United States Patent [19J
`De Nicolo
`
`111111111111111111111111111111111111111111111111111111111111111111111111111
`US006134666A
`[11] Patent Number:
`[45] Date of Patent:
`
`6,134,666
`Oct. 17, 2000
`
`(54) POWE R SUPERVlSOR FOR ELECTRONlC
`MODULAR SYSTEM
`
`[75]
`
`Inventor: Maurilio Ta zio De Nicolo, Saratoga,
`Calif.
`
`[73] As.signee: C isco Technology, [nc., San Jose, Calif.
`
`[2!] Appl. No.: 09/041,838
`
`[22] Filed:
`
`Mar. 12, 1998
`
`Int. C l.7
`[51]
`................... .. . . . . . . . ...... . ... ....... ......... . . G06F 1/26
`[52] U.S. C l . ........................... 713/300; 713/340; 713/330
`[58) Field of Search .............................. 710/ 2, 15, 16-19,
`710/101-103, 131, 132, 126-129; 713/300-340
`
`[56)
`
`References C ited
`
`U.S. PATENT DOCUMENTS
`
`4,835,737
`5,122,691
`5,226,120
`5,268,592
`5,386,567
`5,491,804
`5,613, 130
`5,632,021
`5,710,931
`5,726,506
`5,737,616
`5,758,102
`5,790,873
`5,796,185
`
`5/ 1989 Herrig et al. ........................... 364/900
`6/1992 Balak:risbman ......................... 307/475
`7/ 1993 Brown et al ............................ 395!200
`12/ 1993 Bellamy et al. .......................... 307/43
`1/1995 Lien et al.
`.............................. 39sn oo
`2/1996 lleatb ct al. ........•................... 395!275
`3/ 1997 Teng et al. . .... ... ... ... ... .... ...... ... 713/310
`5/1997 Jennings et al. ........................ 395/309
`1/1998 Nakamura et a l.
`..................... 7 J3/3l0
`3/ 1998 Wood ...................................... 307/ 147
`4/ 1998 Watanabe . .. . ............. ... ............ 713/340
`5/1998 Carey et al. ............................ 710!103
`8!1998 Popper et al. . ......................... 713/320
`8/ 1998 Takata et al. ........................... 307/ 140
`
`5,802,379
`5,809,256
`5,834,925
`5,845, 142
`5,884,233
`
`9/1998 Boatwright et al. .................... 713/324
`9/1998 Najemy ................................... 710/ 103
`11/ 1998 Cbesavage .............................. 323/272
`12/ 1998 Hayasaka ................................ 713/340
`3/1999 Brown ....................................... 702/61
`
`Primary Examiner-Ayaz R. Sheikh
`Assistant Examiner-Raymond Phan
`Allomey, Agent, or Firm--O'Alessandro & Ritchie
`
`[57]
`
`A BSTRACT
`
`Each modular processor card of a modular electronic system
`carries a component defining its maximum current or power
`requirements. The component, which may be a resistor,
`capacitor, serial access memory, or the like, is accessible
`over a single conductor through a backplane by a power
`supervisor. The supervisor will determine the current/power
`requirements of a processor card while the card is substan(cid:173)
`tially powered off. The supervisor may then weigh existing
`power supply resources of the modular electronic system
`with existing current/power demand and make a decision to
`allow power-up of lhe card if sufficient overhead is
`available, or, alternatively, make a decision to deny power(cid:173)
`up of the card if insufficient additional current/power
`resources are available. An oplional message indicating the
`outcome of the decision can be transm illed to a user. If the
`supervisor elects to power up I he card. a signal sent on the
`conductor connecting tbe card to the supervisor may be used
`to authorize tbe card to power up and control Circuitry to
`effect the power up.
`
`19 Claims, 2 Drawing Sheets
`
`BACKPLANE
`
`Vee
`
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`1
`I
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`I
`
`30
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`
`24
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`I
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`46
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`ENABLE
`
`I
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`:-------------- \--------------- -- - -- - - -_I
`
`26
`
`Page 1
` Dell Inc.
