Title:
PUSHBUTTON KEYBOARD SWITCH ARRAY AND ASSOCIATED PRINTED CIRCUIT LOGIC CARDS
United States Patent 3676615


Abstract:
In a keyboard, an elastic diaphragm switch array and logic, including strobe and rollover protection. The switch includes a diaphragm, a separator, and a switch card. The diaphragm comprises a gold plated continuous sheet of thin spring material and serves as a ground or voltage plane. The switch card has a gold plated pie pattern or switch array at each key location, with generally as many pie sections as there are bits in the code to be produced. Each pie section is wired directly by double sided wiring and through-holes in the switch card to the appropriate output code pin. No decoding or encoding logic is required to produce the code. Strobe logic is provided for assuring that all pie sections have made contact with the diaphragm and rollover protection logic is provided for assuring that only one key is depressed. A key button is provided for pressing the diaphragm through the separator to make contact with the switch card pie pattern.



Inventors:
WIEDMER FRITZ S
Application Number:
05/054300
Publication Date:
07/11/1972
Filing Date:
07/13/1970
Assignee:
INTERN. BUSINESS MACHINES CORP.
Primary Class:
Other Classes:
200/5R, 200/517, 341/34
International Classes:
H01H13/702; H03M11/22; (IPC1-7): H01H9/26; H01H13/52
Field of Search:
200/1R,5R,5E,16A,83R,86R,159B 317
View Patent Images:
US Patent References:



Primary Examiner:
Scott J. R.
Claims:
What is claimed is

1. A keyboard apparatus, comprising:

2. The keyboard means of claim 1 further comprising rollover protection logic means responsive to the output code at said pins for detecting simultaneous electrical contact between said diaphragm and a plurality of switching elements of different arrays.

3. The keyboard of claim 1 further comprising strobe logic means responsive to the output code at said pins for detecting electrical contact between said diaphragm and all of the switching elements of an array.

4. In an elastic diaphragm keyboard apparatus, a switch actuator means for moving the elastic diaphragm means into contact with a selected array of switching elements, comprising:

5. The keyboard apparatus of claim 4 further comprising distributor means disposed between said switch actuator means and said diaphragm means for transmitting the actuation force from said switch actuator means to said diaphragm means.

6. A keyboard comprising:

7. The keyboard of claim 6 wherein said output locations comprise a plurality of groups of output connectors, one of said groups being uniquely associated with a corresponding switching element from each said array, each said switching element being connected by double sided wiring to one and only one output connector of its associated group.

8. The keyboard of claim 7 further comprising rollover logic means for detecting the presence of positive logic levels at more than one output connector of any of said groups of output connectors.

9. The keyboard of claim 7, further comprising strobe logic means responsive to the output code at said output connector means for detecting that each group of output connectors has a positive logic signal on one of its output connectors.

10. An electronic keyboard apparatus having a plurality of key locations for generating a unique output code for each key, comprising:

11. The keyboard of claim 2 further comprising strobe logic means responsive to the output code at said pins for detecting electrical contact between said diaphragm and all of the switching elements of an array.

12. The keyboard of claim 8, further comprising strobe logic means responsive to the output code at said output connector means for detecting that each group of output connectors has a positive logic signal on one of its output connectors.

Description:
BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to electrical switching elements for generating an output code, and more particularly to an array of pressure-sensitive elastic diaphragm switching elements which are double sided wired on a switch card to output pins and thence to strobe and rollover protection logic.

2. Description of the Prior Art

U.S. Pat. No. 3,308,253 by M. Krakinowski, and of common assignee, describes a diaphragm switch having a diaphragm supported on an incompressible layer and an elastomer overlaying the diaphragm. When pressure is applied to the elastomeric material, the elastomeric material and the diaphragm are deformed to bring the terminals into contact with each other. In Krakinowski, at least two embodiments are shown: the first being one in which strips of conducting materials are oriented perpendicular to each other and the switching points oriented in the matrix array, and a second embodiment where the array is constructed by coating the entire underside of the diaphragm 18 with conducting material or using a diaphragm of conducting material and providing an individual conducting segment for each index position. In the latter embodiment, a single lead is connected to the conducting layer under the diaphragm and an individual output lead is provided for each of the segments. Thus, in Krakinowski, each key or index position must be determined by decoding the XY coordinates or the single lead. It then becomes necessary, in the event that an output code is desired, to provide logic for decoding the index point for the given XY coordinate.

