`
`(12)UK Patent Application l19lGB (11)2 352 540 USA
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`(43) Date ofA Publication 31.01.2001
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`
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`(51)
`
`INT CL7
`soar 13/40
`
`(52) UK CL (Edition S l
`
`G4-A AFGDC
`
`(56) Documents Cited
`EP 0982563 A
`
`JP 100301898 A
`
`JP 100187303 A
`
`(21) Application No 99247694
`
`(22) Date of Filing 20.10.1999
`
`(30) Priority Data
`(31)
`9909849
`(32) 28.04.1999
`(33) GB
`
`(71) Applicant(s)
`Adder Technology Limited
`(Incorporated in the United Kingdom)
`Technology House, Trafalgar Way, Bar Hill,
`CAMBRIDGE, CB3 BSO. United Kingdom
`
`
`
`(58) Field of Search
`UK CL (Edition a ) G4A AFGDC AFGT
`INT CL7 GDSF 13/1213/33 13/40
`
`(72)
`
`(74) Agent and/or Address for Service
`|nventor(sl
`Urquhart-Dykes 8: Lord
`Adrian Christopher Dickens
`8th Floor, Tower House, Merrion Way, LEEDS,
`Nigel Anthony Dickens
`LS2 SPA, United Kingdom
`Mark Arthur Parr
`
`
`(54l Abstract Title
`Universal Serial Bus Switching Device
`
`(57) The switching device 100 connects a selected
`peripheral 114 to a selected one of three computers 112.
`The device comprises; a peripheral
`interface 160, USB
`computer interfaces 122, a switching means 140,142, a
`USB data transmission means 148 connectable between
`the peripheral
`interface and one of the USB computer
`interfaces by the switching means, a switching controller
`154 in communication with the switching means to control
`a switching event which connects the peripheral interface
`to one of the USB computer interfaces, a switching event
`request input device, which may be a keyboard 190, which
`when operated causes a switching event request signal
`180 to be communicated to the switching controller,
`causing the peripheral to be connected in communication
`with the selected one of the computers.
`The device allows two users to access three
`computers simultaneously using a keyboard, monitor,
`mouse
`and
`a
`group
`of USB peripherals whilst
`simultaneously supporting file transfer facilities between
`the computers.
`
`At least one drawing originally filed was informal and the print reproduced here is taken from a later filed formal copy.
`
`This print takes account of replacement documents submitted after the date of filing to enable the application to comply
`with the formal requirements of the Patents Rules 1995
`
`V0179Z982EIE)
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`
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`DELPHI Exhibit 1006
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`2352540
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`.1.
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`USB Switching Device and System
`
`The present invention relates to a switching device and a
`
`system including such a switching device, and in particular
`
`to a Universal Serial Bus switching device for use in
`
`connecting peripheral devices to a plurality of computers and
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`such a computer system.
`
`The Universal Serial Bus
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`(USB)
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`is a powerful and convenient
`
`way of connecting local peripherals to a host computer. The
`
`term ‘Universal Serial Bus’ relates to the hardware and
`
`software that allows a computer to be connected to, and to
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`operate with, a peripheral device.
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`The host computer
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`includes a controller that interfaces the computer with the
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`physical bus, along which signals travel, and to which
`peripheral devices can be attached.
`The transmission of data
`is controlled by a USB protocol which comprises a set of
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`rules, procedures and conventions relating to the format and
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`timing of data transmission between devices.
`
`The peripherals
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`are typically printers, scanners, keyboards, mice, speakers,
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`microphones, cameras,
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`joysticks and modems although other
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`peripheral devices are also supported. Multiple peripherals
`can be connected to a single shared Universal Serial Bus and
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`data transfer between the peripherals and the host computer
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`is achieved by allowing each peripheral to use time on the
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`USB bus in turn.
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`The flow of data across the Universal
`
`serial Bus is controlled by the host computer.
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`It is often desirable for cost, convenience and space saving
`
`reasons to share peripherals between groups of computers.