` Exhibit 1007
`
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`SUPPLY #N
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`
`POWER
`
`14
`
`20
`
`SUPPLY #2
`
`POWER
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`POWER
`
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`CIRCUIT ~A
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`
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`
`SOFT START
`
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`.---------------------------------------~
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`
`~-----------------------------
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`
`10
`
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`
`BACKPLANE
`
`t
`
`Page 2
`
`

`
`U.S. Patent
`
`Oct. 17, 2000
`
`Sheet 2 of 2
`
`6,134,666
`
`r---------------- ---- --- --- ---- -
`Vee )--..---..---V..:....+~e---n
`
`V A
`
`46
`
`42
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`ENABLE
`
`FIG.2
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`
`62
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`
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`
`POWER
`SUPERVISOR
`
`BACKPLANE
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`
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`COMMUNICATIONS I
`
`REGISTER
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`
`MODULE
`
`FIG. 3
`
`76
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`
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`BACKPLANE
`
`74
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`
`66
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`SUPERVISOR
`
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`
`PREST ART
`AREA
`
`MODULE
`
`~2
`
`FIG. 4
`
`Page 3
`
`

`
`6,134,666
`
`1
`POWER SUPERVISOR FOR ELECTRONIC
`MODULAR SYSTEM
`
`BACKGROUND OF T l IE INVENTION
`
`5
`
`2
`resources are available. An optional message indicating the
`outcome of the decision can be transmitted to a user. If the
`supervisor elects to power up the card. a signal sent on the
`conductor connecting tbe card to the supervisor may be used
`to authorize the card to power up and control circuitry to
`effect the power up.
`
`BRIEF DESCRIP110N OF THE DRAWINGS
`
`FIG. 1 is an electrical schematic diagram of a preseotly
`preferred embodiment of the present invention.
`FIG. 2 is an electrical schematic d iagram of a typical
`power so[! start circuit for use in conjunction witb a pres(cid:173)
`ently preferred embodiment of the present invention.
`FIG. 3 is a system block diagram of an alternative
`preferred embodiment of the present invention.
`FIG. 4 is a system block diagram of another alternative
`preferred embodiment of the present invention.
`
`DESCRJP'IlON OF THE PREFERRED
`EMBODIMENTS
`
`1. Field of the Invention
`The present invention is directed to a method and appa(cid:173)
`ratus which permit a power supervisor in a multi-card
`modular electronic system to tum on or off power to a given
`modular processor card based upon considerations of the 10
`power needed by the card and the power resources available
`to the modular electronic system.
`2. The Background Art
`Multi-card modular electronic systems are common in the
`computer ind\IStry. Typically such systems comprise a back 15
`p lane having a plurality of connectors to which a number of
`line cards or processor cards are connected . Processor cards
`may perform any of a number of functions as well known to
`those of ordinary skill in the art. The back plane provides
`e lectrical interconnections to the processor cards, such as 20
`data, power, ground and signalling. Such systems usually
`include at least one supervisor module which may be on one
`of the processor cards or may be permanently connected to
`the back plane. Supervisor modules arc commonly used to
`detect errors and report conditions to a user.
`It is desirable to build modular systems which provide (or
`future expansion while providing a relatively low corry cost.
`In systems employing processor cards which consume sig(cid:173)
`nificant quantities of power, such as those embodying one or
`more m-icroprocessors, or equivalently power hungry 30
`devices, it may be desirable to provide for modular power
`supplies which may be added or changed as power require(cid:173)
`ments increase with the addition of more processor cards or
`the subsriturion of higher power consumption processor
`cards for lower power consumption processor cards.
`In such systems, it is frequenrly a problem that an
`individual responsible for such systems may inadvertently
`place too high a power demand upon a particular power
`supply configuration of sucb a system through the addition 40
`of a particular processor card to a previously functioning
`system. The consequences can vary from a simple shut down
`or an inability to start up to equipment damage. Accordingly,
`it would be desirable to provide a method and apparatus
`which could simply protect such systems from the conse-
`quences of errors made by inadvertently overlooking avail(cid:173)
`able power supply resources in such modu.lar electronic
`systems.
