DESCRIPTION Field of the invention The present invention concerns a device and a process for the connection of electronic components, suitable for the simultaneous switching of communication links and of power supply to the same.

Background art Devices of the"Data switch"type are known, which allow for the sharing (not simultaneous) of two or more printers on the same PC or the sharing (not simultaneous) of two or more PCs on the same parallel printer. The switching can occur manually or electronically.

A first disadvantage of such devices is that of acting as a switch only on the data links and not on the power supply of the two printers or two PCs as well. A second disadvantage is due to the fact that these components have a limited number of communication links and of switchable components. Since in general these switches are used in communication interfaces that make use of parallel ports, a further disadvantage is that they only guarantee the quality of the signal passing through for frequencies of about 4 Mbps.

Moreover, devices of the"computer switch"type are known which enable the centralised control of a number of PCs which can vary from 2 to 6 by means of a keyboard, a mouse and a monitor. The switching of the PCs occurs by the keyboard or by manual switching, allowing the operator to work in environments which change from time to time.

A first disadvantage is due to the fact that these devices do not act in the switching of the power supply of the PCs, since these all remain switched on whichever PC is used. A second disadvantage of these devices is given by the fact that it is not possible to work on different environments residing on the same PC, but only on environments residing on different PCs. A further disadvantage is due to the fact that these devices can only work on a limited number of PCs.

In addition, devices of the"PC sharing"type are known, which are in fact a mirror version of the computer switches, in that a number of users (variable from 2 to 6) equipped with a keyboard, video and mouse can interact alternately with a single PC. During normal operation, a user who wants to work on this PC will have to request agreement for access from all the other users, or wait until access is free.

A first disadvantage is shown by the fact that there is no switching action on the power supply of the stations of the various users. A second disadvantage is due to the fact that these devices can only work with a limited number of users.

It is then possible to note how the switching devices of known design present the common problem of being unable to act on the power supply of the components which are switched.

Summary of the invention The present invention solves the aforementioned problems of the previous state of the art, in that it provides for, in a system composed of multiple components potentially communicating with each other, the connection of the preselected components and the functional and

electrical insulation from other system components. In particular, a device for connecting a group of electronic components and a user system equipped with a communication link to the outside, each of said components being equipped with a dedicated communication link to the outside and with a dedicated power supply link, characterised in that it comprises: -a first group of connection means, for connecting said device with the communication links and the power supply links of said group of electronic components; -a second group of connection means, for connecting said device with the communication link of said user system; and -means for selectively connecting a component of said group with said user system, comprising : -communication selection means, for selecting the connection between the dedicated communication link of said component and the communication link of said user system, the outside communication links of the components which are not selectively connected being not enabled; -power supply selection means, for connecting the power supply link of said component with a power supply, the power supply links of the components which are not selectively connected being not supplied; and -a control unit, for simultaneously controlling said communication selection means and said power supply selection means.

Furthermore, a process is provided for selectively connecting a component of a group of electronic components and a user system equipped with a communication link to the outside, each component of the said group being equipped with a dedicated communication link to the outside and with

a dedicated power supply link, characterised in that it comprises the following steps: a) selecting a connection between the dedicated communication link of said component and the communication link of said user system, the outside communication links of the components which are not selected being not enabled; and b) selecting a connection between the power supply link of said component and a power supply, the power supply links of the components which are not selectively connected being not supplied, in which steps a) and b) are carried out simultaneously.

It is to be noted that in the present description, the term"electronic component"will be understood to mean any device equipped with at least one communication link on which data and/or signal levels are transmitted.

Preferred features of the present invention are provided in the dependent claims.

A first advantage is due to the fact that the present invention proves itself to be particularly useful in all systems in which it is necessary to change over the communication links between the components of the system, for security needs, continuity of the service supplied or for production or control needs, with concomitant exclusion of the power supply of components which are not used. Such an exclusion of power supply is useful not only as far as energy saving is concerned, but also in order to avoid damaging overloads of the system itself, which can bring about interference and noise caused for example by a higher temperature stress to the components, such that the correct operation of the system is affected.

A second advantage is due to the fact that the device and the process according to the present invention act in the system in a totally transparent way, that is to say they do not interfere with the operation of the components but merely enable their connection and activation in the system.