Another prior art keyboard provides a binary encoding device including a key which selectively interconnects multiple electrical conductors or circuits which are printed or otherwise arranged in parallel on a flat base member. Each key includes plurality of metallic circuit closing or shunting bars having variously spaced projecting contact members thereon which, when actuated selectively draw current through one or more of the parallel electrical conductors. One severe limitation on the usefulness of this prior art device is the number of different output pins which may be utilized; that is, a conductive line for each output pin must pass beneath each key position. And yet, they must not be spaced so closely that the shunting bars cannot make distinct contact with individual conductive lines.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an improved pressure responsive electrical switching element.

A more specific object of this invention is to provide an improved diaphragm, pressure-responsive switching element.

It is a further object of the invention to provide an improved pressure-responsive diaphragm switch having a plurality of switching elements or pie sections which are double wired to output pins for producing an output code directly without decoding or encoding logic.

It is a further object of the invention to provide an improved elastic diaphragm switch keyboard with strobe logic for assuring that all pie sections have made contact with the diaphragm.

It is a further object of the invention to provide an improved elastic diaphragm keyboard having rollover protection logic for assuring that only one key is depressed when transmitting the output code.

The above objects are achieved by the invention which provides an electronic switch means comprising at least one key button, an elastic diaphragm means, separator means, and a switch card means. The switch card comprises a substrate and at least one array of switching elements or pie sections. A plurality of the switching elements or pie sections are electrically connected by double sided wiring on the substrate to the output pins. The elastic diaphragm comprises a thin continuous sheet of conductive and spring material which may be deflected by the key button through the separator into electrical contact with the array of switching elements or pie sections. Double sided wiring connects the pie sections to the output pin for generation directly of the output code from the switching array. Detection of simultaneous electrical contract between said diaphragm and a plurality of switching elements of different arrays is provided by rollover protection logic. Similarly, detection of electrical contact between said diaphragm and all of the switching elements of an array is provided by strobe logic means.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-section view of the key button, the elastic diaphragm, the separator and the switch card for use in the keyboard of the invention.

FIG. 2A shows the pattern of pie sections and conductors on the top side of a switch card; and

FIG. 2B shows the pattern of conductors on the bottom side. The dark dots shown on the conductive land patterns represent thru holes for connecting the top and bottom conductors.

FIG. 2C is a logic diaphragm of the circuitry required for rollover protection and strobing of the code generated at the output pins of FIGS. 2A and 2B.

FIG. 3 shows the switch card array for a ten key keyboard utilizing a 3 out of 14 code and the associated logic for strobe and rollover protection.

FIG. 4A shows the switch card array for a 10 key keyboard and associated rollover protection and strobe logic for generating an EBCDIC code.

FIG. 4C describes in greater detail the Data Selector/Multiplexer (DS/M) of FIG. 4A.

FIG. 5 is a perspective view of a console and its internal parts illustrating the structural layout of a keyboard.

ELASTIC DIAPHRAGM SWITCH KEY CONSTRUCTION

Referring now to FIGS. 1 and 5, a description will be given of the elastic diaphragm switch key including the button 40, diaphragm 51, and switch card or base 60.

FIG. 5 illustrates a plurality of buttons 40 in a keyboard console array and their relationship, in perspective view, to the various layers 50-54, and 60 shown in sectional view in FIG. 1.

Key button (or actuator means) 40 is a round button shown in cross-section through the center line in FIG. 1. Finger area 41 of the button is shown concave but may also be convex, flat, sunk into the face plate 30, flush with or raised above the face plate 30. Face plate 30, layers 50-54 and 60, logic card 55, are mounted as by screws (not shown) in base 56. The outside diameter or gliding surface 42 of button 40 rides within the hole 31 in face plate 30. Hole 31 further includes a cone area 32, a ledge area 33, and a larger diameter surface 34. Cone area 32 serves to reduce the area of contact between the hole 31 and the button 40, ledge 33 prevents the button 40 from moving upwards out of hole 31.

Button 40 further includes an annular ball portion 44 having a well portion 43 for catching dirt, etc., that may fall between hole 31 and button surface 42. Annular ball section 44 is in the form of a spherical ball when viewed as shown in FIG. 1 for allowing the button 40 to rotate only around the center of the ball 44 and thus prevent binding of the button 40 between surface 42 and hole surface 31. The bottom surface of annular ball 44 comprises a button actuator stop surface 45 for preventing damage to the elastic diaphragm 51 and for giving the desirable force/displacement curve for the actuator 46.

Actuator 46 extends a distance W beneath the surface of annular stop 45, and in cooperation therewith gives a reliable or repeatable actuation of the elastic diaphragm independent of the finger force characteristics of the keyboard operator.