`As back plane conductor lines are a relatively scarce and
`expensive resource in such systems, it would also be desir- 50
`able to implemeot sucb method and apparatus in a manner
`which makes a minimum use of such scarce resources.
`
`35
`
`Tbose of ordinary skill in the art will realize that the
`following description of the present invention is illustrative
`only and is not intended to be in any way l.imiting. Other
`25 embodiments of the invention will readily suggest them(cid:173)
`selves to such skilled persons from ao examination of the
`within disclosure.
`Turning io FIG. 1, a presently preferred embodiment of
`the present invention is shown. In accordance witb the
`present invention, a modular electronic system 10, such as
`computer communications equipment, bas a backplane ron-
`ncctor strip 12 whicb provides electrical interconnections
`among a plurality of electronic modules or cards which are
`electrically attached to it (e.g., plugged into it). The inven(cid:173)
`tion will work with one or more electwoic modules.
`In such modul ar electronic systems, one or more power
`supplies may be provided having certain power or current
`delivery capabilities. 1b render such systems more flexible,
`a plurality o( positions can be provided into wbicb such
`power supplies may be installed. The problem is that given
`a very fl exible level of power supply resources and a very
`flexible level of power demand posed by the electronic
`modules which may be attached to tbe backplane, the
`modular electronic system now must monitor both its
`resources and its power demand to insure that there is no
`shortfall of power which might cause system u.nreliability or
`failure.
`In accordance with a presently preferred embodiment of
`the present invention, a power supervisor 14 is provided.
`The power supervisor 14 has a communications link 16 to
`one or more power supplies 18, 20, 22 which communicates
`informat ion defining available power resources to a micro(cid:173)
`processor 24 of power supervisor 14. This communication
`ss may be carried out in any of a number of ways.
`According to a presemly preferred embodiment of the
`present invention, eacb power sup pi y module 18, 20, 22 may
`bave stored in it a relatively permancut memory having a
`three (or more) bit identiftcation code that can be read by
`60 power supervisor 14 over rommunications link 16. Each
`power supply 18, 20, 22 will have ils proper predefined
`identification code set at tbe time of its manufacture to a
`value unique for its model and/or indicative of its maximum
`ability to supply power or current. In typical use the power
`65 supervisor 14 will read the identificatio n code at power up,
`and/or at any time that the power supply module 18, 20, 22
`is inserted into or attached to power supervisor 14. Power
`
`45
`
`SUMMARY OF THE INVENTION
`
`Each modular processor card of a modular electronic
`system carries a romponent deliniog its maximum current or
`power requirements. The componeot, which may be a
`resistor, capacitor, serial access memory, or the like, is
`accessible over a single conductor through a backplane by a
`power supervisor. The supervisor will determine the current/
`power requirements of a processor card while the card is
`substantially powered oJI. 1be supervisor may then weigh
`existing power supply resources of the modular electronic
`system with existing current/power demand and make a
`decision to allow power-up of tl1e card if sufficient overhead
`is available, or, alternatively, make a decision to deny
`power-up of tbe card if insufficient additional current/power
`
`Page 4
`
`

`
`6,134,666
`
`3
`supervisor 14 then takes the identification code for the
`power supply module, and if necessary, looks up in a table
`as.wciated with power supervisor 14 the idemification code
`in order to determine a power output value for the power
`supply.
`In an alternative preferred embodimem, in order to pro(cid:173)
`vide more information without relying on software tables
`embedded in power supervisor 14, to serial electronically
`erasable programmable read only memory (EEPROM) is
`used in each J>OWer supply module 18, 20, 22. The serial
`EEPROM is preferably programmed at the time of manu(cid:173)
`facture of the power supply module with information apro(cid:173)
`pos of the power sup1>ly module, e.g., output voltages, input
`vohagcs, current levels, operating characteristics, model,
`type, seria l number, manufacturer, and the Like. This infor- 15
`matioo is then read at power up, or at insertion or allachment
`of the power supply module to power supervisor 14 so that
`power supervisor 14 is fu lly advised of the operati ng char(cid:173)
`acteristics of the power supply modules altached to it and
`can act on that information. A benefit of this Jailer approach 20
`is that new power supply modules can be created after power
`supervisor 14 Lc; fixed and installed and power supervisor 14
`can still make fu ll use of the information encoded in tbe
`serial EEPROM without any need for an upgrade or son(cid:173)
`ware update to the power supervisor. Other non-volatile 25
`memory devices could also be used instead of the serial
`EEPROM discussed above, as would be understood by those
`of ordinary skill in the art. Preferably such devices would
`use a single bit data path in order to minimize connections
`between power supervisor 14 and power supply modules 18, 30
`20, 22.
