Keyboard scanning appts. for detecting key depressions - identifies key from return line and from temporal location of pulse on line, using shift register and processor

摘要

The appts. detects key depressions on a keyboard with a number of keys, which make contact when activated between one of several feed lines (Z1...) and one of several return lines (RL1...) of a matrix of lines. The return lines are coupled to a control unit (ST) which applies a test signal to each of the feed lines in succession and, in accordance with the appearance of the signal on one of the return lines, identifies the key pressed and the time of this event. The keyboard has a section with a clock input (CLK), a data input (D) and a number of shift register places (Q1...) corresponding to the number of feed lines, along with another shift register, with an input for receiving the sampling signals timed by a clock in succession. ADVANTAGE - Number of keys scanned may be increased without substantial circuit alteration.