A further advantage of the present invention is related to the fact that, by not using multiplexing devices (multiplexers), it does not require the corresponding demultiplexing devices (demultiplexers), nor does it require any type of decoding.

A further advantage is due to the selectivity of the communication, in that only the selected components are activated, without the possibility of interference or overlay with not selected components, in that their interfaces are disabled.

Yet a further advantage is due to the fact that the device and the process according to the invention require- for operation-no hardware or software reconfiguration by the user, and therefore they are suitable for use by staff who have no particular technical skills.

Yet another further advantage is due to the fact that, once used automatically, the device and the process according to the invention enable a change of component to be carried out in an extremely short time (in the order of milliseconds) and without the intervention of the operators. This proves to be particularly important in cases where systems with complex circuitry and operation require an immediate resetting ability, which even the intervention of the operator on site cannot guarantee.

Yet a further advantage is shown by the possibility of permitting the transit of bi-directional signals whose only

limitations are constituted by the frequency limitation of the connected components and not by the device according to the invention. It should also be appreciated that the number of communication channels concerned with the device is widely variable depending on the different uses from time to time.

A further advantageous characteristic of the present invention is the interchangeability between the user system which is upstream and the components which are downstream of the switching device. In fact, in certain configurations, there may be the possibility of obtaining for one of the downstream components the functionality of a user and at the same time for the user of obtaining the functionality of a component.

An advantageous embodiment of the present invention then provides for the possibility of disabling the switching control during normal operation of the system, so as to avoid sudden changes of configuration which lead to possible malfunctions due to accidental switching of the equipment without the necessary procedures or precautions required by the application.

A further advantageous embodiment then provides for, in case of a power failure, the successive automatic resetting of the connection typology present prior to the disruption.

In this way, the possibility is avoided that, after the resumption of power, the system assumes incorrect configurations which lead to anomalies or malfunctions of the system.

Various are the fields in which the device according to the present invention can be applied, such as industrial electronics, industrial automation, active security in civil (e. g. alarm installations) and industrial (e. g.

machinery and instrumentation) ambit, computer environments, networking environments, telephone (and via cable in general) communication environments.

The components which potentially communicate with each other and to which the device according to the present invention is intended to apply can be for example devices for end use, machinery, processors such as PCs, modems, telephone exchanges, active network equipment, PLC, alarm exchanges, security devices, printers, peripheral devices, video and many more, in other words any device of electronic type which permits the transmission and/or reception of data along one or more communication links.

In particular, the present invention proves to be especially suited for"mission-critical"type working environments, in which no interruption whatsoever is permitted to the service provided by the system, even in case of damage, breakdown or maintenance stops of the components of which it is composed. A"mission-critical" system is managed according to a"fault-tolerance" criterion: the system's critical equipment is therefore doubled, tripled or at any rate increased in number with identical backup equipment. The system therefore ends up composed overall of a series of redundant equipment that must come into use in case of damage, breakdown or due to programmed or extraordinary maintenance of the critical equipment.

Below are some application examples in systems of the fault-tolerance type.

1) A system for the measurement and/or control of power plants. The device according to the invention is arranged between a group of components for detecting events (such as probes, thermometers, status levels, pressure or flow rate

measuring units, amperometers, voltmeters etc) and a control instrument. As soon as this control instrument suffers a breakdown, the device according to the invention performs the switching to a backup control instrument.

2) A system for the adjustment, command and control, mounted for example on a car or an aeroplane. The device according to the invention is arranged between a component for monitoring events (speed, engine rpm, ABS signals etc.) and a controller. As soon as this controller suffers a breakdown, the device according to the invention performs the switching to a backup controller.

3) An anti-intrusion system with multi-safety installations. The device according to the invention is arranged between a monitoring component (alarm sensor) and an alarm controller. As soon as this controller suffers a breakdown, the device according to the invention performs the switching to a backup controller.

4) Critical nodes for data transmission networks. The device according to the invention is arranged between a user system and an active network component (for example a hub, a switch or a router). As soon as the active component suffers a breakdown, the device according to the invention performs the switching to a backup component.

