Circuit arrangement for an input keyboard

A keyboard switch matrix has a plurality of column and row wires and switches having only two poles and no interconnecting diodes for selectively connecting one of said columns to one of said rows. Associated with each column and row wire is a flip-flop having a set input connected to the wire and an electronic switch for each flip-flop connecting a flip-flop output to the set input. The outputs of the row flip-flops are connected to a NOR-gate, the output of which is connected to a control input of the electronic switches associated with the column flip-flops and also to a second set input of the column flip-flops. The output of the NOR-gate is further connected to a control input of the electronic switches associated with the row flip-flops through an inverter. Reset inputs of the column flip-flops are connected to the NOR-gate output through a differentiation circuit which is triggered by a negative pulse edge. A second NOR-gate has its inputs connected to the column wires and provides an output to a differentiation circuit which is triggered by a positive pulse edge. The output of the differentiation circuit is connected to reset inputs of the row flip-flops. Thus, the geometric position of the actuated keyboard switch is stored in the respective row and column flip-flops, and code signals corresponding to said position are provided at the outputs of said flip-flops.

BACKGROUND OF THE INVENTION 
This invention relates in general to a circuit arrangement for an input 
keyboard and more particularly to an electronic circuit for a keyboard 
switch matrix, the switches of which have only two poles and no 
interconnecting diodes. 
DESCRIPTION OF THE PRIOR ART 
Electronic equipment is controlled in many cases via an input keyboard 
which, as a rule, consists of key switches arranged in rows and columns. 
As such equipment there are known, e.g., electronic calculating machines 
(computers), electronic pocket calculators or remote control arrangements 
for e.g., phonographs, radio or television receivers. The key switches, 
when actuated, serve to establish electrical connections between input 
leads which may be associated with the aforementioned rows and columns. 
Thus, in the technical journal "IBM Technical Disclosure Bulletin", 
October 1966, pp 532/33 there is described a keyboard circuit for 
data-processing systems in which the information, via the just depressed 
key switch, is represented in a three-out-of-eight code. The key switches 
as such, are simple bipolar switches acting as make contacts. Each such 
key switch is associated with four decoupling diodes connecting it with 
four of nine input leads of the data-processing system which, in turn, and 
with the aid of sampling signals, continuously interrogates the input 
keyboard in order thus to ascertain a depressed key switch. Accordingly, 
this arrangement operates in a dynamic technique. 
In the technical journal "Electronic Engineering", September 1976, page 36 
there is described another data-processing system whose input keyboard 
cooperates with the integrated circuit MC 14419 as described in the data 
book published by the firm of Motorola "Semiconductor Data Library", 
Volume 5, Series B, 1976, pp 5-201 to 5-204. From FIG. 4 of this 
publication it may be seen that the key switches must be equipped either 
with double contacts for connecting a supply voltage to the corresponding 
row or column lead, or that otherwise a key switch may be provided having 
a single contact when being connected to the respective column or row lead 
via two diodes. It is obvious that such an embodiment or such a circuitry 
of the key switches is more expensive than those of the key switches 
employing a single contact and mentioned in the aforementioned literature. 
The integrated circuit MC 14419 referred to, contains a two-out-of-eight 
encoder with a subsequently arranged code converter for a binary-coded 
decimal (BCD)-code. This circuit likewise operates in a dynamic technique, 
i.e. there is provided a timing signal oscillator for controlling the 
operating sequences in forming the code. 
From a further data sheet published by Motorola Semiconductors, No. E 175, 
June 1976, there has become known the integrated circuit MC 14422 P 
realized in CMOS-technology, for remote control transmitters, which 
likewise operates in a dynamic technique and, for this purpose, contains a 
scanning oscillator, a scanning control circuit, and further, additional 
circuits. In this arrangement it is likewise possible to use 
single-pole-key switches. Finally, there is known from "Electronics", 
January 6, 1977, pp 110 to 112 an input keyboard employing single key 
switches in which the depressed key is ascertained with the aid of the 
micro-processor F8, for which the corresponding programme (software) is 
mentioned in the publication. 
