`Volkswagen Group of America, Inc., Petitioner
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`1
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`U.S. Patent
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`Jan. 30, 1990
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`Sheet 1 of 10
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`4,897,642
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`U.S. Patent
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`Jan. 30, 1990
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`Jan. 30, 1990
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`Jan. 30, 1990
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`U.S. Patent
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`Jan. 30, 1990
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`Sheet 5 of 10
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`4,897,642
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`US. Patent
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`Jan. 30, 1990
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`Sheet 6 of 10
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`4,897,642
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`U.S. Patent
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`Jan. 30, 1990
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`Sheet 7 of 10
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`4,897,642
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`U.S. Patent
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`Jan. 30, 1990
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`Sheet 8 of 10
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`U.S. Patent
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`Jan.30, 1990
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`Sheet 9 of 10
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`4,897,642 S
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`U.S. Patent
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`Jan. 30, 1§90
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`Sheet 10 of 10
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`4,897,642
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`4,897,642
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`1
`
`VEHICLE STATUS MONITOR AND
`MANAGEMENT SYSTEM EMPLOYING
`SATELLITE COMMUNICATION
`
`BACKGROUND OF THE INVENTION
`
`The present invention generally relates to a method
`and apparatus for managing and monitoring the status
`of a fleet of vehicles. More particularly, the present
`invention relates to a method and apparatus for periodi-
`cally transmitting status and position data from a vehi-
`cle to a central station via satellite.
`The present invention has particular application to
`multiple part vehicles such as tractor-trailers of the type
`which comprise a tractor that can be detachably cou-
`pled to a trailer(s). However, the invention is also appli-
`cable to other types of vehicles such as railroad cars,
`buses, boats or ships and any other type of transporta-
`tion apparatus wherein it is desirable to monitor the
`status and location thereof on a regular basis.
`Fleet management is a major concern in the trucking
`industry. The fleet manager(s) must keep track of the
`status and location of each tractor and trailer in the
`fleet. Thus, for each trailer in the fleet, the fleet man-
`ager must know whether it is in service (i.e., coupled to
`a tractor) or out of service (i.e., not coupled to any
`tractor); the fleet manager musthave similar informa-
`tion with respect to whether each tractor in the fleet is
`hauling a trailer or is available for service. The fleet
`manager should also be able to monitor the progress of
`each vehicle in the fleet for scheduling purposes. Only
`with this information can the fleet be efficiently man-
`aged.
`Security is also a major concern to the fleet manager.
`Vehicle theft is commonplace in the trucking industry,
`and the fleet manager should be kept aware of unautho-
`rized use of vehicles. Moreover, it is desirable that the
`fleet manager have the capability of tracking the travel
`of a vehicle in unauthorized use so that law enforcement
`authorities can be kept apprised accordingly.
`The mechanical condition and various operating pa-
`rameters of each vehicle in the fleet are also of impor-
`tance to the fleet manager. The fleet manager should
`have regular access to operating parameters of the vehi-
`cle such as speed, engine temperature, oil pressure,
`brake line pressure and the like, as well as trailer param-
`eter data such as interior temperature and humidity of
`the trailer (if applicable) for each trailer that is in ser-
`vice. The fleet manager should also be immediately
`apprised of any abnormality in any of the operating
`parameters.
`Known systems and methods for accomplishing the
`foregoing are either expensive, impractical, inefficient
`or time consuming. It is therefore desirable to provide a
`vehicle status monitor and management system which
`accomplishes the foregoing which is simple, practical,
`inexpensive and easy to implement. The present inven-
`tion achieves these objectives.
`
`SUMMARY OF THE INVENTION
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`The present invention is described herein for particu-
`lar use on a tractor-trailer vehicle of the type compris-
`ing a tractor and a detachable trailer, but also has appli-
`cation to other types of vehicles. Accordingly, the fol-
`lowing description is not intended to limit application of
`the invention in any way to tractor-trailer vehicles and
`
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`2
`reference should be made to the appended claims for
`the true scope of the invention.
