Abstract: An interface module for superimposing alphanumeric characters upon external GB video signals received by a SCART connector of a television set is disclosed. The interface includes a central processing unit (CPU) controlling the command input from an alphanumeric keyboard, remote control, touch screen functions, and message exchange with a processing center through the D channel of an ISDN network. The CPU controls a video display processor which outputs a switching signal to the SCART connector and R, G, B video signals to an encoder which encodes a composite color signal in a standard format such as PAL, SECAM or NTSC. The superimposing is done in the SCART connector by switching between the external R, G, B video signals and the composite color video from the encoder.

Abstract: A system for the exchange of messages among a multiplicity of processing units includes a data channel and a service line interconnecting respective interfaces of these units. Each interface includes a busy-state detector determining during a test phase of a recurrent time slot whether the service line is available, a logic network connectable in a subsequent acquisition phase the service line in the event of its availability to emit successive bits of an address characterizing the respective processing unit, and a comparator determining during the aquisition phase whether an emitted address bit of a particular logic level ("1") coincides with another bit of a higher-priority level ("0") concurrently sent over the line by some other unit. If a higher-priority address bit is encountered, the emission of the address is aborted and restarted in a subsequent time slot.