It is an object of the present invention to provide computer apparatus that enables several operators to combine to use a central computer. This is in contradistinction to ^' conventional time-sharing wherein a particular computer is used for two or more concurrent operations; the computer operates momentarily to fulfil one purpose, then another, returns to the first, and so on in succession until the operations are completed. This activity is performed at high speed according to a strict sequence, each independent operation being executed as a series of finite steps. Usually such time-sharing computer apparatus comprises a main frame, peripherals and a series of remote terminals sending data to and receiving data from the main frame.

According to the present invention, computer apparatus comprises a central computer having a data input port, means connecting two or more remote chord keyboards to the input port, means for identifying with each respective keyboard alpha-numeric and like

character data and command instructions generated by operation thereof and received through the input port; the central computer being programmed to process and combine the character data from the keyboards in accordance with the commands and to output resultant in ormation for display in common by video and/or audio display means.

The remote keyboards, which may be connected to the central computer by cable, infra-red, ultra-sonic or any other suitable data link, serve to transmit data to the central computer, a resident programme therein processing and combining the various inputs of data, to produce information for display in common. Data thus flows from each operator, via the keyboards and data link to the central computer from whence processed information is passed to the display means; data returns to the operators visually or aurally. The data link is essentially one-way.

The remote chord keyboards are essentially touch- type keyboards; preferably of the kind described in

United States Patent Specification No.4360892 wherein a chord of a combination of between one and five keys is operated to generate a given alphabetic, numeric or punctuation character or command. Chord keyboards have the advantages of simplicity of construction and

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use and a 'touch-type' facility that uniquely enables the keyboard to be used as an alpha-numeric character input device for video games or generally as a computer input device. By touch-typing a player or user is enabled to watch a display and simultaneously input character data and commands at a fast rate so that, for example, word-based games can be played "against the clock" or competitively with other players at high input speeds. Specific keys may also be designated to give movement instructions e.g. up, down, left and right instructions for a cursor or the like.

Computer apparatus in accordance with the invention includes home micro-computers or video game devices both using a domestic. television receiver as the video and audio display means.

In a preferred application of the invention up to four of the remote keyboards can be connected to a home or micro-computer whereby, according to the programme loaded into the computer, a number of different operators can operate the computer in independent or interactive modes. By this means games, such as word games, can be played with several players. For classroom use, teaching programmes may be employed wherein several students can

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simultaneously operate the computer.

In an embodiment of the invention each keyboard is arranged to produce discrete analog voltage signals uniquely corresponding to each operated key or keys-combination and analog-to-digital converter means are connected between the input port and the central computer. Such an arrangement is not susceptible to radio interference as are more conventional digital remote key pads. In another embodiment of the invention, the remote chord keyboard comprises a restricted number of key-operated switches connected to switch passive electrical components arranged in a network wherein interconnections of switches and components and the individual values of the components are such that operation of any individual switch or operation of each possible combination of between two and all the switches produces a unique variance in a given parameter of the network; whereby discrete analog signals uniquely corresponding to each operated key or keys combination can be produced.

Preferably the key-operated switches are connected to switch a ladder network of resistors arranged so that each switch operates to switch a different parallel resistor of the network, the

value of the resistors being such that the network has a different resistance for each operated key or keys-combination.

The above and other features of the invention are illustrated by way of example in the drawings, wherein:-

Fig. 1 is a block diagram of computer apparatus in accordance with the invention;

Fig. 2 is a more detailed plan of one of the remote keyboards for the apparatus of Fig. 1;

Fig. 3 is a circuit diagram for a resistor ladder network for the keyboard of Fig. 2;

Fig. 4 is a circuit diagram of an A-D converter interface; and Fig. 5 is a block diagram of the converter of Fig. 4.