Distributor layer 50 has several functions. It protects the elastic diaphragm from hard actuation by actuator 46 directly, and from any rough spots on said actuator. The fact that the travel of actuator 46 into the separator 50 is limited by the stop surface 45 further protects the elastic diaphragm layer 51 from accidental or malicious blows on the button 40.

The actuator 46 plays a material role in the determination of the force/displacement characteristics. Its length W determines the button stoke and its diameter together with the hardness and thickness of the separator layer 50 determines the button force. Thus, a soft and thick distributor 50 gives a light, long button stroke, and vice versa. In general, the softness and thickness of distributor 50 and the dimension W have to be increased and decreased together. But the precise relative selection allows a light button to have a long stroke, or allows a button of any stroke to be made with a lighter or harder touch. Of course, the shape of actuator 46 (that is, whether it is round or flat on the bottom) also plays a role in the force/displacement characteristics of the button, as do the physical characteristics of the elastic diaphragm area 51 and the separator layer 52. Finally, another function of the distributor 50 is to produce a force on the diaphragm 51 that spreads from the center (i.e., the center line of button 40) to the edge and does so over a finite length of the button travel while at the same time increasing the force from the center to the edge.

The feature of a key button 40 of the design shown with a actuator 46 and a distributing ring 45 together with a relatively thick, soft distributor 50 permits repeated, reliable operation of the key. The key further includes a separator layer 52 having an opening V through which the elastic diaphragm 51 is pressed into contact with the array of pie sections (that is, switching elements) on the top surface of switch card 60. The bottom and top surfaces of switch card 60 have conductive land patterns deposited or otherwise provided thereon and via holes as necessary to interconnect the top and bottom land patterns, as will be described in connection with the preferred embodiments of keyboards to be described hereinafter.

Isolator section 53 isolates the switch card 60 from the back plate 54. Logic card 55 is shown herein, positioned between plate 54 and base 55. The various layers 50, 51, 52, 60, 53, and 54 may be merely placed upon each other and held together by screws or other mechanical fasteners as will be obvious to those skilled in the art.

Diaphragm 51 comprises, for example, 1/2 to 1 mil Berylco 25 (a beryllium copper spring alloy) plated with 150 micro inches of gold. Varying the thickness of the Berylco 25 in the copper varies the actuating force of the switch very little. The actuating force is determined by the distributor-actuator combination and the separator thickness.

Separator 52 comprises two to three mils of Mylar, with three mils preferred because it tends to make the switch less sensitive to imperfections in the bottom surface of diaphragm 51. Together with a quarter inch hole in the separator 52, the three mils thickness Mylar separator 52 makes a sensitive switch that keeps stresses in the diaphragm 51 low.

Herein, switch card 60 comprises a base of copper clad epoxy board. Isolator 53 comprises, for example, 3 mils Mylar, which is not necessary of course if back plate 54 is non-conductive. Said back plate 54 is optionally provided to re-enforce the switch card 60 against abuse.

Referring now to FIGS. 2A and 2B, one preferred embodiment of the invention for an elastic diaphragm switch key board array will be described. FIG. 2A represents a land pattern on the "Y" side of a switch card (refer to FIG. 1) which will be contacted by the elastic diaphragm. FIG. 2B represents a pattern of conductors on the "Z" side of the switch card (refer to FIG. 1), opposite from the elastic diaphragm. FIGS. 2A and 2B are viewed from the same position, such that the output pins 61 through 68 appear in the same orientation in both figures. Each key position is represented in FIG. 2A by an array of four squares. These are the switching elements or pie sections. The dark lines 68A, 74A, etc. represent conductors, and the dark dots V15, V49, etc. represent via holes connecting the conductors of FIG. 2B with the conductors or square contacts of FIG. 2A. The four square key contact areas for each key position are electrically insulated from each other. The upper right-hand square, or pie position 8, represents the eight bit; the lower right-hand square, or pie position 4, the four bit; the upper left-hand square, or pie position 2 the two bit; and the lower left-hand square or pie position 1, the one bit position. The upper right-hand square of each key position is wired to either output pin 68 or 78. The lower right-hand square of each key position is wired to either output pin 64 or 74. The upper left-hand square of each key position is wired to either output pin 62 or 72, and the lower left-hand square of each key position is wired to either output pin 61 or 71. Output pin 63 is wired to pad 73 which is held in continuous contact with the voltage plane or elastic diaphragm. Table 1 shows the interconnection performed by each via hole V-1 through V-57. The bottom connection column refers to the conductor on the bottom, that is in FIG. 2B. The top connection column represents the conductor or the square pie section to which the via hole interconnects the related bottom conductor. The top connection column is interpreted as follows: Where the via hole are starred as is V-13, V-16, etc., the top connection is to a conductive line such as 62a, 72a, 71a, etc. The other via holes are connected to one of the pie positions at each key location: for example, V-1 is connected to key position D, pie section 2; via V-2 is connected to key position D pie position 1, and so forth.