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`This can be achieved by using LAN connections such as
`
`Ethernet or by connecting cables from each computer to a
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`sharing device.
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`The wiring of such sharing devices is
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`reasonably straightforward if a single peripheral is to be
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`shared, as a single cable can be connected from the sharing
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`device to each of the computers.
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`If more than one type of
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`peripheral is to be shared,
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`then the wiring of such systems
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`becomes more complex as multiple cables will typically need
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`to be connected to each computer.
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`The number of cables
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`needed increases with the number of peripherals that are to
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`be supported.
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`For example, a device for sharing a keyboard,
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`mouse and printer between several computers would typically
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`need three cables to be connected between each computer and
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`the sharing device.
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`As the number of peripheral devices
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`increases, such systems become commercially impractical due
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`to the cost and complexity of the multiple sets of multiple
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`cables that are required.
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`The Universal Serial Bus can be exploited to help to overcome
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`these wiring difficulties by enabling a group of diverse
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`peripherals to be connected using a single common interface.
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`Such wiring simplification is particularly beneficial in
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`sharing applications that would otherwise required multiple
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`sets of multiple cables.
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`According to an aspect of the present invention there is
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`provided a Universal Serial Bus switching device for
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`connecting a peripheral to a one of a plurality of computers
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`comprising: a peripheral interface; a plurality of USB
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`computer interfaces; a switching means; a USB data
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`transmission means connectable between the peripheral
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`interface and a one of the plurality of USB computer
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`interfaces by the switching means;
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`a switching controller in
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`communication with the switching means to control a switching
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`event which connects the peripheral interface to a one of the
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`plurality of USB computer interfaces; and a switching event
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`request input device which when operated causes a switching
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`event request signal
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`to be communicated to the switching
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`controller, causing the peripheral to be connected in
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`communication with a one of the plurality of computers.
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`The invention can provide for the sharing of USB peripherals
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`between multiple USB host computers and provides a switching
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`system that takes advantage of the simpler USB wiring whilst
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`also allowing connection to multiple USB host computers.
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`The Universal Serial Bus is being adopted by a number of
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`different families of computers that previously used
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`USB ports can be found on
`different peripheral connections.
`many IBM compatible personal computers as well as a number of
`Apple Macintosh computers.
`The adoption of USB ports on
`other families of computers is likely in the future.
`The
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`invention therefore has advantages over more traditional
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`sharing solutions because it enables different types of
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`computers to be connected without having to support
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`conversions between different types of interfaces.
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`The Universal Serial Bus is primarily designed to connect a
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`group of up to 127 peripherals to a single host computer.
`Sharing peripherals between multiple hosts poses a number of
`difficulties because different types of peripherals are best
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`shared in different ways.
`The best sharing strategy for a
`particular type of peripheral will typically be application
`dependent.
`For maximum flexibility the data flowing between
`the computers and all the peripherals could be extracted from
`the USB signals and processed in a manner suitable for the
`application. However,
`the circuitry to achieve this data
`extraction is complicated and expensive and so the invention
`
`provides a simpler sharing strategy which is more appropriate
`
`for certain applications.
`
`One particular application for the invention that can be
`addressed by a simpler strategy is the sharing of a keyboard,
`monitor and mouse between several computer base units.
`
`Devices that perform this function are useful for
`conveniently accessing a group computers without
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`the need to
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`have a keyboard, monitor and mouse connected to each computer
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`base unit.
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`Such devices save on the power, space and
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`equipment needed and are particularly useful for computers
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`such as file servers that only need to be accessed
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`occasionally.
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`In keyboard, monitor and mouse sharing applications the
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`computer selection is under the control of the user and the
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`switching does not need to occur rapidly.
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`These
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`characteristics enable the current invention to be
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`constructed which can share the keyboard and mouse by
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`switching the associated Universal Serial Bus signals between
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`the host computers using a controllable USB switch. The
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`monitor can be shared straightforwardly by implementing a
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`video switching circuit.