`Electronic module 26 auaches to backplane 12. Each
`electronic module will have a particular power requiremeOI.
`Obviously the power demand of module 26 will fluctuate
`depending upon what it is doing at a particular moment, but 35
`it will have a known maximum power requirement or
`demand which can be thought of as the worst case power
`requirement. It is thi'> known ma>.;mum power requirement
`that must be communicated to power supervisor 14.
`In accordance with a presentl y preferred embodiment of
`the present invention, tbc maximum power requ irement is
`communicated by an analog voltage signal on a query
`conductor 28 pas.~ ing from electronic module 26 through
`backplane 12 to power supervisor 14. Query conductor 28 is 45
`connected to a first source of a voltage, such as Vee 30
`through resistor Rl which may be a 100 ohm resistor.
`Analog to digital converter 32 converts the voltage on query
`conductor 28 to a digi tal value for use by programmed
`microprocessor 24. A component, such as an impedance 50
`clement, which may be a resistor, Rset 34, disposed between
`query conductor and a source of a second voltage 36, such
`as ground, encodes a voltage signal on query conductor 28,
`the voltage being a function of the resistance of resistor 34.
`For example, Rset 34 could be 25 ohms if power demand of 55
`the module is 5 amperes, 50 ohms if lO amperes, 75 ohms
`if 15 amperes, and 100 ohms if 20 amperes.
`The vohage drop between Vee 30 and query line 28
`through R 1 ic; selected to be sufficient to prevent current How
`through zcncr diode 0 1, thus isolating the portion of the 60
`circuitry of module 26 connected to the anode 38 of zcner
`diode from query line 28.
`If microproces.~or 24 decides that sufficient power
`resources arc available to permit module 26 to be turned on
`with its now known maximum power requi rement, then 65
`microprocessor 24 sends a signal .. PWRUP" on line 40 to a
`switch shown here as transistor QL The presence of the
`
`4
`PWRUP signal on the control gate of transistor Ql permits
`current to flow through Ql from Vee to query line 28. This
`voltage, not dropping through resistor Rl , will cause a
`higher voltage to obtain on query line 28. This voltage will
`be selected to be above the thresbold of zeoer diode 0 1. ln
`turn, current will How through resistors R2 and R3 providing
`a signal on a comrol gate of transistor Q2 which assumes the
`role of a switch. When this current flows, Q2 will rurn on and
`provide an ENABLE signal on line 42 to power circuit soft
`tO start 44.
`Power circuit soft start 44 operates in a conventional
`manner, such as that shown in FIG. 2 , to slowly turn on
`power available on line 46 and apply it to the power
`consumiog circuitry of module 26 denoted "A" while the
`ENABLE signal is asserted on line 42. Note that "'A" will be
`provided with a slightly lower voltage " V" than Vee (V+e)
`available at backplane 12 due to the voltage drop (e) through
`transistor Q3 which is preferably a power M OSFE']~ Cl is
`preferably O. l uF and C2 and C3 arc fi lter capacitors chosen
`based upon the application. The circuit shown io FIG. 2 is
`for reference only. An actual implementation would likely
`contain additional components needed to control the power
`s lope as known to those of ordinary skill in the art.
`Those of ordinary skill in the art: will realize that other
`components may be used to encode the maximum power
`demand of module 26 on query conductor 28. For example,
`capacitors, power supplies, and other elements having
`unique electrical characteristics capable of being read
`remotely over a single conductor could be used. Turning to
`FIGS. 3 and 4, a more sophisticated implementation of the
`present invention is shown. In FIG. 3 the component is a
`communications register 48. Power supervisor 50 commu(cid:173)
`nicates with communications register 48 over query line 52
`which passes through backplane 54. Module 56 also com-
`municates with communications register 48 over line 58.