5) A PLC for the automatic management of production on machine tools. The device according to the invention is arranged between a machine (electrovalve, end stop, emergency button, motor, axles etc.) and a PLC. As soon as the PLC suffers a breakdown, the device performs the switching to a backup PLC.

6) A telephone system with several exchanges. The device according to the invention is arranged between the telephone users and a telephone exchange. As soon as the

exchange suffers a breakdown, the device performs the switching to a backup exchange.

7) A PC which manages or supervises an automatic process. The device according to the invention is arranged between a component suitable for carrying out an automatic process and a PC. As soon as the PC suffers a breakdown the device performs the switching to a backup PC.

8) An electro-medical control system for an intensive care hospital department. The device according to the invention is arranged between a group of equipment monitoring the state of the patient (sensor, electrode, converter etc.) and electro-medical equipment. As soon as the electro-medical equipment suffers a breakdown, the device performs the switching to backup electro-medical equipment.

Below are some examples of applications in production, service and security systems.

1) The selection of the modem to be used by the user.

The device according to the invention is arranged between a processor, for example a PC, and a system composed of an analog modem and an ISDN modem or, more generally, modems each operating according to different protocols. As soon as it is required, the device according to the invention performs the switching from the analog modem to the ISDN modem.

2) The selection of the processing system, for example a PC, and the telephone link to be used. The device according to the invention is arranged between a modem and a system composed of numerous processors. As soon as it is required, the device according to the invention performs the switching from one processing system to another and the switching of the relative telephone link.

3) The selection of the machine to be working. The device according to the invention is arranged between a PLC (for example) and a system composed of numerous machines.

As soon as it is required, the device according to the invention performs the switching from one machine to the other.

4) The selection of the processor, for example a PC, to be connected to the data transmission network. The device according to the invention is arranged between a data transmission network and a system composed of numerous PCs.

As soon as it is required, the device according to the invention performs the switching from one PC to the other, and therefore the access of a single PC to the data transmission link.

5) The selection of the operating system and of the working software platform on a single processor, for example a PC. The device according to the invention is arranged between the motherboard of a PC and a system composed of numerous peripheral devices, each potentially containing a different operating system and a specific software platform. As soon as it is required, the device according to the invention performs the switching from one platform to the other.

6) The conditional access of a processor, for example a PC, to a database. The device according to the invention is arranged between a database and a system composed of numerous PCs. As soon as it is required, the device according to the invention performs the switching from one PC to the other and thus the access to the database of the selected PC.

7) The conditional access of a user to a dedicated communication link connected to a specified component or

group of components. As soon as it is required, the device according to the invention performs the connection of a user to the dedicated link.

8) The selection of miscellaneous equipment. The device according to the invention is arranged between a group of miscellaneous equipment (printer, modem, DVD readers, machines, measuring instruments etc) and a PC. As soon as it is required, the device according to the invention performs the connection of one of these pieces of equipment to the PC.

9) The selection of monitors for specific applications, such as airports, control centres, stations etc. The device according to the invention is arranged between a group of monitors and a control or video recording set. As soon as it is required, the device according to the invention performs the connection of one of these monitors to the control and/or video recording set.

Brief description of the drawings The present invention will now be described hereafter with reference to its embodiments illustrated by way of example in a non-limiting manner.

In a first embodiment, reference will be made to the selection on the same PC of the operating system and of the working software platform which is resident on it.

Nevertheless, it is to be appreciated that operating systems suitable for operation on numerous software platforms are also to be envisaged. Such applications are particularly interesting for the purpose of limiting the phenomena of external intrusion into the system by unauthorised users and circumventing possible damage brought about by viral contamination of the system.

Reference will be made to the figures in the attached drawings in which: Figure 1 shows a basic diagram, suitable for illustrating the operation of the device according to the present invention; Figure 2 shows a more detailed block diagram of the device according to the invention; Figure 3 shows a diagrammatic representation of a device for checking the component switchover; Figures 4 and 5 show electrical diagrams suitable for representing in detail the block diagram in figure 2; and Figure 6 shows a diagrammatic representation of a second embodiment of the device according to the invention.