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`The device can include a switching delay means,
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`in which the
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`switching delay means causes the switching controller to
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`prevent execution of a switching event until an enumeration
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`process between a peripheral and a currently connected one of
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`the plurality of computers has been completed.
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`The switching
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`of USB signals works because USB peripherals are designed to
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`be hot-pluggable and consequently the software within the
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`computers can typically detect the presence of the keyboard
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`and mouse when the USB signals are switched through and
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`configure the computers accordingly. The detection of
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`peripherals is accomplished by an enumeration process that
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`occurs when the USB connection is made. This enumeration
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`process typically takes of order one second or so to
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`complete, although the completion time increases with the
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`number of USB peripherals that are attached. Switching of
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`USB signals during the enumeration process is undesirable as
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`it can lead to erroneous messages being generated by the
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`computer and so is preferably avoided. However,
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`the device
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`and system can still function to an extent without
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`the
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`enumeration switching delay.
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`The current invention uses a switching controller circuit and
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`switching delay to ensure that switching of the USB signals
`does not occur during the enumeration process. The control
`circuit logs switching requests but only activates the
`control signal to switch the USB signals when it determines
`that it is safe to do so. Determination can be based on a
`
`simple time delay. Determination can be based on more
`sophisticated techniques in which the content of data passing
`between the USB peripherals and USB computers is monitored to
`determine when the enumeration process has been completed.
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`Only when the enumeration process is complete can the
`switching event be executed under control of the switching
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`controller.
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`The switching event request input device can include a
`manually operable control switch.
`The device can include a
`control panel.
`The device can include a display panel having
`a visual
`indicator which indicates which of the plurality of
`computers is currently connected to the peripheral by the
`device. The current invention enables the desired computer to
`
`be selected by pressing control panel key switches that
`communicate the switching event request signal to the
`switching controller circuit. The controller circuit in turn
`provides a signal to provide a visual indication of the
`selected computer unit on a display panel. This allows easy
`and straightforward computer selection when the user is
`
`located close to the device.
`
`1)
`input device can be a keyboard or
`The switching event request
`a mouse. Requesting a switching event by operating a control
`switch on the device is not convenient for applications where
`the device is located at some distance from the user's
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`
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`keyboard, monitor and mouse.
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`In the latter situations it is
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`preferable to be able to select the controlled computer using
`a keyboard and in particular a keyboard hotkey combination.
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`The implementation of keyboard control is not straightforward
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`because in order to achieve such control the data flowing
`from the keyboard needs to be analysed and ideally the data
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`corresponding to the hotkey combination needs to be removed
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`from the data stream so that it does not cause unwanted
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`effects on the currently selected computer. Due to the
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`complexity of the USB protocol such data analysis is costly
`to achieve by monitoring the USB signals.
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`Preferably the peripheral interface includes an emulator
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`which signals to a peripheral connected to the peripheral
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`interface using a peripheral protocol.
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`The current invention
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`overcomes the difficulty of monitoring all USB signals and
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`allows the keyboard data to be monitored and analysed by
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`implementing a peripheral interface circuit. The peripheral
`interface circuit emulates the presence of a USB peripheral,
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`and in particular a keyboard, on the Universal Serial Bus.
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`The emulator can include a PS/2 emulator means which
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`transmits PS/2 protocol signals to PS/2 peripherals connected
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`to the peripheral interface.
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`In this way PS/2 peripherals
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`can be connected to the device while still utilising a USB
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`based switching system to route USB data between the
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`peripherals and computers connected to the device.
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`The emulator can include USB emulator means which transmits
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`USB protocol signals to USB peripherals connected to the
`
`peripheral interface.
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`In this way USB peripherals will
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`behave as though connected directly to a USB host as the USB
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`protocol signals emulate the presence of a USB host to which
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`the USB peripherals have been connected.
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`The device can include a data extraction means which extracts
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`data in a USB independent format from peripheral data
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`transmitted between the peripheral and the device.
