I IIIII IIIIIIII Ill lllll lllll lllll lllll lllll lllll lllll lllll 111111111111111111
`US007360004B2
`
`c12) United States Patent
`Dougherty et al.
`
`(IO) Patent No.:
`(45) Date of Patent:
`
`US 7,360,004 B2
`* Apr. 15, 2008
`
`(54) POWERING A NOTEBOOK ACROSS A USB
`INTERFACE
`
`(75)
`
`Inventors: Michael J. Dougherty, Houston, TX
`(US); Kenneth W. Stufflebeam,
`Houston, TX (US); Rahul V.
`Lakdawala, Cypress, TX (US);
`Thomas P. Sawyers, Hempstead, TX
`(US)
`
`(73) Assignee: Hewlett-Packard Development
`Company, LP., Houston, TX (US)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 470 days.
`
`This patent is subject to a terminal dis(cid:173)
`claimer.
`
`(21) Appl. No.: 10/674,923
`
`(22) Filed:
`
`Sep. 30, 2003
`
`(65)
`
`Prior Publication Data
`
`US 2004/0064621 Al
`
`Apr. 1, 2004
`
`Related U.S. Application Data
`
`(63) Continuation of application No. 09/608,082, filed on
`Jun. 30, 2000, now Pat. No. 6,668,296.
`
`(51)
`
`Int. Cl.
`G06F 13/00
`(2006.01)
`G06F 13/14
`(2006.01)
`G06F 1/26
`(2006.01)
`(52) U.S. Cl. ....................... 710/303; 710/305; 713/300
`(58) Field of Classification Search ................ 710/303,
`710/16; 713/300, 340
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`5,675,813 A
`5,841,424 A
`5,884,049 A *
`5,884,086 A *
`6,009,363 A *
`6,011,486 A *
`6,044,422 A
`6,046,571 A
`6,094,700 A
`6,105,097 A
`6,119,237 A *
`6,178,514 Bl*
`6,184,652 Bl*
`6,211,649 Bl
`6,281,784 Bl*
`6,283,789 Bl
`6,308,215 Bl
`
`10/1997 Holmdahl
`11/ 1998 Kikinis
`3/1999 Atkinson .................... 710/303
`3/1999 Amoni et al. ............... 713/300
`12/1999 Beckert et al.
`. .............. 701/33
`1/2000 Casey ....................... 340/7.29
`3/2000 Tran
`4/2000 Bovio et al.
`7 /2000 Deschepper et al.
`8/2000 Larky et al.
`9/2000 Cho ........................... 713/300
`1/2001 Wood ......................... 713/300
`2/2001 Yang .......................... 320/110
`4/2001 Matsuda
`8/2001 Redgate et al. ........ 340/310.01
`9/2001 Tsai
`10/2001 Kolbet et al.
`
`(Continued)
`
`OTHER PUBLICATIONS
`
`Universal Serial Bus Specification, Revision 2.0- Apr. 27, 2000-
`Section 7.2.1. *
`
`Primary Examiner-Rehana Perveen
`Assistant Examiner-Jeremy S. Cerullo
`
`(57)
`
`ABSTRACT
`
`A laptop computer and mating docking station where the
`docking station provides power to the laptop computer over
`power rails of the Universal Serial Bus (USB) interface. The
`laptop computer has laptop docking logic that both provides
`power in accordance with standard USB protocol, and also
`receiving power across the power rails of the USB interface.
`Likewise, the docking station has a docking station dock
`logic that establishes communication with the laptop dock(cid:173)
`ing logic across the USB power rails. Once positive com(cid:173)
`munication is established, the dock station provides voltages
`on the USB power rails sufficient to power the laptop
`computer as well as charge the laptop's battery.
`
`5,265,238 A
`
`11/ 1993 Canova et al.
`
`15 Claims, 3 Drawing Sheets
`
`134
`136
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`158
`144
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`-------------------------~
`
`COMMUNICATION
`AND
`CONTROL
`
`1 - - -~~
`
`NOTE:BOOK DOCKING
`COMMON STATION
`GROUND
`
`

