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Keyboard Circuit

IP.com Disclosure Number: IPCOM000092425D
Original Publication Date: 1966-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Lankford, LG: AUTHOR

Abstract

The circuit generates the proper outputs when a second key of a keyboard is depressed before a first depressed key is released. The circuit is thus capable of handling the two-key roll situation.

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Keyboard Circuit

The circuit generates the proper outputs when a second key of a keyboard is depressed before a first depressed key is released. The circuit is thus capable of handling the two-key roll situation.

Ordinarily, when a key of keyboard 10 is depressed, coding circuit 12 generates the appropriate output on data lines 14 and also generates an output signal on any key line 16. Memory lockout flip-flop 18 is normally in its off state. Since no data is applied to the control circuit, not shown, there is no signal on restore line
19. Under these conditions, none of the inputs to Or 20 are present. Inverter 22 therefore generates an output signal on line 24. Such signal conditions gates 26 to pass the data on lines 14 through data output lines 28 to the external control circuit.

The signal on line 16 is applied as one input to And 30. When the data applied to the external control circuit is accepted by the circuit, a pulse is applied through line 19 to the other input of And 30. The latter is fully conditioned to generate an output signal on line 32 which is applied to set flip-flop 18 to its on state. The signal on line 19 is also applied to Or 20 causing an output signal which terminates the signal on line 24 thus blocking the flow of data to the external control device.

The setting of flip-flop 18 to its on state causes a signal to appear on line 34. Such signal maintains the output from Or 20 when the pulse on line 19 terminates, preventing any output fr...