) 921 1
58 M128 MMC LED 전광판 leeky 2006/03/07 (화) 911 0
57 Charon 2 이더넷 모듈의 소개 avrtools 2006/04/04 (화) 473 0
56 S2313 LED 회전계 (TACHO METER) avrtools 2006/03/28 (화) 597 0
55 Mega8 + 128x128 LCD 스코프 avrtools 2006/03/28 (화) 1185 0
54 Mega8 + OV6630 Treva 모바일용 카메라의 화상처리 leeky 2006/03/19 (일) 777 0
53 YUKI Mega8 MP3 Player #3 avrtools 2006/03/11 (토) 837 0
52 AVR JTAG 에뮬레이터의 제작 avrtools 2006/03/07 (화) 834 0
51 USB AVR 프로그래머 AvrUsb500 avrtools 2006/03/07 (화) 727 1
50 Mega88 USB 버스 모니터 avrtools 2006/03/07 (화) 384 0
49 M16 MMC Flash Memory leeky 2006/03/07 (화) 451 1
48 M163 SD,MMC Interface leeky 2006/03/07 (화) 435 0
47 S2313 MMC to Serial leeky 2006/03/07 (화) 315 0
46 ATmega48 UDP/IP 적외선 리모콘 수신장치 avrtools 2006/03/07 (화) 412 0
45 HDD MP3 플레이어 leeky 2006/03/07 (화) 596 0
44 MP3 yampp-3/USB leeky 2006/03/07 (화) 290 0
43 MP3 Player yampp-3 leeky 2006/03/07 (화) 254 0
42 YUKI MP3 플레이어2의 제작 (ATmega8 + SD Card) avrtools 2006/03/07 (화) 370 0
41 AVR CD 플레이어 leeky 2006/03/07 (화) 531 0
40 S2313 초음파 거리계 (미터, TV 스크린, LED 표시) avrtools 2006/03/07 (화) 544 0
39 RF Spectrum Monitor avrtools 2006/03/07 (화) 373 0
38 Easy Ethernet AVR 웹서버 leeky 2006/03/07 (화) 449 0
37 90S4433 LCD표시 100Mhz 주파수 카운터 leeky 2006/03/07 (화) 246 0
36 ELM Audio Spectrum Monitor avrtools 2006/03/07 (화) 352 0
35 Mega8 Door Bell leeky 2006/03/07 (화) 277 0
34 AVR 휴대용 DVM leeky 2006/03/07 (화) 482 0
33 Minimum Mass Waveform Capture and Display leeky 2006/03/07 (화) 260 0
32 AT90S2313 디지털 용량계 avrtools 2006/03/07 (화) 364 0
31 SLO2016 Alphanumeric Intelligent Display leeky 2006/03/07 (화) 174 0
30 AT90S2313 흔드는 LED 전광판 (POV) leeky 2006/03/07 (화) 426 0
29 ATtiny2313 Scrolling LED Sign avrtools 2006/03/07 (화) 363 0
28 Tiny22,S1200 나이트 라이더 avrtools 2006/03/07 (화) 308 0
27 ATtiny26L의 AD 변환과 PWM 출력제어 leeky 2006/03/07 (화) 474 0
26 S2313을 사용한 DS1820 온도계 leeky 2006/03/07 (화) 264 0
25 ATmega8535 온도센서 leeky 2006/03/07 (화) 294 0
24 AVR2313 100MHz RF연결 주파수 측정메터 avrtools 2006/03/07 (화) 193 0
23 VHF 무선 데이터 송신기 leeky 2006/03/07 (화) 502 0
22 90S2313 1MHz 파형 포착기 leeky 2006/03/07 (화) 227 0
21 VHF 무선 데이터 수신기 avrtools 2006/03/07 (화) 364 0
20 AVR 5x7 Dotmatrix LED leeky 2006/03/07 (화) 237 0
19 Mega163 웹 LCD leeky 2006/03/07 (화) 394 0
18 AVR 이더넷 시험소프트 avrtools 2006/03/07 (화) 296 0
17 AVR 넷트웍 시계 (타임 프로토콜) avrtools 2006/03/07 (화) 374 0
16 RS-232 to 100 MHz RF desktop avrtools 2006/03/07 (화) 235 0
15 AVR 6디지트 50MHz 주파수 카운터 leeky 2006/03/07 (화) 212 0
14 AVR DS1820 온도센서 avrtools 2006/03/07 (화) 251 0
13 AVR 직접주파수 발생기 (AT90S2313 DDS) avrtools 2006/03/07 (화) 371 0
12 프로그래머블 PLL 제어 avrtools 2006/03/07 (화) 219 0
11 AVR AT90S2313 7Segment LED Display leeky 2006/03/07 (화) 213 0
10 TINY15L 무전원 4채널 온도계 avrtools 2006/03/07 (화) 316 0
9 8PIN AVR을 사용한 풀컬러 LED leeky 2006/03/07 (화) 347 0
8 DS1820 고분해능 온도계 avrtools 2006/03/07 (화) 333 0
7 S2313 디지털 전압계 avrtools 2006/03/07 (화) 448 0
6 S2313 적외선 USB 모듈 avrtools 2006/03/07 (화) 317 0
5 S2313 주파수 카운터 avrtools 2006/03/07 (화) 253 0
4 AVR90S2313과 Treva 카메라의 연결 leeky 2006/03/07 (화) 294 0
3 Mega8 PID 온도제어 leeky 2006/02/24 (금) 530 1
2 90S2333 3채널 다이오드 온도계 avrtools 2006/02/24 (금) 236 0
1 AT89S8252로 만드는 1~40MHz DDS leeky 2006/02/14 (화) 309 0
1

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