GB2234378A - Keyboard for a public terminal - Google Patents

Abstract

A keyboard comprises an assembly of keys T coupled to a microcontroller 10 by means of m conductors (L1 - L8), connected to m ports (P1-P8) of the microprocessor (10) for the sequential scanning of the keyboard. Each key has n contacts connected to a respective combination of n of the conductors. n may be 2 or 3. <IMAGE>

Description

KEYBOARD FOR A PUBLIC TERMINAL The present invention concerns terminal keyboards and in particular terminal keyboards for wide distribution having a relatively small number of keys in comparison with the number of keys on keyboards for professional equipment.

Terminals for the general public, for example videotext terminals such as those known under the name Minitel, have a keyboard with a number of keys which is in general from 60 to 80. In comparison, keyboards for prdfessional equipment are mostly keyboards with more than 100 keys. In these two types of equipment, a microcontroller ensures in particular the scanning of the keyboard. The size of the microcontroller is chosen according to the type of equipment involved and depends upon the functions which are assigned to it.

In public terminals, the size of the microcontroller also takes into account the objective of an overall cost which is as low as possible.

Whatever the type of equipment under consideration, the function of scanning the state of the keyboard is a function which is demanding in the number of microcontroller ports assigned to it. In public terminals, this scanning function limits other possible functions and prevents their optimisation.

Currently, the structure of keyboards for their scanning is of the matrix type: it uses a multiplexing in p lines and q columns of connections between the keys and the microcontroller, for a keyboard of p x q keys. Each of these keys has two contacts, one connected to a line and the other to a column. To this matrix are assigned p + q microcontroller ports which form p outputs corresponding to p lines and q inputs corresponding to q columns.

Each key corresponds to the selection of one of the inputs and one of the outputs, the corresponding line and column of which, in the matrix, are connected to each other when the key is depressed. Scanning of the keyboard thus takes place in sequential manner by the selection of the different outputs, one after another, and by the detection of the states of the inputs for each output selected.

For this keyboard scanning, the q inputs are connected to individual return resistances, and the p outputs are insulated from each other by diodes, each of which is associated with each key and is mounted between each line and each column with the key concerned, or they are mounted in an open collector.

The matrix-type structure with diodes is produced on a support in a printed circuit; the matrix-type structure without diodes is produced on a flexible support such as that known under the trademark "Mylar".

From the document US-A-4 609 792 a keyboard is also known, the different keys of which each have two contacts with which there is associated an additional earth contact. The two contacts of each key are connected to two of the conductors of an assembly of conductors. The different two-by-two combinations of these conductors correspond at least tithe different keys. The additional earth contact of each of the keys is connected to a common earth line. The assembly of the conductors and the common line is brought back to a terminal connection which enables the pressed or unpressed state of the different keys of the keyboard to be read directly.

An object of the present. invention is, for the scanning of a public terminal keyboard by a microcontroller, to reduce the number of microcontroller ports which are assigned to this function, without excessively increasing the number of contacts of the individual keys of the keyboard.

According to the present invention there is provided keyboard for a terminal, comprising an assembly of simple keys, each of the said keys having n contacts but having no common earth contact for the keys, the keys being coupled to a single network of conductors for the scanning of this keyboard by means of a microcontroller, the single coupling network having a limited number m of conductors, different combinations of which in groups of n correspond To different keys of the said assembly, each key being connected to the n conductors of the combination for the key under consideration, and the m conductors of the said network being themselves directly connectable to m individual input/output ports of the said microcontroller, making the said network twodirectional.

According to another feature, the keyboard further comprises a microcontroller unit, and the said ports of the microcontroller unit are connected to an internal microcontroller defining, for each of the m conductors of the network, an output mounted in an open collector and an associated return resistance input (El).

In particular, each of the simple keys of the said assembly has 2 or 3 contacts for the conductors of the corresponding combination, with the different combinations of the m conductors defined in two-by-two or three-by-three correspondence. That is, the conductors are grouped in twos when each key has two contacts, or in threes when each key has three contacts, and each group is associated with a respective one of the keys.

The features and advantages of the present invention will emerge from the description of the exemplary embodiments shown in the attached drawing.

Figure 1 is a diagram of a keyboard with keys with two contacts according to the invention.

Figure 2 is a diagram of another exemplary embodiment of a keyboard with keys with three contacts according to the invention.

In these Figures, the same reference numbers have been used to denote identical or comparable elements.

Figure 1 corresponds to a keyboard comprising twenty-eight keys T and a network R of eight conductors L1 to L8 which couple the keys T to a microcontroller 10 for scanning the keyboard. Figure 2 corresponds to a keyboard comprising twenty keys T and a further network R of six conductors L1 to L6 which couple the keys T to the microcontroller.

In these two examples, the keys T are keys known as simple keys, for which one key at a time is depressed and is detected, and not function keys, for which the simultaneous depression of several keys is valid and corresponds to a function.

In Figure 1, it is the different possible two-bytwo combinations of the eight conductors L1 to L8 which give the number of keys of the keyboard; each of these combinations corresponds to a different one of the keys of the keyboard. Each key thus comprises, for the two of the eight conductors of the combination concerned for the key under consideration, two contacts connected respectively to these two conductors. These two contacts are denoted by the letter a, accompanied in each case by the reference numeral which is associated with the letter L of the conductor to which the contact is connected, that is to say, each of these contacts is denoted by one of the references al to a8.