`Power supervisor 52 may send messages to module 56 via
`communications register 48 which is preferably a one-bit
`wide data communications path. Communications register
`48 is preferably a serial register or serial access memory
`device or the like. Communications fro m power supervisor
`50 to module 56 may include, for example, messages along
`tbe lines of ··send yo ur maximum power requirement",
`·•send your model type" (so that tbc power supervisor could
`dctcrm inc from its pre-programmed memory what the maxi-
`mum power dema nd is), "go ahead aod start up", "do not
`start-maximum power exceeded", and tbe Like. Power may
`be provided to register 48 and module 56 during this
`pre-start period via line 60 connected to Vee 62 through
`backplane 54 as these devices typically require some mi ni(cid:173)
`mal amount of power in order to function. This minimal
`power, however, is negligible relative 10 the full maximum
`power requirement of the module 56.
`A soft-start circuit along the lines of F IG. 2 (or equivalent)
`would preferably be incorporated into Module 56. If a "go
`ahead and start up" signal is received by module 56, the
`soft-start circuit would be activated to bring the module on
`line.
`FIG. 4 shows a refinement of the embodiment of FIG. 3.
`In FIG. 4, power supervisor 64 communicates with module
`66 over a query line 68 which passes through backplane 70.
`Module 66 ic; provided with a prcstart area 72. Prestart area
`72 is provided with power over line 74 from a backplane
`connection 10 Vee 76. Prest art area 72's circuitry is powered
`by connection to line 74, but the bulk of the power(cid:173)
`consuming circuitry of modu le 66 remai ns unpowered until
`the prcstart area 72 receives instructions from power super-
`visor 64 to turn on modu le 66. The p restart area 72 may
`
`40
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`Page 5
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`

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`6,134,666
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`10
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`15
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`30
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`35
`
`5
`carry on extensive communications with power supervisor
`64 and power supervisor 64 may require information in
`addition to maximum power requirement-for example, a
`password could be required, or a particular range of serial
`numbers could be required. The power supervisor 64 could 5
`be programmed to disallow the power up of unauthorized
`devices or devices known to be incompatible with the
`particular modular electronic system in question. Some of
`these functions cou ld also be included in the FIG. 3 embodi-
`ment.
`In accordance with the various preferred embodiments of
`present invention the connections 10 a plurality or modules
`could be carried out with a plurality of query lines, each with
`a connection to the power supervisor, or with a single
`conductor connection to the power supervisor multiplexed to
`the plurality of modules in a conventional manner.
`It is intended that the system provided herein would be
`capable of "hot swapping" of module cards and/or power
`supply modules. In this manner, the system would be
`operating and an additional card would be plugged into a slot
`on the backplane. The power supervisor would detect the
`insertion of the card in a conventional manner and would
`query the module to determine if turning it on would exceed
`power resources available to the system. The system could
`also work without a "hot swapping" capability.
`The term ·'power" bas been used herein but is meant to 25
`include current level at a particular voltage, a combined
`power demand comprising a multiple voltage power demand
`at various currents, and the like, depending upon the system
`characteristics. For example, if aU power used by the module
`is at 3.3 V, then tbe only variable is current. However, if tbe
`module uses 3.3 V power as well as 5 V power, those of
`ordinary skill in the art will readily see bow the system
`described above could easily be expanded to cover a multi(cid:173)
`voltage system. While a multiplexing scheme, for example,
`could be used to scan for a number of different voltage
`requirements, or different voltage/current combinations
`could be encoded with a single component, multiple query
`conductors could also be used, if more convenient.
`The power supervisor may itself be a module p lugged into 40
`the backplane, o r it may assume ano the r physical
`embodiment, as long as it bas tbe required connections to tbe
`backplane conductors.
