The Architecture of Electronic Data Carriers - RFID: Fundamentals and Applications in Contactless Smart Cards and Identification - page 273

Analog front end 95 10155

Modulator
FSK
PSK
BIPH
Manchester

Mod

Data

Load

R R6
R5
R R3
R R1
R0

Coil

128 bit PROM

Clk

Clock
extractor

Coil Column decoder

Rectifier

Bitrate

Counter

VDD VSS

Figure 10.10 Block diagram of a read-only transponder. When the transponder enters the
interrogation zone of a reader a counter begins to interrogate all addresses of the internal
memory (PROM) sequentially. The data output of the memory is connected to a load modulator
which is set to the baseband code of the binary code (modulator). In this manner the entire
content of the memory (128-bit serial number) can be emitted cyclically as a serial data stream
(reproduced by permission of TEMIC Semiconductor GmbH, Heilbronn)

therefore animal identification, access control and industrial automation with central
data management.
A low-cost transponder chip is shown in Figure 10.11.

10.1.3.2 Writable transponder

Transponders that can be written with data by the reader are available with mem-
ory sizes ranging from just 1 byte ('pigeon transponder') to 64 Kbytes (microwave
transponders with SRAM).
Write and read access to the transponder is often in blocks. Where this is the case,
a block is formed by assembling a predefined number of bytes, which can then be read
or written as a single unit. To change the data content of an individual block, the entire
block must first be read from the transponder, after which the same block, including
the modified bytes, can be written back to the transponder.
Current systems use block sizes of 16 bits, 4 bytes or 16 bytes. The block structure
of the memory facilitates simple addressing in the chip and by the reader.

10.1.3.3 Transponderwith cryptological function

If a writable transponder is not protected in some way, any reader that is part of the
same RFID system can read from it, or write to it. This is not always desirable, because