Description of a preferred embodiment of the invention The embodiment explained with reference to figures 1 to 5 refers to an application which is concerned with the switchover of two hard disks installed on a motherboard with databus in standard IDE. What illustrated by the description which follows concerning the switchover of two components, will make it possible to understand the way in which the connection device according to the present invention is able to switch a virtually unlimited number of external peripherals and links-which can operate with different protocols-constituting the databus.

With reference to figure 1, a user system represented by a motherboard 1 of a processor contains a CPU 2 connected to a databus 3 by means of a connection 4. The data which are present on the databus 3 is connected by means of a connector 5 to a bus interface cable 6, the latter being used to connect the motherboard 1 with the device according to the present invention, indicated in its entirety at 7.

The device 7 includes means for selectively connecting an electronic component, represented in the figure by means of a circuitry 29 for the switchover of communication links and a circuitry 30 for the switchover of power supply links. In particular, the circuitry 29 includes a switch 8 for the communication links of peripheral devices, while the circuitry 30 includes a switch 9 for the power supply links of peripheral devices. These switches are suitable for being actuated simultaneously by a command coming from a control unit 50, which will be described in greater detail in the following figure 2.

The switch 8 for the communication links of peripheral devices is one which enables the switching of data coming from the motherboard 1 (or entering the motherboard 1) between two electronic components, namely a first hard disk 10 (hard disk A) and a second hard disk 11 (hard disk B).

Thus, the connection is selected between a dedicated communication link 13 of hard disk A or a dedicated communication link 17 of hard disk B and the interface cable 6, the latter acting as the dedicated communication link of the system constituted by the motherboard 1. The switch for the power supply links of external peripherals 9 is one which enables the switching of the power supply coming from a power supply block 12 between the hard disk A and the hard disk B.

Thus, the connection is selected between a input power supply link 14 to the hard disk A or a input power supply link 18 to the hard disk B and the power supply block 12.

The interface 13 and power supply 14 cables coming out of hard disk A are connected to the connections 15 and 16 respectively of the device 7. The interface 17 and power

supply 18 cables coming out of hard disk B are connected to the connections 19 and 20 respectively of the device 7.

It will be easily appreciated that the simultaneous actuation of the peripheral device switch 8 and the power supply switch 9 will be such that it causes neither the data link nor the power supply to hard disk A during the operation of hard disk B and vice versa. It can therefore be seen how, by means of the device according to the invention, the communication links to the outside of not selectively connected components are not enabled.

The following figure 2 shows in greater detail a diagram of the device according to the invention, in particular with reference to the control and power supply unit 50, suitable for the simultaneous control of the communication selection means and the power supply selection means.

With reference to such figure, a general switch 21 is connected to a power supply group 51 by means of a connection 22. The switch 21 is preferably a multi-pole switch, in which a first series of contacts provides for the omnipolar sectioning of the power supply voltage (as per legal and safety standards), while a second series of contacts provides for-in the case at issue-the setting to zero of a memory, as described below.

In the depicted embodiment, the power supply group 51 includes a +5V direct voltage power supply unit 23 and a +12V direct voltage power supply unit 24. In particular, the power supply unit 23 supplies various components both inside the unit 50 and to the remaining parts of the device 7, in particular the circuitry 29 for the switchover of the communication interfaces. The power supply unit 24 instead

supplies the circuitry 30 for the switchover of the equipment's power supplies.

Indicated at the numeral 25 in the figure, there is a component switch. This switch can operate in three different modes: a) Manual. In this case the switch 25 has a number of positions equal to the number of switchable components.

In order to avoid, during normal operation of the system, unexpected and unforeseen changeovers of component due to inexperienced or accidental manual movement of the switch, the manual mode advantageously provides for-with the aim of a greater safety-the changeover of peripheral devices being made effective by carrying out, apart from the change of the position of the switch, an additional second operation which varies for each application.

Therefore, means are provided for preventing a further switching following the execution of a first switching. In the embodiment at issue, the changeover of peripheral devices on a PC is such that the actuation of the general switch is made necessary in order to carry out a new component switching. b) Automatic. This mode is particularly efficient in all systems where, in case of a breakdown of a piece of equipment, its substitution is required-by means of switching on to another piece of equipment-in an extremely short time and without operator intervention. c) Remote. A mode such as this is similar to automatic mode and permits the acceptance of the external signal from a remote station.