`Alternative Embodiments
`Although illustrative presently preferred embodiments 45
`and applications of this invention are shown and described
`herein, many variations and modifications are possible
`which remain within the concept, scope, and spirit of the
`invention, and these variations would become clear to those
`of skill in the art after perusal of this application. T he
`invention, therefore, is not to be limited except in tbe spirit
`of the appended claims.
`What is claimed is:
`1. A power management system
`a backplane to which a modular component may be 55
`connected, said modular component having an associ(cid:173)
`ated known maximum power demand;
`a query line having a first end and a second end connected
`together through said bacJ,"Plane, said first end adapted
`to connected to said modu lar component;
`a power supervisor attached to said backplane and to said
`second end, said power supervisor adapted to query
`said query Line and to receive therefrom an as.'>Ociated
`known maximum power demand of said modular
`component,
`wherein said power supervisor includes a ftrst voltage
`source coupled to said query line through a first
`
`6
`resistance, wherein said power supervisor senses said
`associated 1-."Tlown maximum power demand by sensing
`a voltage level on said query Line. wherein said power
`supervisor causes a selected voltage level to be applied
`to said query Line to cause said modular component to
`f11 lly power up, wherein said power supervisor gener-
`ates a power up signal which is sent over a line to a
`switch having a first state and :a second state, said
`switch allowing power to flow onto said query line
`when in said ftrst state and not allowing power to flow
`onto said query line when in said second state, said
`switch being in said second state in the absence of said
`power up signal and said switch being in said first state
`in the presence of said power up signal.
`2. A power management system according to claim 1
`wherein said switch includes a transistor having a control
`gate connected to said line.
`3. A power management system according to claim 2
`wherein said power supervisor further includes a digiti7:ing
`20 c lement coupled to said query line fo.r providing a digi tal
`representation of said voltage level to said power supervisor.
`4. A power management system for a modular electronic
`system comprising:
`a backplane to which a modular component may be
`connected, said modular component having a.n associ(cid:173)
`ated known maximum power demand;
`a query line having a first end and a second end connected
`together through said back."Plane, said first end adapted
`to connected to said modular component;
`a power supervisor attached to said backplane and to said
`second end, said power supervisor adapted to query
`said query line and to receive therefrom an associated
`known maximum power demand of said modular com(cid:173)
`ponent;
`a source of first information indicative of available power
`resources of the modular electronic system; and
`a source of second information indicative of existing
`power resource utilization of the modular electronic
`system, wherein
`the power management system is adapted to compare said
`first information, said second information and said
`associ.ated known power demand of sai.d modular com(cid:173)
`ponent to determine if sufficient power resources exist
`to successfully fully power up said modular compo(cid:173)
`nent.
`5. A power management system for a modular electronic
`system comprising:
`a backplane to which a modular component may be
`connected, said modular component having an as.'5oci(cid:173)
`ated known maximum power demand;
`a query line having a first end and a second end connected
`together th rough said backplane, said first end adapted
`to connected to said modular component;
`a power supervisor attached to said backplane and to said
`second end, said power supervisor adapted to query
`said query line and to receive therefrom an associated
`known maximum power demand of said modular com-
`ponent; and
`a source of first information indicative of excess power
`resources of the modular electronic system, wherein
`the power management system adapted to compare said
`information and said associated known power demand
`of said modular component to determ ine if sufficient
`power resources exist to successfully fully power up
`said modular component.
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`6. A power management system according to claim 5
`wherein said power supervisor includes a first voltage source
`coupled to said query line through a first resistance.
`7. A power management system according to claim 6
`wherein said power supervisor senses said associated known 5
`maximum power demand by sensing a voltage level on said
`query line.
`8. A power managemeat system according to claim 7
`wherein said power supervisor causes a selected voltage
`level to be applied to said query line to cause said modttlar 10
`component to fully power up.
`9. A power management system according to claim 8
`wherein said power supervisor generates a power up signal
`which is scot over a Line to a switch having a first state and
`a second state, said switch allowing power to flow onto said
`query line when in said first state and not allowing power to t5
`Dow onto said query line when in sa.id second state, said
`switch being in said second state in the absence of said
`power up signal and said switch being in said first state in the
`presence of said power up signal.