`

`US 7,360,004 B2
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`6,357,011 B2
`6,362,610 Bl
`6,530,026 Bl *
`6,633,932 Bl *
`
`3/2002 Gilbert
`3/2002 Yang
`3/2003 Bard .......................... 713/320
`10/2003 Bork et al.
`................... 710/72
`
`......... 710/303
`6,668,296 Bl * 12/2003 Dougherty et al.
`4/2005 McClurg et al ............. 713/300
`6,886,104 Bl*
`2001/0034250 Al
`10/2001 Chadha
`
`* cited by examiner
`
`

`

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`
`150
`
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`
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`
`CONTROL
`
`VOLT
`
`

`

`U.S. Patent
`
`Apr. 15, 2008
`
`Sheet 3 of 3
`
`US 7,360,004 B2
`
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`L _________________________ J
`
`

`

`US 7,360,004 B2
`
`1
`POWERING A NOTEBOOK ACROSS A USB
`INTERFACE
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation of U.S. application Ser.
`No. 09/608,082, filed Jun. 30, 2000 now U.S. Pat. No.
`6,668,296, and entitled "Powering A Notebook Across A
`USB Interface."
`
`STATEMENT REGARDING FEDERALLY
`SPONSORED RESEARCH OR DEVELOPMENT
`
`Not applicable.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The present invention relates generally to docking a
`laptop computer to a docking station. More particularly, the
`invention relates to powering the laptop through the docking
`station when the laptop is in the docked position. More
`particularly still, the invention relates to powering the laptop
`across a USB interface when in the docked position.
`2. Background of the Invention
`Computer systems come in many shapes, sizes and com(cid:173)
`putational ability. For persons who work in designated
`locations, a standard desktop computer may be sufficient to
`fulfill that person's needs. However, for a user who travels
`frequently and needs computing power in those travels, a
`portable or laptop computer is desirable.
`Laptop computers are characterized in that the entire
`computing functionality is incorporated into a single pack(cid:173)
`age. That is, the motherboard, hard drive, disk drives, CD
`ROM drives, keyboard and display are all packaged in a
`compact device typically weighing less than ten pounds.
`Laptop computers are fully functional in that they may
`execute the very same programs, for example word proces(cid:173)
`sors and spreadsheet programs, as full sized or desktop
`computers. Laptop computers have a battery that allows for
`remote operation of the laptop even in locations where
`alternating current (AC) wall socket power is not available.
`While laptop computers may address portable computing 45
`needs, they are not without their limitations. For example,
`the keyboards of most laptop computers are a non-standard
`size. That is, the keys may be slightly closer together and not
`as ergonomically placed as a standard keyboard. Further,
`standard keyboards typically have function keys, cursor
`control keys and a full numerical keypad. In laptop com(cid:173)
`puters these keys are incorporated onto the standard keys by
`means of shift and function control. A further limitation of
`laptops, given the relatively small size, is they only have a
`limited number of communication ports available. That is, a 55
`laptop may support only a single parallel port, a single serial
`port and a single Universal Serial Bus (USB) port. Also, the
`display devices for laptop computers are typically small, as
`compared to desktop monitors, to keep the overall size of the
`laptop computer small.
`Many laptop users address limitations of laptops by some
`form of docking station. When the user returns to the home
`or office, the laptop is "docked" with a non-portable unit.
`Docking in this manner may expand the capabilities of the
`laptop computer to include a full size keyboard, a full size 65
