Abstract: A digital serial interface connects a transmitting device with a receiving device for communicating both data bits and synchronization signals via the serial interface. The transmitting device include a primary transmitter for converting a serial sequence of the data bits into successive data signal levels, and further includes a secondary transmitter for converting synchronization signals into synchronization signal levels different from the levels employed for the data signals. The receiving device has a primary receiver for the data signal levels for converting a sequence of data signal levels into a serial sequence of data bits, and further includes a secondary receiver fir the synchronization signal levels for converting synchronization signal levels into synchronization signals.

Abstract: For establishing a local communication connection between a terminal (102) of a cellular radio system and an accessory device (103), a radio channel is identified (301, 302) on which there is no perceivable radio traffic in the cellular radio system, and a communication connection is established (303, 501) between the terminal and the accessory device on the identified radio channel. The radio channel is preferably a code channel of a CDMA system.