The switch 25 is supplied by means of the +5V power supply unit 23. The signal relevant to the type of switching which is desired to be carried out, coming from

switch 25, is first sent to a device 26 for memorising the selected component. The device 26 is such that it acts as a memorisation means for the selected component and includes a number of memory cells (suitable for example for assuming a HIGH value or a LOW value) in order to memorise the status of each component. For example, the HIGH status will be used to indicate that the piece of equipment is selected or in use, while the LOW status will be used to indicate that the piece of equipment is not selected or not in use.

As one single component in particular is activated at a time, only one memory cell will assume the HIGH status, while the others will assume the LOW status.

The memorising of information relating to which piece of equipment is in use is particularly useful in case of power failures, in that this information can be conveniently memorised even in the absence of power voltage for a certain time. When power supply is resumed after a black-out, the device will automatically be able to switch back onto the piece of equipment in use, in that it will check which of the memory cells of device 26 is set to a HIGH value.

Advantageously, a unit 27 for setting the memory to zero is connected to the device 26. The unit 27 acts as a means for reinstating the initial status of the memory device 26. By means of this unit it will be possible- whenever it may be necessary-to return all the memory cells of device 26 to a LOW value, in order to avoid possible malfunctions or errors of activation of the component. Both the device 26 and the unit 27 are supplied by the +5V power supply unit 23. In case of the aforementioned automatic switching, the switch 25 will be equipped with an electronic circuit which at its input

recognises an external signal, on the basis of which it sets the memory device 26 to zero by means of the unit 27, memorises, in the memory zone relative to the preselected component, the status of this component and then switches the system automatically to one of the backup pieces of equipment.

The memorisation device 26 is connected to a unit 28 for changing over the component and displaying the component in use. The unit 28 acts on the basis of the status of the memory cells of device 26, in that it is activated by means for example of the HIGH status of one of these. Preferably, the device according to the present invention is such to provide for a variety of signalling LEDs, a single one of which is lit up at a time, namely that which pertains to the piece of equipment in use at that moment. In the event of a power failure, on the resumption of electric power the LED lighting up will be advantageous, in that it will enable the indication of which component was operating at the moment of disruption.

These LEDs thus act as means of visual identification of the component the communication link of which is connected with the communication link of the user unit.

Now, reference will be made to the changeover circuitry 29 and 30. Each one of these can have, as shown by way of example in the figure, a variety of connectors. In particular, the circuitry for the changeover of the communication links 29 has a connector 52 for the connection to the motherboard, a connector 53 for the connection to the hard disk A and a connector 54 for the connection to the hard disk B. Conversely, the circuitry for the changeover of the power supply links has a connector 55 for the connection to the power supply 12, a

connector 56 for the connection to the power supply of hard disk A and a connector 57 for the connection to the power supply of hard disk B.

The circuitry 30 for the changeover of the power supply links provides for the switching of the power supply coming from the power supply group 12 on the power supply connector of the preselected component. The power supply switching can for example take place by means of a relay with double changeover contacts (5A, 250 V per contact, in which the power supply voltage of the coil is +12V).

The circuitry for the changeover of the communication links 29 provides for the switching of the communication links coming from the motherboard 1 on the communication connector of the preselected component. The unselected components do not provide for any passing of signals along their communication links. The switching of the network interface cables takes place for example by means of integrated circuits of the SN74CBT16210 type from Texas Instruments.

Depending on the user application, the signals may be of mono-directional or bi-directional type and it may obviously provided for different signals depending on the values of the amplitudes of voltage and current, the type of signal and the signal frequency. The electronic systems which manage the circuitry for the changeover of the communication links will be set according to technical specifications which differ from time to time. Therefore, it is possible to provide for a great variability, due to the number of channels, the physical typology of the channel (UTP cable, parallel cable, telephone cable, parallel tracks on a card, etc), the electrical characteristics of the transmitted signal (directionality,

frequency, wave shape, voltage levels etc), or again to the electrical homogeneity or heterogeneity of the signals travelling in the interface. With reference to the latter case, there may be for example cases in which the communication interface is made up of multiple interfaces which are heterogeneous with respect to one another: telephone signals, data transmission networks, analog control signals of probes etc.