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`Preferably,
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`the peripheral interface includes a data
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`converter which converts data flowing within the peripheral
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`interface circuit between a USB dependent format and a USB
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`The data flowing to and from the
`independent format.
`keyboard is converted between USB signals and USB protocol
`independent data by a data converting means provided in the
`peripheral interface circuit. USB protocol
`independent data
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`can be taken as data that is transferred between two
`
`locations or otherwise processed without using the USB
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`protocol.
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`A switching event request signal can be communicated to the
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`switching controller in response to the extracted USB
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`independent data. The USB protocol
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`independent data can be
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`analysed and manipulated as required by a microprocessor
`function within the peripheral interface circuit to provide a
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`switching event request signal to the switching controller
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`circuit. The USB independent data which originates a
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`switching event request can correspond to a keyboard hot key
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`The microprocessor function monitors the data
`sequence.
`flowing through the peripheral interface circuit looking for
`data sequences corresponding to the keyboard hotkey codes.
`When these sequences are found the microprocessor function
`removes the data so that the hotkey codes are not sent to the
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`computer and then signals the corresponding switching event
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`request to the switching controller circuit.
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`The device can support USB peripherals and/or PS/2
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`peripherals. If a PS/2 keyboard is connected to the
`peripheral
`interface using a PS/2 connection then the signals
`transmitted between the keyboard and peripheral interface
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`include clock and data signals. The data flowing to and from
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`this keyboard is in a USB protocol independent format and can
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`therefore be analysed by the microprocessor function within
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`the peripheral interface circuit.
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`The peripheral interface can include a peripheral USB data
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`converter which converts peripheral data between the USB
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`independent format and the USB format. Circuitry in the
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`peripheral interface is provided which performs a data
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`conversion from the USB independent format used by PS/2
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`keyboards to the USB code format used by USB keyboards.
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`In the case of a USB keyboard connected via a USB connection,
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`the peripheral interface circuit contains the USB emulator
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`that emulates the presence of a USB host computer. This USB
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`host emulator also includes a USB data converter means which
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`converts the data flowing to and from the keyboard between
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`the USB protocol independent data within the peripheral
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`interface circuit and the USB signals used for communication
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`between the host emulator function and the USB keyboard. The
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`overall effect of this type of peripheral interface circuit
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`is therefore to convert the keyboard USB signals into a form
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`that can be analysed by the microprocessor function and then
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`convert these USB protocol independent signals back into USB
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`signals for communication with the currently selected host
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`computer.
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`The peripheral
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`interface can include a USB hub means in
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`communication with the peripheral data converter and in
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`communication with the USB data transmission means.
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`The
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`peripheral interface circuit preferably contains a USB hub
`function. This enables a group of USB peripherals such as
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`mice, speakers,
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`joysticks, printers, modems and cameras to be
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`shared together with the keyboard. The structure of this
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`arrangement is very advantageous because a flexible group of
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`other USB devices are automatically connected to the
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`currently selected computer without the need for additional
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`advanced circuitry. Because the USB signals between the host
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`and these peripherals are not disrupted once a connection has
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`been made, any USB peripheral device can be connected. This
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`enables the user to share a much more flexible group of
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`peripherals than would typically be practical using a non—USB
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`sharing device.
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`The device can include a plurality of peripheral interfaces
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`in communication with the USB data transmission means and
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`each peripheral interface connectable to a one of the
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`plurality of USB computer interfaces by the switching means.
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`Several USB keyboards and mice can be connected to the same
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`computer base unit and used simultaneously. An embodiment of
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`the current invention makes use of this characteristic in
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`order to implement a keyboard, video and mouse switching
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`device that supports two simultaneous users.
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`The same
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`principle can be used to support more than two users and so
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`systems supporting larger numbers of users are considered to
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`fall within the ambit of the invention.
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`The device can
`
`include a second switching means that operates under control
`
`of the switching controller in a similar way to the first
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`controllable switching means.
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`Each USB computer interface can include a USB hub means.