`monitor, more serial ports, and other functionality typically
`associated only with desktop computing devices.
`
`25
`
`2
`The docking station can take many forms. For example,
`the docking station may extend one of the expansion buses
`within the laptop computer, e.g. a peripheral components
`interconnect (PCI) bus, to the docking station such that full
`5 computing functionality may be housed within the docking
`station. Expanding the PCI bus gives the docking station the
`ability to include a hard drive, expansion cards and the like.
`For laptop computers that dock to this type of docking
`station, the docking station typically provides power to the
`10 laptop within the docking connector between the laptop and
`the docking station.
`A second type of docking station, while extending the
`laptop's capabilities, it is not as extensive as the dock station
`that extends one of the expansion buses of the laptop. This
`15 second type docking station is commonly referred to as a
`port replication docking station. By port replication it is
`meant that by plugging the laptop into the docking station,
`more serial and parallel ports are available for connection to
`printers, scanners, full size display devices, serial or parallel
`20 pointing devices and the like. As with the full docking
`station explained above, these port replication docks typi(cid:173)
`cally also include power connections in the docking con(cid:173)
`nector.
`Another method of expanding the capabilities of a laptop
`may be a form of port replication across a USB port. A user
`connects a laptop, via a USB connection, to a port replica(cid:173)
`tion device which generates plurality of communication
`ports for use as described above. However, in situations
`where port replication is accomplished across the USB
`30 connector, the laptop user also plugs the laptop into a
`separate source of power, or operates the laptop on battery
`power. Given that the user most likely intends to use the
`laptop for an extended period of time in the location where
`port replication is desirable, a user of the such a system plugs
`35 the AC/DC power converter (also known as a power
`"brick") into a standard AC wall socket on its input and its
`output into the laptop computer. Thus, in this situation the
`user is required to plug in at least the USB expansion
`connection as well as a power cable. Also, there are prior art
`40 devices that have the appearance of a full docking station,
`that is the laptop may physically couple to a non-portable
`docking station where the act of docking couples the USB
`ports; however, these devices still require the user to sepa-
`rately apply power to the laptop.
`Thus, it would be desirable to have a USB based docking
`station that has the capability of both operating the laptop
`computer and charging the batteries in the laptop computer
`while docked without the need to plug in a separate power
`connection, thus reducing the time and complexity to couple
`50 the laptop to the docking unit. Despite the desirability of
`such systems, none are available in the prior art.
`
`BRIEF SUMMARY OF THE INVENTION
`
`The problems noted above are solved in large part by a
`laptop computer and related docking station adapted to
`supply power from the docking station to the laptop com(cid:173)
`puter across the USB connection. To accomplish this, the
`laptop computer is modified to have circuitry which is
`60 capable of being detected across USB power rails by the
`docking station and also capable of turning off the five volts
`typical supplied by the laptop onto the USB port, and
`instead, receiving power at 18.5 volts, from the docking
`station across the USB connections. The laptop computer
`may be operated by the dock unit supplied power and, if
`necessary, the laptop's battery may be charged. Likewise,
`the docking station contains circuitry coupled to the power
`
`

