Method and equipment for bidirectional data transmission (protocol)

Apparatus for half duplex bidirectional data communication with a direction of data signal transmission which is switchable and the transmission of data is in serial bit form with the time between successive data bit transmission being a period t.sub.a, said apparatus including first and second communicators (KP1, KP2), both comprising:

• a transmitter for transmitting data signals in response to transmission control signals;
• a receiver for receiving said data signals in response to receiver control signals, and
• a control unit connected to the transmitter and the receiver for generating said transmitter and receiver control signals and having a first memory element for identification as an initiating communicator (IKP) and a second memory element for identification as a receiving communicator (EKP);
• said control unit receiving a first input (Test) signal and a second input (Loop back) signal such that said first input (Test) is connected to said first memory element, and said second input (Loop back) is connected to said second memory element
• said control unit further including a means for generating transmit identification signals by which said first communicator identifies itself as a message initiating communicator (IKP) prior to transmitting a bit of a data signal;
• a means for generating receipt identification signals by which said second communicator identifies itself as a message receiving communicator (EKP) after receipt of a transmitted bit of a data signal;
• a means for broadcasting from said first communicator (IKP) a double length start bit (D) representing said first communicator identity at the beginning of each character of the data transmission;
• a means for waiting, by said first communicator, a defined time (t.sub.c) having about one half the duration of said time period t.sub.a ;
• a means for sending by said second communicator (EKP) back an echo signal in the form and duration of a single length start bit (B) during the defined time (t.sub.c) only after the reception of the double length start bit (D);
• a means for waiting, by the first communicator, for an echo signal after each transmitted data bit of a character;
• a means for comparing, by the first communicator, each transmitted data bit with the received echo bit;
• a means for breaking off transmission should a mismatch occur between said transmitted data bit and the received echo bit;
• and
• a means for generating signals to remove identification of said first and second communicators as initiating (IKP) and receiving (EKP) communicators.