As shown by Fig. 1, computer apparatus comprises four identical, six key, chord keyboards 1,2,3 and 4 each respectively connected by lines 5,6,7,and 8 to an analog input port 9 for a four channel analog-to- digital converter 10. A bidirectional data port 11 connects the A-D converter to a similar port 12 for a central or host computer 13, the output of which is connected to a video and audio display means 14. In an example, the central computer 13 was a BBC

(Trade Mark) model B micro-computer connected to a domestic television receiver, forming the video and audio display means 14; the BBC micro-computer having an inbuilt four channel A-D converter. By these means up to five operators, one using the computer's own keyboard, can be accommodated at the same time. The computer can be used in two modes, an interactive one wherein each operator interacts with the other operators to contribute to the same programme e.g. multiplayer games or an independent one wherein each operator separately inputs character data and commands e.g. in teaching aids whereby effective use of a single micro-computer can be extended to from one to say, five students, each programming and operating the computer independently and receiving data from an assigned portion of the display.

Fig. 2 shows, in more detail, one remote keyboard 1, it is conveniently, part of the portable word processor described in United States Patent Specification No.4360892 and it consists of a casing 15 generally in the form of a truncated square pyramid having an essentially planar rear face 16 and four keys E, 0, S and U carried by the opposite front face 17; the keys are intended to be operated by the index, middle

ring and little fingers of an operator's right hand. A side face 18, to the left of the casing, carries two further keys SPACE and CONTROL; each intended to be -used by an operator's thumb. Output lead 5 terminated by a suitable plug forms the data link to the input port 9. The key references are the character or command generated by operation of that key alone. Other characters or commands are generated by operation of chords of keys e.g. SPACE + O + S generates the character 'Y- or '?' (if shifted to the numerals and punctuation register) and CONTROL + 0 + S generates the command 'Shift to numerals and punctuation register'; similarly, SPACE + E generates 'I' or '2' and CONTROL + E generates the command 'INSERT'.

A suitable circuit for the remote keyboards is shown in Fig. 3 and consists of an "R-2R" resistor network wherein six resistors (all of value X Ohms) are serially connected to one line a of the network. Six resistors (all of value 2X Ohms) are each connected in parallel between line a. and the movable contact of one of six switches CONTROL, SPACE, E, 0, S and U. Each switch is a micro-switch of the normally closed type, the NC contacts of all the switches being connected to a second line b of the

network whilst the other contacts of each switch are connected to a third line c of the network. Instead of a switch, a solid state device such as a CMOS gate (that is a gate having a low output resistance in comparison with the 2X Ohm resistors) could be used. A further resistor of value 2X Ohms is connected between the end of the serial resistors on line a and line c_. Line b is held at one voltage Vref and line c_ at another voltage, in this case common i.e.

10 Ov; the output signal I/P is present on line a..

The operation of the network is such that operation of each of the six switches CONTROL, SPACE, E, 0, S and U, from its normally closed position, produces an output signal Vref between lines a and c

15. that is binarily weighted for the position of that switch in the network. The output signal for individual operation of each switch can be tabled as below:-

Switch operated Output signal Binary weighting

2θ None 0 000000

CONTROL Vref h 100000

SPACE Vref h 010000

U (least significant Vref 64 000001

25 digit)

Clearly, operation of each possible combination of switches will produce a unique output signal, for example operation of keys SPACE, O, S and U produce the output signal (23/64) Vref (010111); which can generate the letter 'M ^* or the numeral '8'.

In a preferred form, a further resistor d, of value 2X Ohms, is connected between the end of the serial resistors R on lines a. and b. The effect of resistor d is to ensure that an offset voltage equal to one half L.S.D. (L.S.D. being the least significant digit, i.e. in this example switch U) is added to all voltages thus easing decoding of the signals produced by the keyboard. Each code spans its fraction of the reference voltage from V - Vref/128 to V + Vref/128, where V is the nominal value. With resistor d in circuit, the output signal for individual operation of each switch is as previously, but with the addition of one half L.S.D. Thus, operation of keys SPACE, 0, S and U produce the output signal ratio (5 + 3 + 2 + 1 + ) = 11 .

Conveniently, the code first described in United States Patent Specification No.4360892 can be used in the assignment of particular characters and commands to particular combinations of switch operations; of course other codes could be used.