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`In
`
`order to enable the switching means to connect a peripheral
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`interface to any of the computers,
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`the device uses a group of
`
`computer interface circuits. Each computer is connected to a
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`computer interface circuit which implements a USB hub
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`function. This USB hub function creates a plurality of USB
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`downstream connections that provide the ability to connect
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`the USB switching means to the same computer. The peripheral
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`interface can be connectable by the switching means to an
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`input of each of the USB hub devices.
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`A plurality of
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`-10-
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`peripheral interfaces can be provided.
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`In this way an any—
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`to—any matrix switching structure can be created allowing any
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`of the connected user peripherals to control any of the
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`connected computers.
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`The robustness of operation of the device in practical
`applications is seen as an important characteristic that
`
`affects the desirability and value of the device and system
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`to the users. The error free operation of the computer
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`software during and after switch over of the USB switching
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`means is of particular importance. The device can include a
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`switching delay means that increases the reliability of
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`operation in a number of practical applications. However,
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`even with the switching delay means some anomalies are still
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`observed on some computer systems. A typical anomaly of this
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`type is failure of the computer software to detect one or
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`more of the USB peripherals that are attached to the USB hub
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`means after switch over of the USB switching means.
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`The device can include a peripheral connector device in
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`communication with the USB hub means and to which peripherals
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`can be attached,
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`the connector device being in communication
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`with the switching controller and operable under a control
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`signal to connect or disconnect
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`the USB hub and a peripheral
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`attached to the connector device.
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`The connector device
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`allows peripherals to be selectively connected to and
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`disconnected from.the USB hub at certain times during a
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`switching procedure thereby improving the robustness of
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`operation of the device. A.separate connector device can be
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`provided for each port of the USB hub.
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`The connector device
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`can connect or disconnect peripherals by controlling power
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`signals or data signals.
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`The USB peripheral connector device is used in conjunction
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`with the USB switching means to increase the robustness of
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`operation of the invention and consequently reduce the number
`of anomalies seen in some practical applications. The
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`peripheral connector device can be inserted into the links
`between the USB hubs means and the USB peripherals. The
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`peripheral connector device can be in communication with the
`switching controller and the switching controller can be in
`communication with the USB hub.
`The USB hub means is
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`intelligent and can detect the attachment or detachment of
`the USB peripherals to the USB hub by its downstream ports.
`By using the connector device together with the USB switching
`means the switching controller operate the switching means
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`and connect and disconnect peripherals attached to the USB
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`hub to effect a more reliable switching strategy.
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`A number of USB keyboards are fitted with a power on/off key.
`This power key enables the user to power on and power off the
`computer from the keyboard. Power on may be effected from a
`low—power suspended state that the computer goes into if it
`is switched off but still connected to the mains power.
`In
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`the power off signalling is
`one particular model of computer,
`achieved by transmitting a key press signal
`from the keyboard
`to the computer via the USB. The power on signalling is more
`complicated because the computer is not fully powered and the
`USB is therefore not fully active. The power on signalling is
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`therefore achieved by the keyboard connecting the USB data
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`to ground using a small resistor. This
`(D-)
`minus signal
`change is detected by the computer and causes the computer to
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`power up.
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`However,
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`this type of power on signalling is not transmitted
`
`through a USB hub and so the power on function of the power
`key is lost if the keyboard is connected to the computer via
`a standard USB hub.
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`The device can include a USB hub bypass which includes
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`switching means to selectively connect a peripheral device
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`connectable to the USB hub directly to a computer side of the
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`USB hub,
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`thereby bypassing the USB hub.
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`The hub bypass acts to bypass the hub under certain
`conditions and connect a single preferred USB downstream
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`connection of the hub directly to the computer side, USB
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`upstream connection of the hub whilst simultaneously
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`isolating the hub means. The requirement to bypass the hub
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`can be detected by monitoring the power
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`(Vbus) signal on the
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`USB upstream connection. This power signal is not active on
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`the USB connection from some computers whilst the computer is
`
`powered down so this signal can be used to detect when to
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`bypass the hub. The power signal can be used directly to
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`control the bypass means. Preferably the power signal is fed
`
`into a signal conditioning circuit to create a hub bypass
`
`control signal. The signal conditioning circuit can also take
`
`in information from other sources so that the hub bypass
`
`action can be prevented by the system.