`

`US 7,360,004 B2
`
`3
`rails of the USB port which allows the docking station to
`detect whether the laptop computer coupled to the docking
`station is capable of receiving power.
`Thus, a laptop user need only plug the laptop into the
`docking station via the USB port, even if the battery for the 5
`laptop computer is drained. Once physically coupled to the
`docking station, the docking station detects whether or not
`the attached laptop is capable of receiving power across the
`USB port. If so, the docking station ramps power to the
`laptop computer to facilitate its operation.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`For a detailed description of the preferred embodiments of
`the invention, reference will now be made to the accompa(cid:173)
`nying drawings in which:
`FIG. 1 shows an exemplary computer system of the
`preferred embodiment;
`FIG. 2 shows a partial block diagram electrical schematic
`of a docked laptop and docking station; and
`FIG. 3 shows a more detailed electrical schematic of the
`reactive signaling circuit of the preferred embodiment.
`
`NOTATION AND NOMENCLATURE
`
`Certain terms are used throughout the following descrip(cid:173)
`tion and claims to refer to particular system components. As
`one skilled in the art will appreciate, computer companies
`may refer to a component by different names. This document
`does not intend to distinguish between components that
`differ in name but not function. In the following discussion
`and in the claims, the terms "including" and "comprising"
`are used in an open-ended fashion, and thus should be
`interpreted to mean "including, but not limited to ... ". Also,
`the term "couple" or "couples" is intended to mean either an
`indirect or direct electrical connection. Thus, if a first device
`couples to a second device, that connection may be through
`a direct electrical connection, or through an indirect elec(cid:173)
`trical connection via other devices and connections.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`The preferred embodiment of this invention, as illustrated
`in FIGS. 1-3, comprises a laptop computer 100 and an
`associated docking station 200. The computer system 100
`may be coupled to the docking station 200 and thus be in a
`"docked" configuration. Likewise, the computer system 100
`may be de-coupled from a docking station 200 and therefore
`be in an "undocked" configuration.
`FIG. 1 illustrates a laptop computer 100 in accordance
`with a preferred embodiment of the invention. Laptop com(cid:173)
`puter 100 generally includes a processor or CPU 102
`coupled to a main memory array 104 and a variety of other
`peripheral computer system components through an inte(cid:173)
`grated Host bridge logic device 106. The CPU 102 prefer(cid:173)
`ably couples to bridge logic 106 via a CPU bus 108, or the
`bridge logic 106 may be integrated into the CPU 102. The
`CPU 102 may comprise, for example, a Pentium® III
`microprocessor. It should be understood, however, that
`computer system 100 could include other alternative types
`of microprocessors. Further, an embodiment of computer
`system 100 may include multiple processors, with each
`processor coupled through the CPU bus 108 to the bridge
`logic unit 106.
`The main memory array 104 preferably couples to the
`bridge logic unit 106 through a memory bus 110, and the
`
`4
`bridge logic 106 preferably includes a memory control unit
`(not shown) that controls transactions to the main memory
`104 by asserting the necessary control signals during
`memory accesses. The main memory 104 functions as the
`working memory for the CPU 102 and generally includes a
`conventional memory device or array of memory devices in
`which program instructions and data are stored. The main
`memory array may comprise any suitable type of memory
`such as dynamic random access memory (DRAM) or any of
`10 the various types of DRAM devices such as synchronous
`DRAM (SDRAM), extended data output DRAM (EDO
`DRAM), or Rambus™ DRAM (RDRAM).
`The laptop computer 100 also preferably includes a
`graphics controller 112 that couples to the bridge logic 106
`15 via an expansion bus 114. As shown in FIG. 1, the expansion
`bus 114 preferably comprises an Advanced Graphics Port
`(AGP) bus. Alternatively, the graphics controller 112 may
`couple to bridge logic 106 through a Peripheral Component
`Interconnect (PCI) bus 116. As one skilled in the art under-
`20 stands, the graphics controller 112 controls the rendering of
`text and images on a display device 118. The graphics
`controller 112 may embody a typical graphics accelerator
`generally known in the art to render three-dimensional data
`structures on display 118. These data structures can be
`25 effectively shifted into and out of main memory 104 via
`bridge logic 106. The graphics controller 112 therefore may
`be a master of the expansion bus ( either PCI or AGP bus)
`enabling the graphics controller 112 to request and receive
`access to a target interface within the bridge logic unit 106,
`30 including the memory control unit. This mastership capa(cid:173)
`bility permits the graphics controller 112 to access main
`memory 104 without the assistance of the CPU 102. A
`dedicated graphics bus accommodates rapid retrieval of data
`from main memory 104. As will be apparent to one skilled
`35 in the art, the bridge logic 106 includes an AGP interface
`(not specifically shown) to permit master cycles to be
`transmitted and received by bridge logic 106. The display
`118 comprises any suitable electronic display device upon
`which an image or text can be represented. A suitable display
`40 device may include, for example, a liquid crystal display
`(LCD), a thin film transistor (TFT), a virtual retinal display
`(VRD), or any other type of suitable display device for a
`laptop computer system.
`The laptop computer system 100 preferably comprises
`45 another bridge logic device 120 that bridges the primary
`expansion bus 122 to various secondary buses including a
`low pin count ("LPC") bus 124 and the PCI bus 116. In
`accordance with the preferred embodiment, the bridge
`device 120 is an Input/Output Controller Hub ("ICH"). The
`50 ICH 120 supports the LPC bus 124, the PCI bus 116, the
`USB bus 126 as well as various other secondary buses,
`either directly or by way of further bus bridges.
`In the preferred embodiment of FIG. 1, the primary
`expansion bus 122 comprises a Hub-link bus which is a
`55 proprietary bus of the Intel® Corporation. However, laptop
`computer system 100 is not limited to any particular type of
`primary expansion bus 122, and thus other suitable buses
`may be used.
`The preferred embodiment of laptop computer 100 also
`60 has docking logic 134. Docking logic 134 is a set of circuitry
`coupled to the USB port 136 power lines 138. More spe(cid:173)
`cifically, the standard USB communication cable has four
`conductors. Two of these conductors are serial communica(cid:173)
`tion conductors 126 which allow communication between
`65 devices using USB protocol. The other two conductors carry
`power between USB devices. Under USB protocol, the
`power conductors 138 carry five volts. Referring to FIG. 1,
`
`

