GB1588626A - Switching means - Google Patents

Description

(54) IMPROVEMENTS IN OR RELATING TO SWITCHING MEANS (71) We, ROLLS-ROYCE LIMITED, a British Company of 65 Buckingham Gate, London SW1E 6AT, formerly Rolls-Royce (1971) of Norfolk House, St James's Square, London SW1Y 4JR, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to switching means.

Computers produce an output signal which is fed to a display unit for the signal and which may be remotely located.

These display units cannot normally be disconnected from the computer when operational without overloading the circuitry of the computer or sometimes permanently damaging it.

It is an object of the present invention therefore to provide switching means which will enable a display unit for an output signal from a computer to be disconnected therefrom without affecting the performance of the computer.

According to the present invention switching means connected between a computer and a display unit between which electrical signals pass, comprise a conducting member for the signals and an impedance circuit, the impedance circuit being connected to receive the signals immediately before the conducting member ceases to conduct the signals and vice versa.

The impedance value of the impedance circuit may be at least as great as that of the display unit but is preferably substantially the same.

According to a preferred embodiment of the invention, the switching means comprises a plurality of conducting members and a plurality of impedance circuits, the switching means being arranged to pass electrical signals between a plurality of computers and at least one display unit, the conducting members being arranged to conduct electrical signals between at least one computer and a similar number of display units whilst the impedance circuits are connected to receive output signals from the remaining computers.

Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 is a schematic diagram of switching means constructed in accordance with the invention and arranged to switch any one of six computers to a visual display unit, Figure 2 is a schematic diagram of an alternative arrangement to that shown in Figure 1, and Figure 3 is a schematic diagram of the switching means with a visual display unit and a printer.

Computers supply output signals to one or more display units which may be remotely located. These display units may be many miles away from the computer, for instance, a computer in London could have display units in Birmingham and Glasgow.

The computers and the display units (VDU's) are physically connected by cables, and to disconnect a VDU from the computer whilst the computer is operational might overload the computer circuitry causing incorrect data in the circuitry or even failures in the circuit itself. This is because of the inherent impedance of the VDU.

Further problems are that other computers must be connected to their own VDU's, thus for example, in Glasgow there could be VDU's for computers in London, Liverpool, Manchester etc.

Since a VDU is an expensive item of equipment the present invention provides switching means which will enable the outputs from a number of computers to be selectively switched into a single VDU.

In Figure 1 there are illustrated six terminals 11,12,13,14,15 and 16, each of which is connected to receive an output signal from one of six computers (say A,B,C,D,E, and F). The terminals are connected to switches 21,22,23, 24,25 and 26 respectively, and these switches are ganged together so that they all move simultaneously on rotation of a master switch (not shown). Each switch has six positions, 1,2,3,4,5 and 6 (illustrated on switch 21) and in Figure 1 the switches are in position Number 1.

In this position it will be seen that computer A is connected through switch 21 to the input 30 of a VDU Computer B is connected to switch 22 which is also in position Number 1, and it will be seen that computer B is connected via a resistor 32 along line 37 and line 38 to the screening 46 at terminal 16. The screens 41 to 46 at each terminal are all connected together, and also via lines 38 and 39 to the screen 40 of the input 30 of the VDU. The line 39 is connected to the switching casing (effectively earth). Thus the output of computer B is connected to an impedance made up of resistor 32 and the screens 40-46 and this is substantially the same as the impedance of the VDU Computer B is not therefore affected by being disconnected from the VDU.

Similarly it will be seen that the outputs of computers C,D,E and F are also connected through resistors 33, 34, 35 and 36 to the screens 40-46 and are also similarly loaded by an impedance and are therefore unaffected by their disconnection from the VDU.

Rotation of the switches to position 2 connects the terminal 11 to a resistor 31 and thence again to the screen 4046. Hence computer A now has an impedance across it.

Terminal 12 is connected directly to the input 30 of the VDU, and terminals 13,14,15 and 16 are again connected via resistors 33,34,35 and 36 to the screens 4046. In position 2 therefore, only computer B is connected to the VDU.

Similarly, only computers C,D,E and F are connected to the VDU in switch positions 3,4,5 and 6 respectively. Thus only one computer at a time is connected to the VDU, the other five computers being located with the impedances formed by one of the resistors and the screens. The switches 21 to 26 are of the "make-before-break" type so that none of the computers or the VDU become open circuit during switching. Since the VDU can have an output when demanding information from one of the computers it is important that this also should not become open circuited.

In Figure 2, only two computer terminals 11 and 12 are shown from computers A and B.

In this case an extra switch 21a is included which switches the screen 41 at the terminal 11 into direct connection with the screen 40 of the VDU input 30 when computer A is switched to the VDU (switch position 1). As before the computer B output is loaded by the impedance made up of resistor 32 and screen 42. A similar switch 22a is included which operates in the same manner when computer B is connected to the VDU in switch position 2. The four switches 21, 21a, 22 and 22a are again all ganged.

In Figure 3 the three computer terminals 11, 12,13 are connected as in Figure 1, but three further computer terminals 1 ib, 12b and 13b are included which are intended to be connected to the input 30b of a printer (not shown).