TABLE 1

Via Hole Connections, FIG. 2.

Top Bottom Via Hole Connection Connection (Line or (Line) pie section) V1 8D2 72b V2 8D1 71b V3 8B2 72b V4 8B1 71b V5 8Z2 72b V6 8Z1 71b V7 8N2 72b V8 8N1 61b V9 8B4 74b V10 8Z4 74b V11 8M2 72b V12 8M1 61b V13* 62a 62b V14 872 62b V15 871 61b V16* 72a 72b V17 882 72b V18 881 71b V19* 71a 71b V20 892 72b V21 891 61b V22 8M8 68b V23 888 68b V24 898 68b V25 8E2 62b V26 8E1 71b V27* 62a 62b V28 842 72b V29 841 71b V30* 62a 62b V31* 72a 72b V32 852 72b V33 851 61b V34* 71a 71b V35 862 62b V36 861 71b V37 8E4 64b V38 844 64b V39 854 64b V40 864 64b V41 8R2 62b V42 8R1 61b V43 812 72b V44 811 61b V45* 72a 72b V46* 62a 62b V47 822 62b V48 821 71b V49* 71a 71b V50 832 62b V51 831 61b V52 8R4 64b V53 818 78b V54 828 78b V55 824 74b V56 838 78b V57 834 74b

Referring further to FIG. 2A and 2B, in connection with Table 2, below, the output code for the key board of FIG. 2 will be explained. A 16-key key board is shown having hexidecimal output values zero through F. The various keys are 8B, 81, 82, 83, 84, 85, 86, 87, 88, 89, 8Z, 8N, 8D, 8M, 8E, 8B. The binary value appearing at the output pins 6Z1-678, is shown in the column entitled Binary Value of Output. Thus, a zero in the 8 column indicates a positive logic on pin 78, a 1 in the 8 column represents a positive logic on pin 68, a zero in the 4 column of the table indicates a positive logic on pin 74, a 1 in the 4 column indicates a positive output on line 64, a zero in the 2 column represents a positive logic level on output pin 72, a 1 in the 2 column represents a positive logic level on pin 62, a zero in the one column represents a positive logic on output pin 71, and a 1 in the one column represents a positive logic on output pin 61.

Thus, by depressing the D key to bring the elastic diaphragm voltage plane into contact with switch array 8D, the hexidecimal output code of zero will be detected as positive logic level on output pins 71, 72, 74, and 78, and negative logic level on output pins 61, 62, 64, and 68. Similarly, by bringing the key array 85 into contact with the voltage plane, a hexidecimal 5 output is detected as a positive logic on output pins 64, 61, 78 and 72.

TABLE 2

Output Code for Keyboard of FIG. 2.

Binary Value of Output Key Hexidecimal 8 4 2 1 __________________________________________________________________________ 8B 0 0 0 0 0 81 1 0 0 0 1 82 2 0 0 1 0 83 3 0 0 1 1 84 4 0 1 0 0 85 5 0 1 0 1 86 6 0 1 1 0 87 7 0 1 1 1 88 8 1 0 0 0 89 9 1 0 0 1 8Z A 1 0 1 0 8N B 1 0 1 1 8D C 1 1 0 0 8M D 1 1 0 1 8E E 1 1 1 0 8R F 1 1 1 1 __________________________________________________________________________

it is thus apparent from the above described embodiment of the invention, that the desired hexidecimal output code is produced directly at the output pins 61 through 78. Proceeding now to FIG. 2C, a description will be given of the circuitry required for rollover protection and strobing. Rollover protection is defined as the detection of the simultaneous depression of two keys. Strobing is defined as the detection of a contact closure occurring at each of the pie positions in a given key array. Referring now to FIG. 2C, the output pins 61 through 78 of FIGS. 2A and 2B are shown. The logic of FIG. 2C may be physically located on logic card 55 (FIG. 5). Output pin 61 is connected to Exclusive OR 11. Output pin 71 is connected to Exclusive OR 11 and AND 16. Output pin 62 is connected to Exclusive OR 12. Output pin 72 is connected to Exclusive OR 12 and AND 17. Output pin 64 is connected to Exclusive OR 13. Output pin 74 is connected to Exclusive OR 13 and to AND 18. Output pin 68 is connected to Exclusive OR 14. Output pin 78 is connected to Exclusive OR 14 and AND 19. The outputs of Exclusive OR's 11 through 14 are connected to AND 15, the output of which is connected to AND's 16 through 19. The inputs to AND 15 are satisfied such that there is a positive logic output therefrom only if the output of each Exclusive OR 11 through 14 is positive. This occurs only when one and only one pin of each the following pairs of outputs pins are positive: 61 and 71, 62 and 72, 64 and 74, and 68 and 78. Thus, a positive output from AND 15 indicates that one and only one key on the key board of FIG. 2A has been depressed. The voltage levels on pins 56-59 are decoded directly to the binary values of Table 2.