`

`US 7,360,004 B2
`
`20
`
`25
`
`5
`the laptop computer 100 of the preferred embodiment does
`not modify operation of the serial communication conduc(cid:173)
`tors 126 of the USB protocol. Preferably, all communica(cid:173)
`tions to establish whether laptop computer 100 is capable of
`receiving power from the docking station 200 take place 5
`over the power conductors or power rails 138 of the USB
`cable connector.
`FIG. 2 shows in more detail the docking logic 134 of the
`laptop computer 100 coupled to docking logic 234 of the
`docking station 200. Docking of these two logic circuits is
`preferably through USB connector 136 of the laptop com(cid:173)
`puter 100 and a mating USB connector 236 of the docking
`station 200.
`Under standard USB protocol, the laptop computer 100
`provides power to USB devices downstream of the laptop
`computer 100. Thus, in normal operation, the USB protocol
`voltage control unit 140 receives a five volt input signal 142
`which it couples to the positive power rail 144 of the power
`conductors 138. Downstream USB devices may draw cur(cid:173)
`rent through the positive power rail 144. If a user of the
`laptop computer 100 plugs in, for example, a USB mouse
`into the USB connector 136, that mouse under USB protocol
`may draw power across the power conductors 138 for its
`operational use.
`Assume for purposes of explanation that laptop computer
`100 has a charged battery and is in an operational state. In
`such a condition, the laptop computer 100 preferably pro(cid:173)
`vides five volt power across the power conductors 138.
`Further assume that the user docks the laptop 100 with a
`docking station 200 of the preferred embodiment. In so
`doing, the user either physically plugs in a USB cable to the
`connector 136 or slides the laptop computer 100 into a
`docking station 200. In this instance, with the laptop com(cid:173)
`puter 100 on and fully functional, the laptop computer 100
`attempts to provide power across the USB cable to the
`docking station 200.
`Under normal USB protocol, coupling of USB devices
`requires a series of USB handshaking protocols to identify
`both the host or master device, which would be the laptop
`computer 100, and any downstream device, which in this
`exemplary case is the docking station 200. In the preferred
`embodiment of this invention, this handshaking protocol
`between the laptop computer 100 and the docking station
`200 reveals to software running in the laptop computer 100
`that the docking station 200 is capable of providing power
`across the power rails 138 of the USB interface. It will be
`understood that this handshaking protocol between the lap(cid:173)
`top computer 100 and the docking station 200 occurs over
`the serial communication lines 126, and these lines are not
`shown in FIG. 2.
`Based on the handshaking between the two devices,
`operating system software loads a driver specifically used
`with the docking station 200. Though this driver may
`provide many functions, the function of concern is that the
`driver preferably turns off the laptop computer's ability to
`provide five volts to the power rails 138. More specifically,
`the driver loaded by the operating system of the laptop
`computer 100 preferably commands the Super I/0 controller
`130 to issue a five volt shut-off command signal 148,
`preferably through one of its digital outputs. This five volt
`shut-off command couples to the USB protocol voltage
`control unit 140 of the docking logic 134. Upon receiving
`this five volt shut-off command signal 148, the USB protocol
`voltage control unit 140 preferably de-couples the five volt
`input line 142 from the positive power rail 144. Thus, the
`
`6
`laptop computer 100 breaks with standard USB protocol and
