TA259 Technical article
Designing low-cost large-volume close-coupling contactless systems with ST contactless memories and coupler
The ability to identify, track, and update the information on objects: this is a facility that is now in ever increasing demand. Radio frequency (RF) identification technology was developed as an alternative to existing systems, such as the magnetic stripes and contact memory ICs. A contactless system is composed of several components: a reader and a set of contactless memory tags. Each tag consists of a small memory chip, connected to a small coil antenna. The memory chip holds identification and data for the item to which it is attached. The antenna acts as one winding of a transformer for passing RF power into the memory chip, and passing modulated data in and out. Contactless identification applications are considered to work in the close coupling range when the distance between items to reader is lower than 2 cm. Among the applications that are expected to form the basis for rapid growing of close coupling identification are:
Identification and tracking of consumable Prepaid cards for vending machines Industrial identification
They are all large volume applications. To be successful in this market, and to compete with existing solutions, contactless identification systems must meet a number of requirements:
Reader and tags must be compliant with ISO proximity standards (such as ISO14443 type B) Low cost embedded reader Operating in the close coupling range Memory capacity might need to be high to hold all the necessary tracking information Security features (such as anti-cloning or password protection)
ST has specifically designed the CRX14 contactless coupler, and a family of short range contactless memory devices to be used together when designing low cost contactless systems, optimized for close coupling operation.
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The CRX14 contactless coupler chip
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The CRX14 contactless coupler chip
ST has designed the CRX14, a short range contactless coupler chip compliant with ISO14443 type B proximity standard. The CRX14 generates a 13.56 MHz frequency signal. Designed to deliver an RF power of 100 mW, it operates in the close coupling range when associated with ISO14443 type B contactless memory tags. It is equipped with the ST anti-collision mechanism, which allows the reader to detect and identify all tags present in the operating range and to access them individually. Because the CRX14 implements the France Telecom-proprietary anti-clone function, the reader can perform authentication of tags that are also equipped with the France Telecom anti-clone capability. The CRX14 coupler interfaces with the memory tags, on one side, through input/output buffers and the ISO14443 type B radio frequency protocol, and to the system master processor, on the other side, through a 400 kHz I2C bus. Operating from a 5 V power supply, and delivered in a SO16N package, the CRX14 coupler chip is an excellent solution for building contactless readers, embedded in the final equipment, and offering a good compromise between operating range and cost.
Short range contactless memories
All devices from the ST short range contactless series are compliant with the ISO14443 type B standard. They are accessible via a 13.5 MHz carrier frequency, and support a data transfer rate between tag and reader of 106 kbit/s in both reception and emission modes. All devices are totally compatible with each other, in terms of tag protocol access. The series is sub-divided into two families: Standard SRxxxx family
Secure SRIXxx family (equipped with anti-clone and anti-collision capabilities)
Standard SRxxxx family
SRI512 is the first member of ST standard short range family. It is deprived of anti-clone functions and offers 512 bits of EEPROM organized as 16 words of 32-bits. These are, in turn, organized in three main areas:
A 5-word OTP zone, accessible in user mode, whose bits can only be switched from 1 to 0 Two 32-bit binary counters which can only be decremented 9 words of user EEPROM which can be individually write protected
The second member is the SRT512 dedicated to transport ticketing applications. It features 512 bits of EEPROM organized as 16 words of 32-bits, except that the memory is organized into two areas:
Two 32-bit binary counters which can only be decremented 14 words of user EEPROM which can be individually write protected
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TA259Designing close coupling systems with CRX14 coupler and short range contactless memoBoth products offer an 8-bit chip identifier allowing a reader to identify uniquely each tag present in its field during anti-collision operations and a 64-bit read-only unique identifier (UID) programmed on the manufacturing line.
Secure SRIXxx family
SRIXxx is a family of highly secure devices that support the anti-clone capability, allowing tag authentication. The system master processor sends an authentication request, in turn, to each of the tags present in the CRX14 field. Each tag runs its anti-clone algorithm to compute a signature, that is sent back to the reader for an authentication check. The anticlone function helps fight against fraud, since any tag that does not belong to the system will answer with a wrong signature. The spearhead of the SRIXxx family is the SRIX4K, featuring 4096 bits of EEPROM organized as 128 words of 32 bits. These are, in turn, organized in three main areas:
A 5-word OTP zone, accessible in user mode, whose bits can only be switched from 1 to 0 Two 32-bit binary counters which can only be decremented 121 words of user EEPROM, of which 9 can be individually write protected
The SRIX4K offers an 8-bit chip identifier allowing a reader to identify uniquely each tag present in its field during the anti-collision operation and a 64-bit read-only unique identifier (UID) programmed on the manufacturing line.
