Abstract: A microcomputer integrates a Digital Subscriber Terminal (DST) adapted to an Integrated Services Digital Network (ISDN). In addition to the electronic circuit boards that ensure all the normal data processing and management functions (central processing unit, input/output circuits, ROM and RAM circuits), the microcomputer is equipped with an additional set of circuit boards for interfacing with an ISDN system, so as to constitute a microcomputer-contained DST for an ISDN. The management and switching of data concerning the ISDN system are provided by the additional set of circuits, so that the DST function is achieved without calling on the resources of the microcomputer's central processing unit. In this way, the essential telephone switching function is obtained without calling on the PC's central processing unit, while the integration of the DST within the PC makes it possible to benefit from the computer's data processing functions with a minimum amount of equipment for a maximum number of functions.

Abstract: An analog amplifier multiplexer for a data system in which a plurality of differential signal channels are multiplexed onto a pair of differential signal lines includes a differential amplifier connected to each pair of differential signal lines which are to be multiplexed and a current switch connected to each differential amplifier which ensures that an individual differential amplifier will amplify the differential signal applied to it only when it is selected to do so by a selection signal. The selection signal and the current switch ensure that only one differential amplifier amplifies its corresponding differential signal and supplies it to an additional circuitry at any one time.

Abstract: A multiplexer module includes N input transistors (T.sub.0 to T.sub.3) whose bases receive input signals (E.sub.0 . . . E.sub.3), whose collectors are connected to ground and whose emitters are coupled to those of a multi-emitter output transister T'.sub.4. A logic addressing circuit (ALC) connects a current source I to one of the emitters of the input transistors (T.sub.0 to T.sub.3) as a function of an address (A.sub.0, A.sub.1) received. Any reference voltage on the output transistor (T'.sub.4) is suppressed by short-circuiting its base and its collector which constitutes the output S' which is connected to ground by way of an output resistor R'.sub.s. The module may be connected to other modules (having e.g. K inputs) within the same circuit, notably in order to realize a multiplexer having N.sup.k inputs without giving rise to stray coupling between the outputs of the various modules.