User manual

SCM3712 REFERENCE MANUAL 16
3.4.1. 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.
3.4.2. 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 used 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 of this document 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.