Accordingly, the two last-mentioned publications show arrangements which 
solve the keyboard encoding problem by involving an investment which, also 
with respect to integrated circuits, is relatively high Especially the 
last-mentioned publication proposing to use a commercially available 
micro-processor, is not realizable in cases, for example in the case of 
the aforementioned remote control, where, in one integrated circuit there 
is to be accommodated not only the keyboard encoding, but also the 
remaining remote control transmitter circuit. In such a case the keyboard 
encoding must do with as small as possible crystal surface, in order that 
sufficient crystal surface of the integrated circuit will remain to be 
left for the actual function of the remote control transmitter. Especially 
when looked at from this point of view it is rather out-of-the-way to 
provide a micro-processor, because essential parts thereof will remain 
unused. But also the aforementioned dynamic technique is too expensive for 
meeting the given requirement. 
SUMMARY OF THE INVENTION 
According to this invention a circuit arrangement for an input keyboard of 
electronic equipment comprises two-terminal key switches arranged in m 
columns and n rows, with each key switch, upon actuation, directly 
connecting a column lead associated with the respective column, to a row 
lead associated with the respective row, and the circuit arrangement, with 
respect to the columns, transmitting a one-out-of-m code signal and, with 
respect to the rows, a one-out-of-n-code signal, one row flip-flop each 
per row, comprising one reset and one set input which is connected to the 
respective row lead, one first make contact type electronic switch each 
per row flip-flop connecting the set input thereof to the output 
associated with this set input; a first NOR-gate having n inputs which are 
arranged at the output of each row flip-flop associated with the 
respective input; a first differentiating circuit whose input is connected 
to the output of the first NOR-gate, and which is triggered by a 
negatively directed pulse edge; an inverter stage whose input is connected 
to the output of the first NOR-gate, and whose output is connected to all 
control inputs of the first electronic switches; one column flip-flop each 
per column having one reset input and two set inputs not conditioning one 
another of which the first one is connected to the respective column lead 
and the second one is connected to the output of the first NOR-gate with 
the reset input being connected to the output of the first differentiating 
circuit one second make contact type electronic switch each per column 
flip-flop, connecting the first set input thereof to the output associated 
in common with the two set inputs, and whose control input is applied to 
the output of the first NOR-gate; a second NOR-gate having m inputs 
applied to the respective first set input of the column flip-flops; a 
second differentiating circuit whose input is connected to the output of 
the second NOR-gate, and whose output is connected to all reset inputs of 
the row flip-flops, triggered with the aid of a positively directed pulse 
edge, and a highly resistive termination, of each column lead. 
It is an object of this invention to provide a circuit arrangement for 
input keyboards in which it is possible to use key switches having two 
terminals and without having to take additional decoupling measures, and 
in which the crystal surface necessary for the integration, is designed in 
accordance with the non-dynamic, hence the static technique. 
With the circuit according to this invention it is possible to build also 
voluminous input keyboard switch matrices which may contain substantially 
more key switches than the prior art keyboards mentioned hereinbefore 
comprising a maximum of 16 key switches.

DETAILED DESCRIPTION OF THE INVENTION 
For the sake of simplicity and as an example of an embodiment, the block 
diagram according to FIG. 1 shows a three-by-three input keyboard, i.e., 
the number m of the column leads and the number n of the row leads each 
time equals three. The respective key switches 17, 18, 19; 27, 28, 29; 37, 
38, 39 are arranged at each crosspoint of these leads, with these key 
switches, when actuated, directly connecting the corresponding column lead 
to the corresponding row lead. 
The three row leads 1, 2, 3 and the three column leads 7, 8, 9 are 
respectively associated with one row flip-flop and a first electronic 
switch acting as a make contact, or with one column flip-flop and a second 
electronic switch acting as a make contact, respectively. Moreover, the 
column leads 7, 8, 9 are terminated in a highly resistive manner. Relative 
thereto, there are shown in the example of embodiment of FIG. 1 the 
resistors 797, 798, 799 as extending to the zero point of the circuit but 
which, however, may also extend to any other suitable potential. The high 
resistivity with respect to the resistance of the electronic switches must 
be safeguarded in their switched-on states. 
Each of the set inputs 111, 121, 131 of the row flip-flops 11, 12, 13 is 
connected to the corresponding row lead 1, 2, 3 and is applied to the 
respective output 119, 129, 139 via a first electronic switch 14, 15, 16 
each of which are controlled like a make contact, hence which are open 
when in the non-actuated state. Each of these outputs is the output 
associated with the set input, hence the Q-output of the row flip-flops, 
and connected with one of the inputs 171, 172, 173 of the first NOR-gate 
17'. The number of inputs of this gate is equal to the number n of the row 
leads. 
