Abstract: The communications interface enables a processor unit to dialog with an IC card having an elementary time unit (ETU) for transmitting one bit that is equal to (K/Fs). The IC card includes a microprocessor, a clock pin for application of an external clock signal enabling the microprocessor of the IC card to be clocked, and an I/O pin. The microprocessor receives external data or transmits data via the I/O pin. The communications interface includes a serial communications line for interchanging data with the IC card via the I/O pin. The communications interface also includes a transmitting module, which is written-addressable by the processor unit and includes a serialization module for serializing and transmitting, over the serial communications line, data received from the processor unit. The communications interface also includes a receiving module, which is read-addressable by the processor unit and includes a serialization module for serializing data received over the serial communications line.