Referring now to FIG. 3, the switch card array for a ten key keyboard utilizing a three out of fourteen code and the associated logic for strobe and roll-over protection will be described. The various pie sections A, B, and C for the various switch key locations 90 through 99 are wired by double-sided wiring, described above, to the various output pins 2A0 through 2C3. For sake of simplicity, only the switch arrays 90-99 of the ten key numeric portion of a much larger keyboard is shown, while the logic for the full keyboard is shown. The connections from the various keys 90-99 to the output locations 2A0-2C3 are shown in heavy and dotted lines: the heavy lines being on one side of said switch card and the dotted lines on the other side. It will be apparent to those skilled in the art, that various other wiring schemes may be utilized to connect the various pie sections A, B, and C to the output pins 2A0-2C3. The heavy dots at the connection of dotted lines to solid lines or at the connection of dotted lines to pie sections at the various key locations represent through holes, while the heavy dots between solid lines and the pie sections merely indicate connections between the land pattern conductors and the pie sections which are on the same side of the switch card. Herein, all of the output pin locations 2A0 through 2C3 are connected to positive voltage. The elastic diaphragm is at ground voltage, herein, and is shown as element 50A, diagrammatically.

The roll-over protection logic, as will be described more fully hereinafter, comprises inverters 431 through 444, AND circuits 451 through 464, OR circuits 465 through 467, and AND circuit 468. As will be apparent more fully hereinafter, the 3 of 14 output code generated by actuating one of the keys at key positions 90-99 appears directly at output pins 2A0 to 2C3, while a signal at pin 470 indicates that only one key has been actuated, and that all of the pie sections of that key have made contact with diaphragm 51A, thus signaling that a valid code exists at output pins 2A0-2C3.

First, the output code generated by the various keys 90-99 at output pins 2A0-2C3 will be described, followed by description of the strobe and roll-over protection circuitry of FIG. 3.

First it should be noted that the A pad of each key 90-99 is connected to one and only one of output pins 2A0-2A4. The B pad of each key location 90-99 is connected to one and only one of output pins 2B0-2B4. And finally, the C pad at each key location 90-99 is connected to one and only one of output pins 2C0-2C3. Thus, actuation of key 90 causes a positive logic signal to appear at output pin 2B2, and 2A4, and 2C0. The following Table 3 summarizes the connection between the various pie or switch locations A, B, and C of each key (or switch array) to output pins 2A0-2C3.

TABLE 3

Summary of Connections: Key Locations to Output Pins for FIG. 3

Key Location Pie Section or Output Switch Location 90 90A 2A4 90B 2B2 90C 2C0 91 91A 2A1 91B 2B1 91C 2C0 92 92A 2A1 92B 2B2 92C 9C0 93 93A 2A1 93B 2B3 93C 2C0 94 94A 2A2 94B 2B1 94C 2C0 95 95A 2A2 95B 2B2 95C 2C0 96 96A 2A2 96B 2B3 96C 2C0 97 97A 2A3 97B 2B1 97C 2C0 98 98A 2A3 98B 2B2 98C 2C0 99 99A 2A3 99B 2B3 99C 2C0

Thus, from Table 3 and FIG. 3, it becomes apparent that actuation of key 90 gives an output code comprising positive logic signals at output pins 2A4, 2B2, 2C0. Similarly, actuation of key 94 causes an output code to appear in the form of contact closures at pins 2A2, 2B1, and 2C0.

Referring again to FIG. 3 the strobe and roll-over protection circuitry will be described. Output pin 2A0 is connected to inverter 431, and to AND circuits 452 through 455.

Output pin 2A1 is connected to inverter 432 and AND circuits 451, 453, 454, and 455. Outpin pin 2A2 is connected to inverter 453 and to AND circuits 451, 452, 454, and 455. Output pin 2A3 is connected to inverter 434 and to AND circuits 451, 452, 453, and 455. Output pin 2A4 is connected to inverter 435, and to AND circuits 451 through 454.

