Computer interface system

An interface logic circuit, comprising:

• a serially connected bidirectional shift register having input terminals at either end for entering logic level signals of opposite polarity, a clocking terminal and a mode control terminal for determining the direction of shift of said bidirectional shift register;
• means for entering fixed logic level signals of opposite polarities at opposite ends of said bidirectional shift register in response to the character of a request to transmit signal received from a remote location;
• means operably connected to one of the storage locations of said bidirectional shift register for generating a response signal responsive to a predetermined state of said one register;
• a unidirectional shift register having at least one clocking terminal, a signal input terminal, a plurality of output terminals corresponding to the individual storage locations within said unidirectional shift register, and parallel feed input terminals associated one each with the individual storage locations within said unidirectional shift register;
• means for applying a logic level signal of a predetermined polarity to a preselected one of the storage locations in said unidirectional shift register in response to a ready signal received from said remote location;
• and
• means for overriding the state of a preselected one of the storage locations in said unidirectional shift register with a logic level signal of a polarity opposite to said predetermined polarity, in the absence of an input signal to said unidirectional shift register.