Serial keyboard interface system.

摘要

A keyboard interface for a data processing system in which a keyboard (6) and a data processing unit (8) are connected through a single clock line (4) for transmitting a keyboard out clock signal and a single data line (2) for transmitting a serial bit frame having a serial scan code identifying a depressed key in synchronism with the clock signal is disclosed. The interface uses a transmission error detection and resend procedure to prevent transmission error due to noise pulse induced on the clock line (4) as by electrostatic discharge to give rise to extra data sampling. The unit returns a status signal acknowledging the receipt of a frame to the keyboard (6) through the data line (2) immediately after the number of sampled bits received by the unit reaches the predetermined number of bits of a frame. The keyboard checks whether the status signal has been returned after the completion of transmission of a frame and, if not, returns a negative response to the unit through the clock line, then resending the same scan code. The interface permits the use of a low cost, low noise-tolerance stretch cable without shield.