Output 2B0 is connected to inverter 436, and to AND circuits 457 through 460. Output pin 2B1 is connected to inverter 437 and to AND circuits 456, 458, 459, and 460. Output pin 2B2 is connected to inverter 438, and to AND circuits 456, 457, 459, and 460. Output pin 2B3 is connected to inverter 439, and to AND circuits 456, 457, 458, and 460. Output 2B4 is connected to inverter 440, and to AND circuits 456 through 459.

Output pin 2C0 is connected to inverter 441 and to AND circuits 462 through 464. Output pin 2C1 is connected to inverter 442 and to AND circuits 461, 463, and 464. Output pin 2C2 is connected to inverter 443, and to AND circuit 461, 462, and 464. Output pin 2C3 is connected to inverter 444, and to AND circuits 461 through 463.

Inverter 431 is connected to AND circuit 451, inverter 432 to AND 452, inverter 433 to AND 453, inverter 434 to AND 454, inverter 435 to AND 455, inverter 463 to AND 456, inverter 437 to AND 457, inverter 438 to AND 458, inverter 439 to AND 459, inverter 440 to AND 460, inverter 441 to AND 461, inverter 442 to AND 462, inverter 443 to AND 463, and inverter 444 to AND 464. The inputs to OR 465 are the outputs of ANDs 451 through 455, the inputs to OR 466 are the outputs of ANDs 456 through 460, and the inputs to OR 467 are the outputs of ANDs 461 through 464. The outputs of OR circuits 465 through 467 are fed to AND circuit 468, the output of which appears at pin 470. A signal at pin 470 indicates strobe and no roll-over.

Referring now to FIG. 4A, a description will be given of a keyboard and logic for generating an EBCDIC code wherein each pie position of each key determines two bits in the output code according to the following table:

TABLE 4

Output Code and Wiring for EBCDIC Keyboard of FIG. 4A

Key Output Pin Locations for Pad Output Code Position A B C D A B C D 12 34 56 78 __________________________________________________________________________ 20 1A3 1B3 1C0 1D0 11 11 00 00 21 1A3 1B3 1C0 1D1 11 11 00 01 22 1A3 1B3 1C0 1D3 11 11 00 10 23 1A3 1B3 1C0 1D3 11 11 00 11 24 1A3 1B3 1C1 1D0 11 11 01 00 25 1A3 1B3 1C1 1D1 11 11 01 01 26 1A3 1B3 1C1 1D2 11 11 01 10 27 1A3 1B3 1C1 1D3 11 11 01 11 28 1A3 1B3 1C2 1D0 11 11 10 00 29 1A3 1B3 1C2 1D1 11 11 10 01 __________________________________________________________________________

the above table, giving the output code and wiring scheme for the EBCDIC keyboard of FIG. 4A, may be correlated with FIG. 4A in the following manner. Actuation of the key which brings switch array 20 into contact with ground plane or elastic diaphragm 51B causes a positive logic signal to appear at output pin locations 1A3, 1B3, 1C0, and 1D0. This gives an output code of 11110000. The wiring from key 20 to said output pins is by double-sided wiring, as shown in FIG. 4A, where the switch locations or pie positions and the wiring on the same side of the switchcard as said pie positions are shown in solid lines, with the dark dots representing via holes between said conductors and pie positions to the dotted lines representing conductors on the opposite side of said switch card. Thus, pie section B of switch array 20 is connected by a solid line to output pin 1B3, pie sections A and D are connected by double sided wiring (shown by dotted and solid lines) to pads 1A3, and 1D0 and pie section C is connected by single side wiring to its output pin 1C0.

While actuation of a given key results in direct generation of sixteen bit code at output pins 1A0-1D3, herein the code at said pins is further decoded to give an eight-bit output code at pins 310, 320, 330, 340, 350, 360, 370, and 380 of FIG. 4A. The same decoding logic for giving the eight-bit output code is utilized for the strobe and rollover protection in the manner to be described hereinafter. Referring again to the TAble 4 in connection with FIG. 4A, output code bits 1 and 2 are determined by the state of output pins 1A0, 1A1, 1A2, and 1A3. Output code bits 3 and 4 are determined by the state of output pins 1B0-1B3. The bits 5 and 6 of the output code are determined by the state of output pins 1C0-1C3, and the state of bits 7 and 8 of the output code are determined by the condition of output pins 1D0-1D3. For each set, that is, the A, B, C, or D set of pins, the associated two bits in the output code will be zero if the zero (i.e., 1A0, 1B0, 1C0, or 1D0) pin is at a positive logic level, or "on." if the 1 pin is on, the associated output code bits will be 01. If the 2 pin is on, the associated output code bits will be 10. And finally, if the 3 output pin is on, the associated output code bits will be 11. In the above manner, output pins 1A0-1A3 on the switchcard control the state of output pins 310 and 320 representing bits 1 and 2, respectively. Bits 1 and 2 will be 00 if 1A0 pin is on, 01 if 1A1 pin in on, 10 if the 1A2 pin is on, and 11 if the 1A3 pin is on.

