Information Processing in the Transponder
If we classify RFID systems according to the range of information and data processing functions offered by the transponder and the size of its data memory, we obtain a broad spectrum of variants. The extreme ends of this spectrum are represented by low-end and high-end systems.

EAS systems (electronic article surveillance systems) represent the bottom end of low-end systems. These systems check and monitor the possible presence of a transponder in the interrogation zone of a detection unit’s reader using simple physical effects.
Read-only transponders with a microchip are also classified as low-end systems. These transponders have a permanently encoded data set that generally consists only of a unique serial number (unique number) made up of several bytes. If a read-only transponder is placed in the RF field of a reader, the transponder begins to continuously broadcast its own serial number. It is not possible for the reader to address a read-only transponder – there is a unidirectional flow of data from the transponder to the reader. In practical operation of a read-only system, it is also necessary to ensure that there is only ever one transponder in the reader’s interrogation zone, otherwise the two or more transponders simultaneously transmitting would lead to a data collision. The reader would no longer be able to detect the transponder. Despite this limitation, read-only transponders are excellently suited for many applications in which it is sufficient for one unique number to be read. Because of the simple function of a read-only transponder, the chip area can be minimised, thus achieving low power consumption, and a low manufacturing cost.
Read-only systems are operated at all frequencies available to RFID systems. The achievable ranges are generally very high thanks to the low power consumption of the microchip. Readonly systems are used where only a small amount of data is required or where they can replace the functionality of barcode systems, for example in the control of product flows, in the identification of pallets, containers and gas bottles (ISO 18000), but also in the identification of animals (ISO 11785).
The mid-range is occupied by a variety of systems with writable data memory, which means that this sector has by far the greatest diversity of types. Memory sizes range from a few bytes to over 100 Kbyte EEPROM (passive transponder) or SRAM (active, i.e. transponder with battery backup). These transponders are able to process simple reader commands for the selective reading and writing of the data memory in a permanently encoded state machine. In general, the transponders also support anticollision procedures, so that several transponders located in the reader’s interrogation zone at the same time do not interfere with one another and can be selectively addressed by the reader.
Cryptological procedures, i.e. authentication between transponder and reader, and data stream encryption are also common in these systems. These systems are operated at all frequencies available to RFID systems. The high-end segment is made up of systems with a microprocessor and a smart card operating system (smart card OS). The use of microprocessors facilitates the realisation of significantly more complex encryption and authentication algorithms than would be possible using the hard-wired logic of a state machine. The top end of high-end systems is occupied by modern dual interface smart cards, which have a cryptographic coprocessor. The enormous reduction in computing times that results from the use of a coprocessor means that contactless smart cards can even be used in applications that impose high requirements on the secure encryption of the data transmission, such as electronic purse or ticketing systems for public transport. High-end systems are almost exclusively operated at the 13.56 MHz frequency. Data transmission between transponder and reader is described in the standard ISO 14443.