`A status monitoring system for a vehicle of the type
`comprising a tractor and a detachable trailer is pro-
`vided. As is known, the tractor has a power bus with a
`power cable that is connectable to the trailer when the
`trailer is coupled to the tractor. As is also known, the
`trailer has a power bus that is energized and electrically
`coupled to the tractor’s power bus when the power
`cable is connected thereto. According to the invention,
`the status monitoring system comprises a tag (identify-
`ing apparatus), an interface unit (IFU) and a mobile
`satellite transmitter (MST). The tag is mounted on or in
`the trailer and electronically impresses an ID code on
`the trailer’s power bus when the power bus is energized.
`(Alternatively, the tag may communicate ID code data
`by other means such as infrared, acoustic, RF or other
`electromagnetic transmitters.) The ID code is unique
`and identifies the trailer. The IFU detects the presence
`of a valid ID code that appears on the tractor’s power
`bus (or in the particular transmission medium em-
`ployed) when the power cable is connected to the
`trailer. When a valid ID code is detected, the IFU pro-
`vides a status indication that a trailer is connected to the
`tractor; similarly, when a valid ID code is not con-
`nected, the IFU provides a status indication that no
`trailer is connected to the tractor. The IFU may be
`situated within the tractor’s cab or tool compartment,
`or wherever convenient.
`
`The MST is also preferably situated within the trac-
`tor’s cab or tool compartment or wherever convenient
`and may be of the type that includes a position locating
`unit, for example, of the type employing LORAN. The
`MST receives the status indication from the IFU and
`may also receive vehicle position data from the position
`locating unit, if provided. The MST transmits at least
`the status indication, and the ID code if available, at
`preselected (preprogrammed) intervals to an earth sta-
`tion via a space-based satellite. The MST operates
`under control of the IFU to normally transmit the status
`indication (and vehicle position data, if provided) at the
`preselected intervals, but is responsive to a command
`from the IFU to substantially immediately transmit (i)
`the status indication (and vehicle position data, if pro-
`vided) when the presence of a valid ID code is initially
`detected (thereby indicating that a trailer has initially
`been connected to the tractor), and (ii) the status indica-
`tion and the last detected ID code when the lack of a
`valid ID code is initially detected (thereby indicating
`that a trailer has initially been disconnected).
`The MST may alternatively be of a type that does not
`include a position locating unit. Rather,
`the RDSS
`(radio determination satellite system) may be employed
`to determine the location of each MST, and hence its
`associated vehicle, when an MST transmission occurs.
`As is known, the RDSS uses the actual transmission
`from a satellite transmitter (such as the MST) to pin-
`point its position. Position is computed at the satellite
`and provided to the earth station. Thus, as in the case of
`an MST equipped with a position locating unit, each
`MST transmission results in vehicle position data that is
`provided to an earth station, even though in one case
`the position data is generated by the MST and in the
`other case is generated by the satellite.
`According to the preferred embodiment of the inven-
`tion, the trailer’s power bus is modulated with the ID
`code so that the same appears on the tractor’s power bus
`when the two are connected. According to one pre-
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`each MST transmission always results in vehicle posi-
`tion data being provided to an earth station.
`Other features of the invention will be apparent from
`the following detailed description of the preferred em-
`bodiment and from the appended claims.
`For a full understanding of the present invention,
`reference should be made to the following descriptio
`and to the accompanying drawings.
`‘
`
`3
`ferred embodiment, the tag is “dumb” and repeatedly
`and cyclically impresses the ID code on the trailer’s
`power bus; the IFU monitors the tractor’s power bus to
`determine whether a valid ID code has been impressed
`thereon. According to another embodiment, the tag is
`“smart” and the IFU requests ID code data from the
`tag. The tag may be provided with inputs for trailer
`sensors that provide trailer parameter data. If provided,
`the tag further impresses the trailer parameter data on
`the trailer’s power bus so that the IFU can read the
`trailer parameter data from the tractor’s power bus and
`provide the same to the MST for transmission to the
`earth station. The tag may also be responsive to a field
`programmer connectable to the power bus to alter the
`ID code stored therein and/or change the tag’s operat-
`ing program.
`According to yet another embodiment of the inven-
`tion, the IFU may be provided with inputs for tractor
`sensors that provide tractor parameter data. If pro-
`vided, the IFU reads the tractor parameter data and
`provides the same to the MST for transmission to the
`earth station.