The output 179 of the first NOR-gate 17' is applied, on one hand, to the 
input 181 of the first differentiating circuit 18' whose output 189 
extends to each reset input 715, 725, 735 of the column flip-flops 71, 72, 
73 and, on the other hand, to the input 191 of the inverter stage 19' 
whose output 199 extends to each of the control inputs 143, 153, 163 of 
the first electronic switches 14, 15, 16 and finally to each second set 
input 712, 722, 732 of the column flip-flops 71, 72, 73 as well as to each 
control input 743, 753, 763 of the second electronic switches 74, 75, 76. 
Accordingly, these set and control inputs are all simultaneously 
controlled by the output signal of the first NOR-gate 17'. 
Each column flip-flop 71, 72, 73 has two set inputs not conditioning one 
another. This can be achieved, for example, in that a conventional 
flip-flop, hence for example, an SR storage flip-flop, a JK flip-flop or 
the like is preceded with respect to one input by an OR-gate. Each first 
set input 711, 721, 731 is applied to one column lead 7, 8, 9 each, and, 
via the respective second electronic switch 74, 75, 76 which are likewise 
controlled like a make contact, hence are open when in the non-actuated 
state, applied to the respective output 719, 729, 739 associated with the 
two set inputs, which is the Q-output of the column flip-flop. 
Each of these first set inputs and, consequently, also the column leads 7, 
8, 9 are applied to each time one input of the second NOR-gate 77, the 
number of which is equal to the number m of column leads. The output 779 
of the second-NOR-gate 77 is applied to the input 781 of the second 
differentiating circuit 78 whose output 789 is connected to each of the 
reset inputs 115, 125, 135 of the row flip-flops 11, 12, 13. As the first 
or second differentiating circuit 118' or 78 it is possible, for example, 
to use monostable multivibrators having a short metastable state, with the 
first differentiating circuit 18' only supposed to be triggered by a 
negatively directed pulse edge and the second differentiating circuit 78 
only supposed to be triggered by a positiviely directed pulse edge. 
The output signals in the aforementioned one-out-of-m-code or 
one-out-of-n-code may be taken off at the aforementioned Q-outputs or else 
invertedly in relation thereto, at the Q-outputs 118, 128, 138; 718, 728, 
738 of the row or column flip-flops respectively. 
FIG. 2 shows various waveshapes of signals as appearing during operation of 
the arrangement according to FIG. 1 in a positive logic, and which result 
from the following function description. Relative thereto, it is started 
out from the normal state in which all key switches 17, 27, 37; 18, 28, 
38; 19, 29, 39 are in the non-actuated state. The signals occurring in the 
course of this are shown in FIG. 2 on the left of the vertical solid line. 
The Q-outputs 719, 729, 739 of the column flip-flops 71, 72, 73 each 
conduct an H-signal corresponding to a high potential, c.f. FIGS. 2a, 2b, 
and the Q-outputs 119, 129, 139 each conduct an L-signal corresponding to 
a lower potential, c.f. FIGS. 2c, 2d. Accordingly, one H-signal each is 
applied to the output 179 of the first NOR-gate 17' and to the control 
inputs 743, 753, 763 of the second electronic switches 74, 75, 76 as 
connected thereto, as well as to the first set inputs 711, 721, 731 of the 
column flip-flops 71, 72, 73, c.f. FIGS. 2e 2f so that the second 
electronic switches are closed and one H-signal each is applied to the 
column leads 7, 8, 9, c.f. FIGS. 2e, 2f. The H-signal at the output 179 of 
the NOR-gate 17', inverted into the L-signal, is applied to the control 
inputs 143, 153, 163 of the first electronic switches 14, 15, 16, c.f. 
FIG. 2k, so that these electronic switches are opened and, consequently 
one L-signal each is applied to the row leads 1, 2, 3, c.f. FIGS. 2g, 2h. 
The H-signals at the column leads 7, 8, 9 cause an L-signal to appear at 
the output 779 of the second NOR-gate 77, c.f. FIG. 2m. An L-signal is 
likewise applied to the outputs 189, 789 of the two differentiating 
circuits, c.f. FIGS. 2l, 2n. 
Assuming now that the key switch 28 at the crosspoint of both the column 
lead 8 and the row lead 2 is depressed during the time t. In that case, 
the H-signal of the column lead 8 is applied via the row lead 2 to the set 
input 121 of the row flip-flop 12, and causes it to change states (c.f. 
