Multiplexed Keyboard Control Signalling
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-05
Keyboards may be controlled or configured for different data from commands issued from an attached terminal. However, there is a need to reduce the number of new wires at the interface, and in some designs, pin limitations prevent the addition of new leads. The present disclosure shows a method of multiplexing a signal on a single lead by the time duration measurement of a signal level presented to the keyboard. In the figure, the signal comes on lead 1 from an attached terminal (not shown). A delay circuit 2 will present an output to an AND gate 3 when, for example, a two-millisecond delay has elapsed. The other input to AND gate 3 is the signal on line 1 itself so that AND gate 3 will be activated only after the two-millisecond delay has elapsed.