Three further switches 21b, 22b and 23b are provided and these operate exactly as the switches 21,22 and 23 in that in switch position 1 the terminal 1 lb is directly connect ed to the input 30b of the printer, whilst the terminals 1 2b and 1 3b of computers B and C are connected via resistances 32b and 33b to the screens 40b43b.

The outputs from the computers to the printer thus do not go open circuit as the printer is switched from one computer to another.

The switches 21-23, 21 b-23b are ganged so that the printer is connected to the same computer as the VDU at any switch position.

WHAT WE CLAIM IS: 1. Switching means connected between a computer and a display unit between which electrical signals pass comprising a conducting member for the signals and an impedance circuit, the impedance circuit being connected to receive the signals immediately before the conducting member ceases to conduct the signals, and vice-versa.

2. Switching means as claimed in claim 1 in which the impedance value of the impedance circuit is at least as great as the impedance value of the display unit.

3. Switching means as claimed in claim 1 or claim 2 comprising a plurality of conducting members and a plurality of impedance circuits, the switching means being arranged to pass electrical signals between a plurality of computers and at least one display unit, the conducting members being arranged to conduct the electrical signals between at least one computer and a similar number of display units whilst the impedance circuits are connected to receive outputs from the remaining computers.

4. Switching means constructed and adapted to operate substantially as hereinbefore described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   30 of a VDU Computer B is connected to switch 22 which is also in position Number 1, and it will be seen that computer B is connected via a resistor 32 along line 37 and line 38 to the screening 46 at terminal 16. The screens 41 to 46 at each terminal are all connected together, and also via lines 38 and 39 to the screen 40 of the input 30 of the VDU. The line 39 is connected to the switching casing (effectively earth). Thus the output of computer B is connected to an impedance made up of resistor 32 and the screens 40-46 and this is substantially the same as the impedance of the VDU Computer B is not therefore affected by being disconnected from the VDU.

   Similarly it will be seen that the outputs of computers C,D,E and F are also connected through resistors 33, 34, 35 and 36 to the screens 40-46 and are also similarly loaded by an impedance and are therefore unaffected by their disconnection from the VDU.

   Rotation of the switches to position 2 connects the terminal 11 to a resistor 31 and thence again to the screen 4046. Hence computer A now has an impedance across it.

   Terminal 12 is connected directly to the input 30 of the VDU, and terminals 13,14,15 and 16 are again connected via resistors 33,34,35 and 36 to the screens 4046. In position 2 therefore, only computer B is connected to the VDU.

   Similarly, only computers C,D,E and F are connected to the VDU in switch positions 3,4,5 and 6 respectively. Thus only one computer at a time is connected to the VDU, the other five computers being located with the impedances formed by one of the resistors and the screens. The switches 21 to 26 are of the "make-before-break" type so that none of the computers or the VDU become open circuit during switching. Since the VDU can have an output when demanding information from one of the computers it is important that this also should not become open circuited.

   In Figure 2, only two computer terminals 11 and 12 are shown from computers A and B.

   In this case an extra switch 21a is included which switches the screen 41 at the terminal 11 into direct connection with the screen 40 of the VDU input 30 when computer A is switched to the VDU (switch position 1). As before the computer B output is loaded by the impedance made up of resistor 32 and screen 42. A similar switch 22a is included which operates in the same manner when computer B is connected to the VDU in switch position 2. The four switches 21, 21a, 22 and 22a are again all ganged.

   In Figure 3 the three computer terminals 11, 12,13 are connected as in Figure 1, but three further computer terminals 1 ib, 12b and 13b are included which are intended to be connected to the input 30b of a printer (not shown).

   Three further switches 21b, 22b and 23b are provided and these operate exactly as the switches 21,22 and 23 in that in switch position 1 the terminal 1 lb is directly connect ed to the input 30b of the printer, whilst the terminals 1 2b and 1 3b of computers B and C are connected via resistances 32b and 33b to the screens 40b43b.

   The outputs from the computers to the printer thus do not go open circuit as the printer is switched from one computer to another.

   The switches 21-23, 21 b-23b are ganged so that the printer is connected to the same computer as the VDU at any switch position.

   WHAT WE CLAIM IS: 1. Switching means connected between a computer and a display unit between which electrical signals pass comprising a conducting member for the signals and an impedance circuit, the impedance circuit being connected to receive the signals immediately before the conducting member ceases to conduct the signals, and vice-versa.
2. 2. Switching means as claimed in claim 1 in which the impedance value of the impedance circuit is at least as great as the impedance value of the display unit.
3. 3. Switching means as claimed in claim 1 or claim 2 comprising a plurality of conducting members and a plurality of impedance circuits, the switching means being arranged to pass electrical signals between a plurality of computers and at least one display unit, the conducting members being arranged to conduct the electrical signals between at least one computer and a similar number of display units whilst the impedance circuits are connected to receive outputs from the remaining computers.
4. 4. Switching means constructed and adapted to operate substantially as hereinbefore described with reference to the accompanying drawings.