For example, in the case at issue, the communication interface is constituted by a databus in standard IDE.

Obviously, different standards can be considered, such as the SCSI standard, which provides for a different number of communication channels.

An advantageous characteristic of the device according to the invention is the one provided for in figure 3, namely a device 31 for checking the equipment changeover, i. e. checking that the selection has occurred, arranged downstream of the changeover circuitry 29 and 30. This device can for example be realised by means of a logic unit which changes its own status once the switching has taken place successfully. The signal relative to the status of the checking device 31, as an output thereof, can be used as data for checking the operation of the system, for example in remote switching of components by possible remote controls on the network node or visual signalling on synoptic panels.

Referring back to the embodiment in figure 2, an electric diagram shown in figures 4 and 5 by way of example of the device according to the invention, will be described hereinafter. With reference to figure 4, the activation of the device according to the present invention by means of the switch 21 supplies a +5V voltage on the contact of a

manual peripheral device selector 101 identifying the component switch 25. This selector 101 is represented in the figure in its position of selection of hard disk B. In this way, the selector 101 enables the power supply of the +5V voltage on the collector of transistor Q1. The activation by means of switch 21 will also ensure the discharge of the capacitors Cl and C2 arranged on the top left in figure 5 and which are part of the memorisation device 26 of the selected component. In particular, each of the capacitors Cl and C2 acts as a memory cell suitable for memorising the status of the piece of equipment to which it refers.

The circuit in the figure is such that it includes a couple of inverters INV1, INV2 on the inputs of which resistances R7 and R8 are arranged. Since resistances R7 and R8 are respectively connected to earth, on the inputs of the inverters INV1 and INV2 (for example of the 74LS14 type) there will be a LOW logic level. As a result, on the outputs of the inverters INV1 and INV2 there will be a HIGH logic level. This logic status will be brought back onto the bases of the transistors Q1 and Q2 through the resistances R12 and R13.

At this point, the transistor Ql will end up under conduction and-by means of the resistance Rl positioned on its own emitter-will start charging the capacitor Cl.

The transistor Q3, positioned parallel to the capacitor C1, will be blocked, in that its base will not be polarised.

The transistor Q2 will also remain blocked since, although having a polarised base (HIGH output of INV1), its own collector is not connected to the power supply.

The provision of the transistors Q3 and Q4 is advantageous, in that it allows the capacitors Cl and C2 to

be discharged by means of an external impulse applied to the pin of the connector 102, when necessary. The connector 102, the transistors Q3 and Q4 and their resistances of polarisation thus constitute an embodiment of the unit 27 for resetting to zero of the memory, described with reference to the previous figure 2.

In case of a possible loss of mains voltage, when power is restored the device according to the present invention will automatically be restored on the peripheral device relative to the HIGH logic status maintained on one of the two capacitors Cl or C2. This therefore ensures the automatic restoring of the system on the hard disk in use, as soon as the electric power returns.

As a consequence of the HIGH logic status of C1, a Darlington stage formed by the transistors Q5 and Q6 is polarised through the resistance R5. The input of the inverter INV1 becomes HIGH, and its output attains a LOW logic status. On the base of the transistor Q2, connected to the output of the inverter INV1 by means of the resistance R13, a LOW logic value will be established. The presence of this LOW value is such that the transistor Q2 is maintained in a blocked state even should the manual switching of the peripheral device inadvertently shift from its appropriate position selecting hard disk B to the position for selection of hard disk A. In this way, an advantageous embodiment of the above described blocking means is therefore obtained, such that possible accidental movements of the manual switch, possibly causing damage to the system due to the contextual modification of the component selected, are prevented. A Darlington stage at the input to INV1 and INV2, is chosen, in the circuit in the figure, for having a value of b equal to 50,000. In

view of the fact that the resistance R7 on the emitter of the transistor Q6 is equal to 3.3 kW, a very high impedance (in the order of 1650 MW) will be obtained on the base of the transistor Q5, so as to prevent the capacitor Cl from discharging in normal operating conditions of the circuit.