`HI. A power management system according to claim 9 20
`wherein said switch includes a transistor having a control
`gate connected to said line.
`11. A power management system according to claim 8
`wherein said power supervisor fu rther includes a digitizing
`element coupled to said query line for providing a digital 25
`representation of said voltage level to said power supervisor.
`12. An electronic modular component for connection to a
`modular e lectronic system including a backplane aod a
`power supervisor, said power supervisor having information
`indicative of remaining uncommitted electronic power 30
`resources of said electronic system, said modular component
`comprising:
`a query line conductor having a ftrst end and a second end,
`said first end connected to said backplane, said second
`end connected to a query node;
`a resistor having a first terminal connected to said query
`node and a second terminal connected to a source of a
`first voltage, said resistor's resistance indicative of a
`knovln maximum power demand of the electronic
`modular component, said resistor being able to be
`queried by the power supervisor while the electronic
`modular component is attached to the backplane; and
`a zcner diode having a breakdown voltage set to a second
`voltage, said zencr diode having a cathode connected to 45
`said query node and an anode operatively connected to
`a switch, said switch having a first state and a second
`state, said switch transmitting an enable signal to a
`power soft start circuit of the e lectronic modular com(cid:173)
`ponent when in said first state and not transmitting said
`enable signal when in said second state, said switch
`being in said second state in the absence of substantial
`current flow through said zener diode.
`13. A modular electronic system comprising:
`a backplane to which an electronic module having a 55
`known maximum power requirement is attached;
`a power supervisor connected to said backplane;
`a query conductor coupling a query node of said elec(cid:173)
`tronic modu le to said power supervisor through said
`backplane;
`encoder associated with said electronic module for pro(cid:173)
`viding signals to said power supervisor which are
`indicative of said maximum power requirement,
`wherein said encoding means comprises an electrical
`impedance e lement, wherein an e lectrical impedance is 65
`preselected to correlate with said known maximum
`power requirement; and
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`decoder associated with said power supervisor for decod(cid:173)
`ing said signals to determine said maximum power
`requirement.
`14. A modular electronic system according to claim 13
`wherein said electrical impedance clement is a first resistor.
`15. A modular electronic system according to claim 14
`wherein said signals which are indicative of said maximum
`power requirement are voltage signals produced by passing
`an electric current through said first resistor.
`16. A modular electronic system according to claim 15
`wherein said decoder comprises a programmed micropro(cid:173)
`cessor.
`17. A modular electronic system, comprising:
`a backplane to which an electronic module having a
`known maximum power requirement is attached;
`a power supervisor connected to said backplane;
`a query line conductor coupling a query node of said
`electronic module io said power supervisor through
`said backplane;
`encoding means associated with said electronic module
`for providing signals to said power supervisor which
`arc indicative of said maximum power requirement,
`said encoding means comprising a first resistor having
`a resistance preselected to correlate with said known
`maximum power requirement; and
`a programmed microprocessor associated with said power
`supervisor (or decoding said signals to determine said
`maJdmum power requirement, said signals being volt(cid:173)
`age signals produced by passing an electric current
`through said first resistor; said first resistor being
`connected between said query node and a source of a
`first voltage, said signals carried over a query conduc(cid:173)
`tor passing from said query node through said back(cid:173)
`plane and coupled through a second resistor to a source
`of a second voltage.
`18. A modular electronic system according to claim 17
`wherein a zener diode having a breakdown voltage set to a
`third voltage intem1ediate said ftrst voltage and said second
`voltage has a cathode connected to said query node and an
`anode operatively connected to a switch, said switch having
`a first state and a second state, said switch transmitting an
`enable signal to a power soft start circuit of tbc electronic
`module when in said first state and not transmitting said
`enable signal when in said second state, said switch being in
`said second state in the absence of substantial current flow
`through said zener diode.
`19. A method for authorizing the power up of a module
`connected to a backplane of a modu lar electronic system,
`said modular electronic system
`including a power
`supervisor, said method comprising the steps of:
`encoding information indicative of a maximum power
`requirement of the module;