As in FIG. 3, FIG. 4A shows the switch array or key locations for only 10 keys of a much larger keyboard, but the logic shown is for the entire keyboard.

Referring now to FIG. 4A, the manner in which the output pins 1A0-1D3 are decoded to provide the rollover protection, strobe, and the eight-bit EBCDIC code will next be described. The Data Selector/Multiplexor, DS/M 211 shown in FIG. 4A is shown in greater detail in FIG. 4B and will be described hereinafter. Suffice it to say at this time, that the outputs of any DS/M will be negative if and only if one of the four inputs is positive. The OR inverters, OI will have a positive output when either but not both of its inputs is positive. An inverter I inverts the signal at the input. An AND inverter AI gives a negative output when all of its inputs are positive. A single shot SS gives a timed positive output whenever its input goes positive. A negative OR inverter -OI gives a negative output when one but not both of its inputs are negative. Parity generator PG gives a positive output when an even number of its inputs are positive, and a negative output when an odd number of its inputs are positive.

Proceeding now with a description of the logic flow of FIG. 4A, output pin 1A0 is connected to DS/M 211. Output pin 1A1 is connected to DS/M 211 and OI 272. Output pin 1A2 is connected to DS/M 211 aNd OI 271. Output pin 1A3 is connected to DS/M 211, OI 271, and OI 272. Output pin 1B0 is connected to DS/M 212. Output pin 1B1 is connected to DS/M 212 and OI 274. Output pin 1B2 is connected to DS/M 212 and OI 273. Output pin 1B3 is connected to DS/M 212, OI 273, and OI 274. Output pin 1C0 is connected to DS/M 213. Output pin 1C1 is connected to DS/M 213 and OI 276. Output pin 1C2 is connected to DS/M 213 and OI 275. Output pin 1C3 is connected to DS/M 213, OI 275, and OI 276. Output 1B0 is connected to DS/M 214. Output pin 1D1 is connected to DS/M 214, and OI 278. OUtput pin 1D2 is connected to DS/M 214 and OI 277. Output pin 1D3 is connected to DS/M 214, OI 277, and OI 278.

Herein, all of the output pins 1A0 through 1D3 are connected to positive voltage.

The output of DS/M 211 is inverted by I 215 and fed to AI 219. The output of DS/M 212 is inverted by I 216 and fed to AI 219. The output of DS/M 213 is inverted by I 217 and fed to AI 219. The output of DS/M 214 is inverted by I 218 and fed to AI 219. Thus, a negative output of any DS/M is inverted and appears as a positive input to AI 219. The output of AI 219 will be positive, therefore, when one and only one of the A pins, one and only one of the B pins, one and only one of the C pins, and one and only one of the D pins are at a positive logic level. The output of AI 219 is fed to single shot 220, the output of which appears on rollover protection line 210, which line 210 has a positive logic level when one and only one of the keys 20-29 are in contact with the ground plane or elastic diaphragm 51B.

The output of single shot 220 is also fed bit gates to AI 301-308. The output of OI 271 is fed to AI 301, of OI 272 to AI 302, of OI 273 to AI 303, of OI 274 to AI 304, of OI 275 to 305, of OI 276 to AI 306, of OI 277 to AI 307, and of OI 278 to AI 308. Thus, the various bit gates 301-308 have a positive output when one and only one key has been made as signaled on line 210 and the corresponding bits 1 through 8 has been decoded from the output pins 1A0-1D3 by the OR inverters 271-278. The output of the bit gates, AI's 301-308 are held in the corresponding bit latches, comprising a -OI and an AI, until the latches are restored by a signal at pin 300. Similarly, rollover protection is held in the bit latch comprising -OI 230 and AI 260 to hold output pin 390 at a logic level indicating strobe and inviting the using logic (not shown) to accept the output code appearing on pins 310-380.