The provision of the Darlington stage also permits to maintain the charge of Cl for a period of about 48 hours in case of power failure. The maintaining of the charge of Cl will permit-when the power supply returns-the enabling of the peripheral device in use (hard disk B in the case at issue) at the time of the energy disruption.

The outputs of the inverters INV1 and INV2 are respectively connected to the inputs of the inverters INV4 and INV3, which for example may be of the 74LS14 type as well. The output of the inverter INV4 will be in a HIGH logic status, so as to polarise the transistor Q31 and will enable the consequent switching on of the LED D11 relative to the status of use of hard disk B. In the opposite case- hard disk A operating-the transistor Q30 will be the one to be polarised and therefore the LED D10 the one to be switched on. The LEDs D10 and D11 therefore constitute the means for displaying the component in use, described with reference to the unit 28 in figure 2. Furthermore, the outputs of the inverters INV1 (LOW) and INV2 (HIGH) are such that they provide the logic levels to the pins 1 and 2 of the connector 103, connected to the connector 104 in the successive figure 5.

With reference now to this figure 5, the logic levels exiting from connector 104-in the case at issue +5V on pin 5,0V on pin 2,0V on pins 1 and 3 and +5V on pin 2- permit the simultaneous enabling of the integrated circuits 63 and 64, assigned to the communication of the hard disk B

on the databus, and the blocking of the integrated circuits 61 and 62, assigned instead to the communication of the hard disk A on the databus. The integrated circuits 61,62, 63 and 64 can be for example of the SN74CBT16210 type.

Returning again to the description of figure 4, it is to be noted that the output of the inverter INV1 (LOW) is brought back on to the base of a Darlington stage consisting of the transistors Q50 and Q51, which can be seen at the bottom left of the figure. The coil of a relay REL2 is arranged on the collector of the transistor Q51, said coil enabling the switching between the power supply to the hard disk A and the power supply to the hard disk B.

In this respect, it is to be noted that the connectors 106 and 107 function respectively by connectors for the power supply to hard disk A and to hard disk B. These connectors receive as an input, depending on the status of the relay REL2, the voltages coming from the connector 105 and then supply them to the hard disks A and B.

The outputs from the inverters INV1 and INV2 are also connected to the inputs of a port XOR 104 (for example carried out by means of the MC14070 equipment) downstream of which a Darlington stage is arranged, constituted by the transistors Q52 and Q53, responsible for turning the computer on (ON PC), by the triggering of the relay REL1.

It can therefore be noted how in this example the changeover of the peripheral device precedes the switching on of the PC. This means that once the PC is started up, it automatically sets itself to the switched over peripheral device, thus avoiding conflicts with particular processes or operations which may bring about damage or anomalies to the system.

The provision of the port XOR 104 is advantageous, in that it allows the prevention of any circuit logic inconsistencies, in the case where the same logic level occurs as an output from the inverters INV1 and INV2, instead of complementary logic levels as it should be. The output from the port XOR 104 has a HIGH logic level only in the case where the two inputs A and B have complementary values, and therefore only in case of a correct operation of the device. This port XOR could for example be an embodiment of the device 31 for checking the component changeover.

As already mentioned with reference to previous figure 2, the device according to the present invention is equipped with its own power supply group 51, including a +5V power supply unit 23 and a +12V power supply unit 24.

The power supply unit 24 is carried out in the depicted example by means of a MC7812ACT type integrated circuit.

The regulated voltage of +12V is used to supply the coils of the relays REL1 and REL2. The regulated voltage of +5V of the power supply unit 23 is used instead to supply all the remaining componentry of the circuit.

An advantageous feature of the embodiment here described is given by the possibility of providing for a stage which enables-with PC switched on and therefore following to the excitation of the coil REL1-the blocking of the +5V voltage coming from the regulated power supply unit 23 and substituting this with the +5V voltage coming from the PC.