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`The application of a hub bypass means is currently most
`
`relevant to Apple Macintosh computers and keyboards.
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`The
`
`same solution is applicable to any other computer keyboards
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`that implement similar power functions.
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`Each USB computer interface can include a USB data converter
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`and the device can include a bi-directional data transfer
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`means in communication with each USB computer interface and
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`providing bi-directional data transfer between computers
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`connected to the device via respective USB computer
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`interfaces.
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`The use of computer interface circuits has an
`
`associated advantage because the particular circuitry used to
`
`implement
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`them can also enable an additional
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`inter—computer
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`file transfer facility to be supported. This is achieved by
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`providing a USB data converter that implements a bi—
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`directional communications function within each computer
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`interface circuit that can convert USB signals into two-way
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`data that can be transferred between the various computer
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`interface circuits. This data transfer is achieved over a bi-
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`directional data transfer means using an IZC (Inter-IC
`
`Communication) bus that is connected to each computer
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`interface and enables any computer interface to send and
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`receive data from all other computer interfaces. When coupled
`
`with file transfer software running on each of the connected
`
`computers,
`
`this system enables files to be transferred
`
`between computers whilst simultaneously allowing peripherals
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`to be shared. This features makes the invention particularly
`
`useful for applications where a single keyboard monitor and
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`mouse is to be used to control a desktop PC and a laptop that
`
`are not otherwise networked together.
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`The device can include a computer video signal interface for
`
`receiving a computer video signal
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`from each of the plurality
`
`of computers,
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`a video signal output and a video signal
`
`switching means controlled by the switching controller and
`
`operable by the switching controller in response to a
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`switching event request signal to connect a computer video
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`signal
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`from a one of the plurality of computers to the video
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`signal output for display on a video display device connected
`
`to the video signal output.
`
`Preferably,
`
`the device includes
`
`a plurality of video signal outputs and the computer video
`
`signal interface including a computer video signal splitting
`
`means which splits each computer video signal into a number
`
`of signals corresponding to the number of video signal
`
`outputs,
`
`in which the video signal switching means provides a
`
`connectable path for a computer video signal from each of the
`
`plurality of computers to each video signal output.
`
`A matrix
`
`video switching circuit can be coupled to this USB switching
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`18
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`-14-
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`system so as to allow a video picture from a controlled
`
`computer to be switched together with the USB signals.
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`The device can enable three computers to be accessed from two
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`user stations that each support a keyboard, monitor and mouse
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`and a group of other USB peripherals. It will be appreciated
`that the invention is not limited to only three computers and
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`two user stations. The device can be used to control more or
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`less computers and may also have more or less user stations
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`that may have a mixture of characteristics such as the number
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`of USB downstream ports and the connectivity provided for the
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`controlling keyboard. Also, devices that have USB switching
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`facilities only and no video switching circuitry have a
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`number of uses. Consequently a wide variety of USB switching
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`systems are considered to fall within the ambit of the
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`current invention.
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`According to an aspect of the invention there is provided, a
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`Universal Serial Bus data transfer device for connecting a
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`peripheral to a one of a plurality of computers connected to
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`the device and transferring data between the plurality of
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`computers, comprising: a respective USB data converter for
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`each computer connected to the device and which converts USB
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`computer data communicated between the computer connected to
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`the USB data converter and the USB data converter between USB
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`computer data and a USB independent format data; a bi-
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`directional data transfer means in communication with each
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`USB data converter and providing bi—directional transfer of
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`USB independent
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`format data; a peripheral interface to which
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`the peripheral is connected; and a USB data transmission
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`means in communication between the peripheral interface and a
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`one of the plurality of USB data converters,
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`in which a
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`peripheral device connected to the peripheral interface can
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`be used to effect data transfer between any of the plurality
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`of computers connected to the device.