FIG. 2h). At the Q-output 129 of the row flip-flop 12 the L-signal is 
changed into an H-signal, c.f. FIG. 2d, with this H-signal, via the first 
NOR-gate 17' and the inverter stage 19', closing the first electronic 
switches 14, 15, 16, c.f. FIG. 2k. Moreover, the H-signal at the Q-output 
129 of the row flip-flop 12, inverted into the L-signal via the first 
NOR-gate 17', is applied to the second set inputs 712, 722, 732 of the 
column flip-flops 71, 72, 73 and to the control inputs 743, 753, 763 of 
the second electronic switches 74, 75, 76, thus causing the latter to be 
opened, c.f. FIG. 2i. 
The H-L-signal inversion as appearing upon actuation of the key switch 28 
at the output 179 of the first NOR-gate 17', representing a negatively 
directed pulse edge, serves to trigger the first differentiating circuit 
18', so that this circuit will transmit a short H-pulse, c.f. FIG. 2l, by 
which the column flip-flops 71, 72, 73 are reset via their reset inputs 
715, 725 735, thus causing the Q-outputs thereof each to assume one 
L-signal, c.f. FIGS. 2a, 2b. 
Via the still depressed key 28 and the closed first electronic switch 15, 
the H-signal at the Q-output 129 of the row flip-flops 12 is applied to 
the first set input 721 of the column flip-flop 72, so that this 
flip-flop, upon disappearance of the reset signal at its reset input 725, 
is reset and, consequently, the Q-output 729 thereof again assumes an 
H-signal, c.f. FIG. 2b. Accordingly, of the column leads 7, 8, 9 only the 
column lead 8 still conducts an H-signal, because owing to the opening of 
the electronic switches 74, 75, 76, and across the highly resistive 
terminals 797, 779, the column leads 7, 9 have discharged and, 
consequently, conduct an L-signal c.f. FIG. 2e. Considering that the 
column lead 8 is now the only one to which an H-signal continues to be 
applied, c.f. FIG. 2f, the L-signal is maintained at the output 779 of the 
second NOR-gate 77, c.f. FIG. 2m. 
Releasing the key 28 at the end of the period of time t causes the H-signal 
to disappear at the column lead 8 owing to a discharge across the highly 
resistant termination 798, c.f. FIG. 2f, and at the output 779 of the 
second NOR-gate 77, the L-signal is changed into an H-signal, c.f. FIG. 
2m, with this L-H-signal inversion representing a positively directed 
pulse edge, triggering the second differentiation circuit 78, so that the 
latter will transmit a short H-pulse, c.f. FIG. 2n. Via the reset inputs 
115, 125, 135, this pulse resets the row flip-flops 11, 12, 13 to their 
original states, so that the Q-outputs 119, 129, 139 re-assume the 
L-signal, thus re-establishing the original normal state. 
The circuit arrangement according to this invention which, as the 
description has shown, works without a timing signal oscillator (clock 
pulse oscillator), can be realized in a particulary favorable way by 
employing the well-known CMOS-technology. In this case it lends itself in 
a particularly favorable way for being used in ultrasonic or infrared 
remote control units for phonographs, radio or television receivers. For 
other applications, the circuit arrangement according to this invention, 
however, may also be realized with the aid of other integrating 
technologies. For this purpose it is suitable, for example, to employ the 
MOS-technology, hence circuits employing insulated gate field-effect 
transistors of the same channel conductivity type, or else bipolar 
circuits, especially integrated injection logic (I.sup.2 L) circuits. 
It will be evident to the person skilled in the art, that it is within the 
scope of this invention, by maintaining the same mode of operation, to 
change over from the positive logic as chosen in the example of 
embodiment, to a negative logic, in which case then, in the conventional 
way, the type of the employed gates, differentiating circuits and 
electronic switches, will have to be chosen in a correspondingly dual way. 
Moreover, in such a case, both the controlling of the flip-flops and the 
use of their outputs will have to be modified accordingly, with 
additionally required signal inversions having to be provided for by 
inserting further inverter stages at the corresponding points. 
While we have described above the principles of our invention in connection 
with specific apparatus it is to be clearly understood that this 
description is made only by way of example and not as a limitation to the 
scope of our invention as set forth in the objects thereof and in the 
accompanying claims.