It is in fact to be noted how, as the device according to the invention is started, the transistor Q120 is blocked, the relevant base being earthed by means of the resistance R102. The blocked condition of the transistor

Q120 is such that it enables the conduction of the transistors Q110 and Q95, which in turn permit the power supply of transistor Q85. A 6.2 V Zener D18 diode is arranged on the base of the transistor Q85, and is supplied by means of the resistance R60 positioned between its cathode and the emitter of the transistor Q95. Therefore, on the emitter of the transistor Q85 there is a 5.6 V voltage. The value of +5V of the output voltage of the regulated power supply 23 is then obtained thanks to a diode D80, which enables the drop in voltage from 5.6V to 5V. With the aim of protecting against any surcharges and overloads, the power supply unit 23 is equipped with a 200 mA fuse F and a Zener DZ 6.2 V diode.

Once the PC is started up, there will be a +5V voltage on the pin of connector 105; this voltage will be supplied onto the base of the transistor Q120 by means of a resistance R103. The transistor Q120 will therefore be in conduction, and consequently the transistors Q110 and Q95 will be cut off. Therefore, the power supply stage regulated at +5V formed by the Zener D18 diode and the transistor Q85 will be excluded. However, the +5V voltage will be supplied to the entire device by means of the diode D15, which is also supplied, like the transistor Q120, by the +5V voltage coming from the PC by means of the pin 1 of the connector 105. Thus, the +5V power supply voltage will be by-passed through the above described substitution means of the power supply coming from the power supply unit 23.

The +5V voltage will therefore be supplied to the device from the PCs power supply. Concluding this part of the description which has been made with reference to figure 4, it has to be added that the initial actuation of the general switch 21 also enables the actuation of an impulse

by the connector 102, such as to discharge the capacitors C1 and C2 and thus reset to zero the contents of the memorisation device 26.

The description given here refers to an application where standard logic levels (HIGH = +5V, LOW = 0V) are necessary. Therefore, with the aim of achieving a greater reliability, the electronic systems used are mostly constituted of discrete equipment and TTL, while the integrated circuits are constituted by CMOS. However, it is possible to envisage, by using various different interfaces, equipment carried out according to the most different typologies, both for operation and characteristics and for the exchange of data of a more complex and numerous type.

It is furthermore to be understood that the above detailed examples have been applied to the changeover of two single components for the sake of clarity.

Nevertheless, the number of components can vary according to the requirements which differ from case to case. It may also be possible to have an auto-power supply of the implemented circuitry.

The following is a description of an alternative method of application of the device according to the present invention. This application refers to computer networks of the mission critical type, whose priority is that of absolutely guaranteeing full time service. These computer networks are present for example in airports, banks, insurance, stock exchanges, exchange companies, brokerage exchanges, providers etc. The critical point of these computer networks is represented by the active components which make up the neutral point, such as the hub, switch, bridge, router, gateway etc. In these components any

damage, breakdown or simple stops due to normal maintenance can place the entire system seriously in crisis, bringing about enormous economic damage.

By means of duplicating the critical active components of the computer node it is possible to obtain a fault- tolerance system, and therefore a system which offers greater guarantees for continuous full time supply of the network service. The application of the device according to the present invention described herein enables the utilisation of the fault-tolerance policy, permitting the utilisation of backup components and blocking the damaged component, thus avoiding any intervention of the operator on site. The changeover mode also in this case can be either manual (in case of ordinary or extra-ordinary maintenance) or automatic or remote (for example in case of damage to the component).

A conceptual scheme of this application is shown in Figure 6. In this figure, a user system can be seen constituted of a group of n users 40, connected-by means of the device 7 according to the invention-to an active network component 41, such as a hub, a switch type unit or a router. The device according to the present invention is such that n ports are provided, both on the input connector 42 and on each of the two output connectors 43,44.

The component 41 contains a connection and routing grid 45 typical of the operation of the component itself, and a power supply unit 46. As soon as this component 41 breaks down, this will send a fault signal along the connection 47, signal which will be collected and interpreted by the control unit 50, which will control the switching inside the changeover circuitry 29 and 30. At this point, the

users 40 will be connected to the backup active component 48.

In any case, it can be seen how, in spite of the variety of the applications, the principles applied are substantially identical to those explained in the first embodiment.

The present invention has been described herein according to its embodiments presented by way of example and in a non-limiting manner. It is to be understood that there may be other forms envisaged, all to be considered as falling within its scope of protection.