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`
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`19
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`-15-
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`An embodiment of the invention will now be described, by way
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`of example only, with reference to the accompanying drawings,
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`in which:
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`Figure 1 shows a functional block diagram of a device
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`and system according to aspects of the invention;
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`Figure 2 shows a functional block diagram of a video
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`signal switching part of the device; and
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`Figure 3 shows a schematic circuit diagram illustrating
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`a hub bypass part of the device.
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`The same items in different Figures share common reference
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`numerals.
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`The Figures show functional block diagrams only
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`and the location of the functional blocks is not
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`intended to
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`specify a particular configuration of separate devices.
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`The
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`block diagram merely indicates the functions performed and
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`the functional relationships of the functions. A.particular
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`function may be distributed amongst various real world
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`components and equivalently a number of functions, or parts
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`of different functions, may be realised by a single real
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`world component, e.g. a microprocessor and associated memory.
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`Figure 1
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`show a block diagram of a USB switching device,
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`designated generally by reference numeral 100, according to
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`the invention and a USB switching system, designated
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`generally by reference numeral 110,
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`including a plurality of
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`computers 112 and peripherals 118 connected to the device
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`100.
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`The example shown in Figures 1 and 2 is a device and
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`system that enables two users to control three computer base
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`units. Each user is able to connect a mouse 116 and other USB
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`peripherals 118 in addition to a keyboard 120 and monitor
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`122. According to the system,
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`these peripherals are then
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`connected via the device 100 to a one of the computer base
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`units 112 that is currently being controlled by the user's
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`keyboard and whose video is currently being displayed on the
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`
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`20
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`
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`__l6..
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`user's monitor.
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`For clarity,
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`the elements of the invention
`
`that are mainly concerned with controlling the switching
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`process and switching the USB signals are shown in Figure 1
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`and the elements that are mainly concerned with switching the
`video signals are shown in Figure 2.
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`With reference to Figure 1,
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`the USB switching device 100
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`includes a plurality of USB computer interfaces 122.
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`A one
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`of the plurality of computers 112 is connected to a
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`respective computer interface.
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`Each computer is connected to
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`the device via a Universal Serial Bus connection 124 that may
`include a USB hub 126. Each computer interface circuit 122
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`includes a USB hub function 128 and a USB computer data
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`converter and communications device 130. The USB hub 128
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`links to the computer 112 via an upstream connection 132 and
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`provides two downstream connections 134,136.
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`A bi-
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`directional data transfer means 138 is provided in
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`communication with the computer USB data converter and
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`communications device 130 of each of the computer interfaces.
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`Each computer interface circuit 122 can be implemented by a
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`Cypress CY7C66113 microcontroller and associated components
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`(not shown). The Cypress CY7C66113 is an 8-bit
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`microcontroller that contains integrated USB hub support and
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`can be used as a USB peripheral controller. The version used
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`to implement the preferred embodiment of the invention is a
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`one—time—programmable (OTP) part with internal RAM and
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`program memory.
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`The device includes a first and a second USB switching means
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`140,142.
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`The device includes a first and a second peripheral
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`interface 160,162. Each controllable USB switch 140,142 has
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`three upward connections 144 that are linked to the computer
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`interface circuits 122 and a downward connection 146 that is
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`linked to one of the peripheral interface circuits 160,162.
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`A USB data transmission means 148 is provided between each
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`21
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`-17..
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`peripheral interface 160,162 and any one of the computer
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`interfaces which is connectable by the USB switches 140,142.
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`The controllable USB switch 140,142 connects the USB data
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`signals (data + and data —)
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`from the downward connection 146
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`to one of the upward connections 144 according to a control
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`signal 150,152 communicated to the switch by a switching
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`controller 154.
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`The switching controller is in communication
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`with a switching delay means 156 which can delay a switching
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`event of the USB switches until an enumeration process has
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`been completed.
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`The controllable USB switch 140,142 is also
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`able to disconnect the