`the power rails 138 are no longer capable of providing power
`to downstream devices.
`As far as docking logic 234 of the docking station 200 is
`concerned, the situation where laptop computer 100 turns off
`the five volt supply presents itself in the same manner as
`coupling a laptop computer 100 that either does not have a
`battery, and therefore is not operational, or whose battery is
`completely discharged. Thus, the following description is
`10 equally applicable to both situations. It is possible that
`laptop computers that do not have the capability of receiving
`power across the USB port may be docked with docking
`station 200. Therefore, docking station dock logic 234 must
`establish that the laptop computer to which it is docked is
`15 capable of receiving power. Preferably this is done by
`attempting to establish communications across the power
`rails 138 of the USB connector.
`Initially voltage ramp logic 210 (FIG. 2) provides no
`voltage whatsoever to the positive power rail 244 on the
`docking station 200 side of the connection. Upon detecting
`no voltage on the USB power rails, communication and
`control logic 250 commands the voltage ramp logic 210 to
`ramp-up a small voltage, preferably 3.1 volts, onto power
`rail 244. Positive power rail 244 couples to the power rail
`144 on the laptop side of the connection and therefore also
`couples to the reactive signaling circuit 150. Communica(cid:173)
`tion and control circuit 250 couples to reactive signaling
`circuit 150 across these power rails. In broad terms, the
`30 communication and control circuit 250 of the docking logic
`234 attempts to establish communication with the reactive
`signaling circuit 150 of the laptop docking logic 134. If
`communication and control circuit 250 establishes positive
`communication with reactive signaling circuit 150, the
`35 docking station 200 has made a positive identification that
`the laptop to which it is docked is capable of receiving
`power across the USB connection.
`More specifically, communication and control circuit 250
`preferably communicates with reactive signaling circuit 150
`40 by serially communicating across the positive power rail
`144. While there may be many protocols and devices
`capable of this communication, the preferred embodiment of
`the reactive signaling circuit 150 comprises a Dallas Semi(cid:173)
`conductor device part number DS2401, as shown in FIG. 3.
`45 This DS2401 has the characteristic that it stores charge
`drawn from its signaling line, and then, in response to a
`specific pattern of high and low voltages on its signaling
`line, transmits a series of high and low pulses across the
`signaling line to uniquely identify the device. Preferably, the
`50 communication and control logic 250 performs the neces(cid:173)
`sary steps to initiate communication with the DS2401 device
`and receives any return communication issued thereby.
`Upon receiving the communication from the DS2401 of
`the reactive signaling circuit 150, the communication and
`55 control circuit 250 preferably performs checks on the infor(cid:173)
`mation received to verify whether the laptop to which it is
`docked is capable of receiving power across the USB
`connection. Dallas Semiconductor makes another device, a
`DS2480, which is specifically made to communicate with
`60 the DS2401. However, in the preferred embodiment this
`device is not used and instead a Progranimable Array Logic
`("PAL") is used. A PAL has the characteristic that it may be
`field progranimed to execute certain steps or states and is
`therefore considered a field progranimable state machine.
`65 The PAL of the preferred embodiment performs all steps
`necessary to communicate with the reactive signaling circuit
`150 to establish positive identification that the laptop to
`
`

