enblock so to speak now the case is to be considered that such signaling characters are delivered from the memory unit se and that the polarity changes forming the signaling characters are retransmitted by way of the serving line laa the memory unit se emits such signaling characters from its direct command memory area dbz upon a corresponding control from the program control unit pe these signaling characters arrive at a character input of the conversion circuit seg c again assigned to the serving line laa by way of a line mtla and the communication control unit ueas and the system termination circuit sag c by way of the code converter acw these signaling characters are into a parallel series converter psu in the system termination circuit which then upon a corresponding control delivers individual polarity changes on its output side at a polarity change output to a line pwlb via the input code converter ecw the line plwb is connectible by way of the system termination circuit sag c and the communication control unit ueas with the memory cell zz2 of the memory unit se representing a serving cell in such a manner that the individual polarity changes are successively written into this memory cell which is assigned to the serving line laa the memory cell zz2 is assigned on its output side to the serving line laa of.