Capacitor C is connected between line a and line c to suppress superfluous waveforms, such as switching spikes, in the output.

Although a six switch network has been described, other networks with less or more switches could be employed although the accuracy and availability of resistors will provide a practical upper limit to the number of switches of about eight.

In the described example, each of the data links 5, 6, 7 and 8 have three conductors for the three lines a, b and c_ to connect the respective keyboard to the central computer.

As already mentioned, the BBC model B micro¬ computer can accept analog signals as input data and can provide a suitable ref rence voltage (Vref). Returning to Fig. 1, the A-D converter 10 translates an input voltage (input 1, input 2, input 3 or input 4) .into 8 bit data for processing by the host computer. As described above the input voltage is directly related to the pattern or chord of keys pressed. The 8 bit bidirectional port 11 receives instructions from the host computer 13, selects the channel number and starts the A to D conversion. When the conversion is complete, port 11 sets a bit to indicate to the computer 13

that data is available for collection. The host computer may then sample regularly (e.g. every lO milliseconds) or only collect data when conversion is complete. Repeated .scanning of all four channels via the single 8 bit port, enables data to be collected and the processing of this data allows the current status of any keyboard to be ascertained. With a six switch network as described above only 6 bits are required and the software of the resident programme is arranged to discount the unwanted 2 bits from the A-D converter. Data is identified with a particular input by virtue of the resident programme controlling the CPU to scan the input channels to the A-D converter and causes the CPU to pre-assign memory locations. When a key is operated on any one keyboard the programme causes the CPU to remember that key and all subsequent keys which are operated on that keyboard until all the operated keys are released. The stored key operations are then interpreted by the programme according to the current state, i.e. SHIFT, set in the programme to cause the CPU to either alter the state of the programme as the result of a command or to generate an output character, or both. Fig. 4 shows a circuit for an interface for use

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with micro-computers that do not have an analog input port, such as a Commodore VIC 64 Home Computer; the interface is based on an NEC D7002C A/D converter of which a block diagram is shown in Fig. 5.

The operation of the circuit is as follows:- Capacitor Cl provides the integration for the internal conversion process of the integrated circuit. Capacitor C2 reduces noise and instability on the converter by ac decoupling a guard ring on the printed circuit board.

Crystal XTALl with its associated capacitors generate a 2.45MHz clock, to which the internal IC circuit is locked..

Diodes Dl, D2 and D3 together with R5 and C3 provide a reference voltage of approximately 1.5V. The stability of the reference is not critical as the voltage returned to the analog input is internally compared with reference and the result of the comparison is a digital number expressing the input as a proportion of the reference voltage i.e. Vref=255 (hex FF) 0V=0. Capacitor C4 removes transient noise from the power supply.

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Line resistors Rl, R2, R3 and R4 are purely protection devices to prevent high energy pulses damaging the input circuitry of the IC.

The input of the IC must be high impedance, greater than 10M ohm so that its effect on the keyboard effective resistance and series protection resistor is negligible.

The interface to the controlling device is via signals DO through D7 (the data bus) and the selection signals WE/, RD/, CS/, AO, & Al.

Only the relevant states used in this application are described. Other states such as 10 bit conversion have been suppressed.

Computer apparatus in accordance with the invention thus enables complex alphabetic, character, or word- based games to be played with the same facility that joy-stick controlled video games are currently played. However, games being developed for use with the invention not only assist in training hand-eye co-ordination (as do current games of the "Space Invaders" - trade mark type) but can and very preferably do have a high level of mentation. Players will have to think and construct quickly in words and numerals as well as being able to react quickly. In teaching applications, the practical usage of

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a single micro-computer, of which many already exist in schools and colleges, can be extended four or five-fold. Additionally, the "game" facility can be used to teach computer usage to children whilst capturing their attention and enthusiasm. Given a central computer of sufficient speed and capacity, a large enough video display, and a suitable A-D converter (i.e. faster and of high input impedance) there is no reason why a whole class room, of say 32 pupils, should not be simultaneously linked to the computer; each with a respective remote chord keyboard.