`

`US 7,360,004 B2
`
`7
`which the docking station 200 is docked is capable of
`receiving power across its USB connector.
`The connnunication and control logic 250, after positively
`identifying the laptop as capable of receiving power, informs
`the voltage ramp logic 210 across the ramp signal line 213
`to ramp the voltage on the positive USB power rail 244, 144
`up to approximately 18 volts. Voltage ramp logic 210
`couples to an 18 volt supply 212 which preferably comes
`from a power supply (not specifically shown).
`Voltage ramp logic 210, upon receiving the ramp indica(cid:173)
`tion from the connnunication and control logic 250, prefer(cid:173)
`ably ramps the voltage to 18 volts over a period of 20-50
`milli-seconds. Thus, the voltage on positive power rail 144
`with respect to the negative power rail 146 in the laptop
`computer begins to rise toward 18 volts. Laptop computer
`100 preferably operates using the 18 volt power supplied by
`the docking station 200 across the USB interface. Also, the
`laptop computer may charge its battery, if needed, with this
`same supply.
`It is possible that laptop computers that are not capable of 20
`receiving power across their USB interfaces may be coupled
`to the docking station 200. Indeed, it may be possible that a
`user quickly changes or swaps the USB connection from a
`laptop capable of receiving power to a laptop not capable of
`receiving power. The docking station 200 preferably detects
`that a computer user has de-coupled the USB port. Detection
`must be fast enough to insure that the dock station docking
`logic 234 removes the 18 volt power supply before the user
`couples it to another computer. This capability is preferably
`accomplished by a combination of functionality in the laptop
`docking logic 134, specifically the reactive signaling circuit
`150, and the dock station docking logic 234, specifically
`current sense logic 220.
`Reactive signaling circuit 150 in the laptop computer 100
`in combination with current sense logic 220 in the docking
`station 200 operate to detect that a user has unplugged or
`de-coupled the laptop computer 100 and the docking station
`200. More specifically, after voltage ramp circuit 210 of the
`docking logic 234 ramps voltage on the positive power rail
`244, 144 above a predetermined value, preferably 6 volts,
`the reactive signaling circuit 150 preferably draws a small
`amount of current from the docking station 200. This small
`amount of current, a coupling current, is detected by current
`sense logic 220 of the dock station docking logic 234. This
`small coupling current is monitored by the dock station
`docking logic 234 as an indication that two compatible
`devices remain coupled together. When the dock station 200
`provides power for full operation of the laptop computer
`100, as many as 2.5 amps of current may flow from the dock
`station 200 to the laptop computer 100 across the USB
`connectors 136, 236. The coupling current is part of that 2.5
`amp power flow. That is to say, when the laptop computer
`100 is operating from power supplied by the dock station
`200, the coupling current may be undistinguishable from the
`power drawn by the laptop.
`As long as current sense logic 220 detects at least an
`amount of current equal to the coupling current, the dock
`station docking logic 234 is assured that the laptop computer
`100 is capable of receiving power across the USB port. If the
`laptop computer system user unplugs the USB connection, 60
`or de-couples the laptop from the docking station, current
`sense logic 220 detects the loss of current flow and innne(cid:173)
`diately notifies the connnunication control logic 250 across
`logic line 252. Connnunication and control logic 250
`instructs voltage ramp logic 210 to cease providing power to 65
`the power rails 138 of the USB interface. Thus, the current
`sense logic 220, in combination with reactive signal circuit
`
`8
`150, assures a system user cannot dock a laptop that is not
`capable of receiving power to a powered USB port.
`Current sense logic 220 is preferably implemented with a
`Schottky diode in parallel with a resistor of small resistance.
`5 The voltage across this parallel combination is preferably
`detected by a comparator or operational amplifier whose
`output quickly saturates as current flow exceeds the coupling
`current minimum. One of ordinary skill in the art, now
`understanding the functionality of the current sense logic
`10 220, could implement many circuits to perform this function
`including the use of precision current sense resistors. Like(cid:173)
`wise, current logic 156, as indicated in FIG. 3, preferably
`comprises 1 kQ resistor coupled across the power rails.
`However, this 1 kQ resistance couples across the power rails
`15 only as the voltage on those rails reaches and exceeds the
`threshold voltage of 6 volts. Below the threshold voltage,
`which includes the voltage that the laptop supplies in
`conformance with standard USB protocol, the 1 kQ resis-
`tance does not draw current from the positive power rail.
`Because powering the laptop computer across the USB
`interface power rails requires voltages that may exceed
`breakdown voltages of the signaling device 152, the reactive
`signaling circuit 150 preferably also comprises a self-pro(cid:173)
`tection logic 154 coupled across the positive and negative
`25 USB power rails. The self protection circuit 154 electrically
`floats the signaling device 152 when the supply voltage
`exceeds the