Designing close coupling systems with CRX14 coupler and short range contactless memories
SRIXxx and SRxxxx contactless memory chips are packaged with an antenna, embedded in one of a variety of formats (inlays, token, button). The whole assembly is attached to the item that is to be identified and tracked. For the embedded reader, the ST CRX14 coupler chip must be connected to an antenna, to transmit and receive the RF signal from and to the tags, and to an industrial standard I2C serial bus, to interface with the system master processor (see figure 1). The power transfer from reader to the tag and the RF communication are performed through an inductive coupling between the two coils at the frequency of 13.56 MHz. The tag does not need a dedicated power supply (such as a battery). The reader is equipped with a tag-dedicated software driver supporting tag read and write operations. A CRX14-based reader interoperates with any short range contactless memory from ST or ISO14443 type B compatible devices from other manufacturers. For contactless identification applications, working in the close coupling range and requiring a high level of security, such as consumable identification and anti-counterfeiting, it can be used with secure SRIX-based tags equipped with the anti-clone authentication function. If, though, authentication is not needed, but cost reduction is the key requirement, a CRX14-based reader paired with standard SRI512 or SRT512 contactless memories is the ideal solution. Example applications include low-value pre-paid tokens that do not need to be modified more than a few times.
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Designing close coupling systems with CRX14 coupler and short range contactless memories Figure 1. Vending machine with contactless payment interface
Low-pass Filter RF Out I2C Bus System Master Processor CRX14 Coupler Band-pass Filter RF In Short Range Contactless Memory (SRIX4K, SRI/SRT512, ISO14443-B)
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LCD Display Module
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Close coupling applications
Identification and tracking of consumable (food, batteries, computer peripherals such as printer cartridges, storage cartridges) are among the main potential applications of close coupling identification. These high volume applications require low cost readers, sometimes embedded in the equipment itself, operating with a single or a limited number of tags. For these applications, a CRX14-based reader, paired with SRIX4K tags, is the best solution. The 64-bit UID can be used to identify the item, while the lockable zone can contain manufacturing data such as the serial number. The 112 extra non-lockable words can be used to store system history information. The anti-clone capability, offered by the SRIX4K, allows counterfeit-detection through item authentication, while the anti-collision function performs multi-tag recognition. Prepaid cards for vending machine are another good example of application that can greatly benefit from using close coupling contactless identification systems. SRIX4K contactless memories are embedded into each token. One of the two 32-bit binary counters is uploaded with an initial purchase value and decremented at each transaction. The token identifier is stored in the 64-bit UID block and manufacturing data such as serial number or point-of-sale information in the lockable zone. They are much more robust than magnetic cards and contact cards. Targeted applications of the lower cost short range family, without high security, are identification and tracking of manufactured goods on the production line, where process control data are stored in user EEPROM.
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Conclusion
Conclusion
With the use of the single chip coupler CRX14 associated with ST SRIXxxx or SRxxxx short range contactless memories, low cost contactless identification systems, with a high level of security (authentication, anti-cloning) and operating in the close coupling range, can be built with ease. Compared with existing identification systems, the close coupling solution has outstanding advantages: they are robust since they can operate in harsh conditions, available at low cost and flexible. The contactless memory system provides an automatic, quick and easy way to collect information about one or multiple items in a production flow, independently from position, and without the need of direct optical link or of human intervention. In addition, contactless identification frees the user from harsh or dirty environment concerns that restrict other automatic identification solutions. It can be used as a bidirectional data carrier since it allows information attached to the item to be written and to be updated on the fly.
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Revision history
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Revision history
Table 1.
Date 20-Nov-2007 07-Nov-2008
Document revision history
Revision 1 2 Initial release. Replaced SR176 by SRI512 and SRT512. Renamed low-end SR by standard SR devices. Changes
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