On the other hand, in Figure 2, it is the different three-by-three combinations of the six conductors L1 to L6 of the network R which give the number of keys on the resulting keyboard. These different combinations of the conductors of the network also correspond to the different keys of the keyboard.

Each of the keyboard keys then comprises three contacts, each of which is connected to one of the three conductors of the combination which corresponds to the key under consideration. These three contacts are likewise denoted by the letter a, accompanied by the reference number associated with the letter L of the conductor connected to each of them, that is to say, by the reference al to a6, whichever is the case.

Only some of these references for the keys and their contacts are shown in the Figures, for reasons of simplicity. The number of keys chosen to be shown in the examples has also been limited for the sake of clarity in the Figures.

The conductors L1 to L8, or L1 to L6, of the network R for coupling the keys to the microcontroller, are connected to individual ports P1 to P8, or P1 to P6, of the microcontroller 10 for scanning the keyboard. These ports P are inputs/outputs for the conductors, which are not differentiated, in an assembly of lines and an assembly of columns of a matrix-type structure, which form between them a single network.

A circuit 11 inside the microcontroller enables the keyboard to be scanned. It connects each of the ports P of the microcontroller 10 to a corresponding input E and to a corresponding output S, shown solely in Figure 1 for the single port P1. This circuit 11 ensures the internal connection of the port P1 to the output S1 connected to the open collector of a transistor 12, and to an input El with which there is associated a return resistance 13 set at a positive reference voltage marked +.

Scanning of the keyboard of Figures 1 and 2 takes place in sequential manner for the said keyboards without an earthing wire. It is carried out by scanning the 0 volt at the successive individual outputs, whereas the other outputs are blocked, and by reading the states of the inputs with the passage of each one of the different outputs to the 0 volt, as with the known keyboards of matrix-type structure.

It is to be noted in respect of the assembly of keys T, all of which are simple keys, that a multiple depression of several keys does not permit detection of the simultaneously depressed keys, instead it permits detection of the multiple depression itself, and therefore of an erroneous corresponding instruction, which is not carried out but is signalled.

Of course, the keyboard having a single network of conductors and associated with the assembly of simple keyboard keys for the keyboard scanning, can be adapted for each particular piece of equipment in which it is used. Thus, generally, the keyboard has a single network of m conductors, the different n-to-n combinations of which define between them the number of identical simple keys on the keyboard. This number n is in practice limited to the value 2 or 3 for easy production of the keys, each with n contacts. The number n will be in any case less than or equal to m/2.

Such a structure of a keyboard having a single network of conductors for keyboard scanning has the essential advantage of reducing the number of microcontroller ports assigned to this function, without however necessitating too large a number of contacts per key.

There can thus be obtained, by way of example, a keyboard with 66 simple keys, each having 2 contacts, with a network of.12 conductors to which there are assigned 12 microcontroller ports, or a keyboard with 84 simple keys, each having 3 contacts, with a network of 9 contacts to which there are assigned only 9 microcontroller ports.

In comparison, a keyboard of matrix-type structure, having an approximately equivalent number of keys, uses a matrix of 8 columns and 8 lines, with 16 ports assigned thereto on the microcontroller, for a keyboard of 64 keys, or a matrix of 8 columns and 9 lines, with 17 ports assigned thereto on the microcontroller, for a keyboard of 72 keys.

Of course, a keyboard with a single network of conductors for an assembly of simple keys can further comprise several function keys. Such function keys are in practice very limited in number; generally, they are 2 or 3 in number and scarcely more. In this case, the keyboard comprises as many additional conductors as the desired number of function keys, that is to-say, 2 or 3 additional conductors, and these are similar to those of the network but do not belong to it, and each of them-is assigned to a function key and is connected to a microcontroller port. These function keys then have a simple contact for their own conductor. Such function keys are not represented in the examples shown.

In a keyboard according to the invention, comprising function keys, the gain in numbers of microcontroller ports is less sizeable than in a keyboard without function keys; this number of accesses, however, remains less than the number of microcontroller accesses for a keyboard with matrixtype structure having a comparable number of keys.

The present invention has been described in respect of the examples shown; to these, of course, can be added modifications without, however, exceeding the scope of the invention. It can be noted in general that, if maximum limitation of the number of conductors in the network is desired, the number of contacts of the simple keys must be increased. In practice, for reasons of feasibility and cost, simple keys with 2 contacts or 3 contacts are adopted.

Claims (3)

1. Keyboard for a terminal, comprising an assembly of simple keys, each of the said keys having n contacts but having no common earth contact for the keys, the keys being coupled to a single network of conductors for the scanning of this keyboard by means of a microcontroller, the single coupling network having a limited number m of conductors, different combinations of which in groups of n correspond to different keys of the said assembly, each key being connected to the n conductors of the combination for the key under consideration, and the m conductors of the said network being themselves directly connectable to m individual input/output ports of the said microcontroller, making the said network twodirectional.

2. Keyboard according to claim 1, further comprising a microcontroller unit, the ports of the microcontroller unit being connected to an internal microcontroller defining, for each of the m conductors of the network, an output connected to an open collector and an input with an associated return resistance.

3. A keyboard substantially as herein described with reference to, and as shown in, Figure 1 or Figure 2 of the accompanying drawings.