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Browse Prior Art Database

Keyboard with Integral Pin Pad Attachment

IP.com Disclosure Number: IPCOM000089531D
Original Publication Date: 1977-Nov-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 90K

Publishing Venue

IBM

Related People

Harring, CA: AUTHOR

Abstract

Circuitry for unambiguously receiving key strokes from a main keyboard 10 and a cable 12 attached personal identification number (PIN) input keypad 11 is shown. Each keyboard comprises a matrix of eight horizontal scan lines and a plurality of vertical output columns, the number of output columns being dependent on the number of keys in the keyboard. For example, main keyboard 10 has 8 output columns 0-7 and FIN keypad 11 has only 2 output columns A and B.

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Keyboard with Integral Pin Pad Attachment

Circuitry for unambiguously receiving key strokes from a main keyboard 10 and a cable 12 attached personal identification number (PIN) input keypad 11 is shown. Each keyboard comprises a matrix of eight horizontal scan lines and a plurality of vertical output columns, the number of output columns being dependent on the number of keys in the keyboard. For example, main keyboard 10 has 8 output columns 0-7 and FIN keypad 11 has only 2 output columns A and B.

In order to unambiguously detect a key depression which provides a connection at the intersection of a scan line and output column, keyboard scan counter 13 sequentially energizes horizontal scan lines 0-7 with negative voltage pulses. Thus, only one horizontal scan line is being interrogated at any one time. Likewise, keyboard sample counter 15 sequentially activates gates 17 with nonoverlapping negative sample pulses 0-7, A, B so that even though two keys may be simultaneously depressed, connecting one scan line to more than one output line, only one of the depressed keys will be detected at a time and an unambiguous output will be received.

The output columns 0-7, A, B are provided to negative AND gate 19, each having ten input terminals. A negative AND gate provides a positive voltage output signal when all inputs are receiving negative voltage signals. Each AND gate 19 receives one keyboard output column and 9 feedback lines from keyboard output column latches 23. For example, the AND gate 19, corresponding to keyboard output column 6, has an input from keyboard flip latches 0-5, 7, A, and B. Thus, only if none of these latches is set will keyboard flip latch 6 be set through corresponding inverter 21 and negative AND gate 17.

The output of corresponding negative AND gate 17 is connected to OR gate 25, which increments four-bit delay counter 27. Having been incremented, four- bit delay counter 27 provides a positive signal to OR gate 29, which provides a negative output signal to be inverted by inverter 31 and inhibit AND gate 33, thereby inhibiting further stepping of keyboard scan counter 13. Keyboard sample counter 15, however, cont...