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Browse Prior Art Database

Multiplexed Keyboard Control Signalling

IP.com Disclosure Number: IPCOM000043580D
Original Publication Date: 1984-Sep-01
Included in the Prior Art Database: 2005-Feb-05
Document File: 2 page(s) / 35K

Publishing Venue

IBM

Related People

Curtis, CS: AUTHOR [+3]

Abstract

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.

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Multiplexed Keyboard Control Signalling

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. However, if the incoming signal on line 1 does not persist for the full two milliseconds, AND gate 3 will not be activated. This can provide at output 4 a normal logic function signal for whatever purpose the input is ordinarily provided. For example, the signal on line 1 may be an indication to the keyboard to emit a tone as an indication that the input has been received by the terminal directly, or a control signal to supply a different mode of operation or the like. The incoming signal is also supplied to pulse generator 5 and through an inverting input to AND gate 7. Circuit 5 supplies a pulse to AND gate 7 when the incoming signal becomes active. If the signal is removed before the pulse becomes inactive, output 8 will be active for the duration of the pulse. However, if the incoming signal is activ...