SCL3711
R
EFERENCE
M
ANUAL
14
3.5.
Contactless communication principles and SCL3711
usage recommendations
SCL3711 is a contactless reader
1
designed
to communicate with user tokens.
User tokens
2
are made of a contactless
integrated circuit card connected to an
antenna
User tokens can take several form factors:
•
Credit card sized smart card
•
Key fob
•
NFC mobile phone etc…
Communication between SCL3711 and user tokens uses magnetic field inductive coupling.
The magnetic field generated by SCL3711 has a carrier frequency of 13.56MHz.
3.5.1. Power supply
When the user token is put in the magnetic field of the reader, its antenna couples with the
reader and an induction current appears in the antenna thus providing power to the integrated
circuit. The generated current is proportional to the magnetic flux going through the antenna of
the user token.
3.5.2. Data exchange
The carrier frequency of the magnetic field is used as a fundamental clock signal for the
communication between the reader and the card. It is also use as a fundamental clock input for
the integrated circuit microprocessor to function.
To send data to the user token the reader modulates the amplitude of the field. There are
several amplitude modulation and data encoding rules defined in ISO/IEC 14443 and ISO/IEC
18092. The reader should refer to those standards for further details.
To answer to the reader, the integrated circuit card of the user token modulates its way of
loading (impedance) the field generated by the reader. Here also further details can be found in
ISO/IEC 14443 and ISO/IEC 18092.
1
In the ISO/IEC 14443 standard, the reader is called the proximity coupling device (PCD)
2
In the ISO/IEC 14443 standard, the user token is called proximity integrated chip card (PICC)
User tokens
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