Thus, the output of single shot 220 is fed to -OI 230, thence to AI 260, and strobe output pin 390. The output of AI 301 is fed to -OI 311, thence to AI 321 and to bit 1 output pin 310. The output of AI 302 is fed to -OI 312, thence to AI 322 and to bit 2 output pin 320. The output of AI 303 is fed to -OI 313, thence to AI 323 and to bit 3 output pin 330. The output of AI 304 is fed to -OI 314, thence to AI 324 and to bit 4 output pin 340. The output of AI 305 is fed to -OI 315, thence to AI 325 and thence to bit 5 output pin 350. The output of AI 306 is fed to -OI 316, thence to AI 326 and thence to bit 6 output pin 360. The output of AI 307 is fed to -OI 317, thence to AI 327 and thence to bit 7 output pin 370. The output of AI 308 is fed to -OI 318, thence to AI 328 and thence to bit 8 output pin 380. The output of AI's 321-328 are also fed to parity generator 329, the output of which appears at pin 331. The restore line signal appearing at 300 is fed to AI 260, and AI 321-328. The output of AI 260 is fed back to -OI 230. The output of AI 321 is also fed back to -OI 311. The output of AI 322 is also fed back to -OI 312. The output of AI 323 is also fed back to -OI 313. The output of AI 324 is also fed back to -OI 314. The output of AI 325 is also fed back to -OI 315. The output of AI 326 is also fed back to -OI 316. The output of AI 327 is also fed back to -OI 317. And, the output of AI 328 is also fed back to -OI 318.

With the logic above described and shown in FIG. 4A, a signal appearing at output pins 1A0-1D3 representing the closure of contacts comprising the pie sections of a given key location 20-29 and the elastic diaphragm ground plane 51B, are decoded to an eight-bit code at pins 310-380, and roll-over protection and strobe signals are generated at lines 210 and 390.

Referring now to FIG. 4B, a more detailed description will be given of Data Selector/Multiplexor 211 of FIG. 4A. The other DS/M's 212-214 are similarly wired to perform similar functions, as will be apparent to those skilled in the art. Referring now to FIG. 4B, a negative signal appears at output line 261 when one and only one of pins 1A0-1A3 are connected to ground by closure of the corresponding switch. Said switches are shown to represent the pie sections A at the various switch arrays 20-29. Pin 1A0 is connected to inverter 221, pin 1A1 is connected to inverter 222, pin 1A2 is connected to inverter 223, and pin 1A3 is connected to inverter 224. The connections to inverters 221-224 represent the four input lines shown at the inputs to DS/M211 through 214 in FIG. 4A. Not shown in FIG. 4A are the wiring locations E, E0, E15, Wiring locations E7, E11, E13, and E14 are held at a positive voltage through resistance R1. On the other hand, wiring locations E, E0-E6, E8-E10, E12, and E15 are tied to ground.

The ground voltage appearing at wiring location E is inverted by I 229 and fed to AND circuits 231-246. This signal would serve to enable all of said AND circuits 231-246. However, the ground voltage at wiring location E0 is fed to AND 231, thus effectively disabling said AND circuit 231 from operation. Similarly, and for the same function, the ground voltage at wiring location E1 is fed to AND circuit 232, at E2 is fed to A 233, at E3 is fed to AND circuit 234, at E4 is fed to AND circuit 235, at E5 is fed to AND circuit 236, at E6 is fed to AND circuit 237, at E8 is fed to AND circuit 239, at E9 is fed to AND 240, is fed to AND circuit 241, at E12 is fed to AND 243, and at E15 is fed to AND circuit 246. On the other hand, positive voltage at wiring location E7 is fed to AND circuit 238 to enable said AND circuit 238. Similarly, the positive voltage at E11 is fed to AND circuit 242, at E13 is fed to AND circuit 244, and at E14 is fed to AND circuit 245.

The output of inverter 221 is fed along line 252 to AND circuits 231, AND circuit 233, AND circuit 235, AND circuit 237, AND circuit 239, AND circuit 241, AND circuit 246, and AND circuit 245. Also, the output of inverter 221 is fed through inverter 225 and thence along line 253 to AND circuit 232, 234, 236, 238, 240, 242, and 244 and 246.

The output of inverter 222 is fed along line 254 to AND circuits A231, 232, 235, 236, 239, 240, 243, and 244. Also, the output of inverter 222 is fed through inverter 226 along line 255 to AND circuits 233, 234, 237, 238, 241, 242, 245, and 246.

The output of inverter 223 is fed along line 256 to AND circuits 231-234, and 239-242. The output of inverter 223 is also fed through inverter 227 along line 257 to AND circuits 235-238 and 243-246. The output of inverter 224 is fed along line 258 to AND circuits 231-238. Also, the output of inverter 224 is fed through inverter 228 along line 259 to AND circuits 239-246. The output of AND circuits 231-246 are fed to OR circuit 250, the output of which appears at output pin location 261. With the arrangement shown in FIG. 4B, a negative signal will appear at output pin 261 when one and only one of the inputs to inverters 221-224 is positive.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in forms and details may be made therein without departing from the spirit and scope of the invention.