`
`The IFU may also be provided with an input for
`receiving an alarm signal from a vehicle protection
`device, and, if provided, the IFU provides any alarm
`indication to. the MST for transmission to the earth
`station. According to this embodiment, the MST oper-
`ates under control of the IFU to normally transmit the
`status indication (and vehicle position data, if provided)
`at the preselected intervals, but is responsive to a com-
`mand from the IFU to substantially immediately trans-
`mit an alarm indication (and vehicle position data, if
`provided) when an alarm signal is received by the IFU.
`Also, according to this embodiment, the MST may be
`responsive to commands from the IFU to substantially
`immediately transmit tractor and/or trailer parameter
`indications (and vehicle position data,
`if provided)
`when an abnormality in any of the tractor/trailer pa-
`rameter data or a security violation (e.g., from the vehi-
`cle protection device) is detected by the IFU.
`According to a preferred embodiment of the present
`invention, the tag (identifying apparatus) comprises a
`code generator for providing a digital ID code that is
`unique to the vehicle, a short haul modem for modulat-
`ing the code at a preselected baud rate, and a transmit-
`ter/buffer for impressing the modulated code on an
`existing electrical system (power bus) of the vehicle. As
`mentioned,
`the tag may alternatively employ other
`available or specially installed lines or other communi-
`cation means for communicating the ID code.
`A method of monitoring the status of a multiple-part
`vehicle according to the present invention comprises
`the steps of impressing a unique ID code on an existing
`electrical system (power bus) of the vehicle when a
`second part of the vehicle is connected to a first part of
`the vehicle; detecting whether a valid ID code has been
`impressed on the vehicle’s existing electrical system;
`providing a status indication representing the connect-
`/disconnect status of the second part of the vehicle
`based upon the aforementioned detecting step; transmit-
`ting the status indication, and also the ID code if a valid
`ID code has been detected, to a central station at regu-
`lar preselected intervals; and, transmitting the status
`indication and ID code to the central station substan-
`tially immediately upon any change in the status indica-
`tion. Each transmission to the central station may in-
`clude vehicle position data therewith if the MST is of
`the type employing a position locating unit. However,
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`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a diagrammatic view of a preferred embodi-
`ment of the present invention as utilized in a tractor-
`trailer.
`
`FIG. 2 is a overview of a preferred embodiment of
`the present invention in block diagram form.
`FIG. 3 is a block diagram of one preferred embodi-
`ment of a tag (identifying apparatus) according to the
`present invention. '
`FIG. 4 is a block diagram of another preferred em-
`bodiment of a tag (identifying apparatus) according to
`the present invention.
`FIG. 5 is a block diagram of an IFU according to the
`present invention.
`FIG. 6 is a flow chart providing an overview of the
`IFU function.
`
`FIG. 7 is a flow chart illustrating the function of a tag
`according to one preferred embodiment of the inven-
`tion.
`
`FIG. 8 is a flow chart illustrating the function of a tag
`according to another preferred embodiment of the in-
`vention.
`
`FIGS. 9A—9C are flow charts illustrating in greater
`detail the function of an IFU according to a preferred
`embodiment of the invention.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`Referring now to the drawings wherein like numerals
`represent like elements, there is illustrated in FIG. 1 a
`tractor-trailer vehicle 10 comprising a tractor 12 and a
`detachable trailer 14. Tractor 12 includes a cab 13. As is
`well known, tractor 12 is adapted to be coupled to one
`of a plurality of trailers 14 in a fleet. As is also well
`known, tractor 12 includes a l2-volt battery 16 that
`energizes a 12-volt power bus (existing electrical sys-
`tem) 18 that runs throughout the tractor. As is also
`known, trailer 14 comprises a normally de-energized
`power bus (existing electrical system) 20 that runs
`throughout trailer 14. When trailer 14 is mechanically
`coupled to tractor 12, the trailer’s power bus 20 is ener-
`gized and electrically coupled to the tractor’s power
`bus 18 by means of the tractor’s power cable 22 that is
`connectable to the trailer 14. Thus, in normal operation,
`when trailer 14 is coupled to tractor 20, the trailer’s
`power bus 20 is energized, and when the trailer 14 is not
`connected to a tractor 12, its power bus 20 is not ener-
`gized.
`According to the invention, each trailer 14 in the fleet
`is provided with an electronic tag 24 (identifying appa-
`ratus) and each tractor 12 is provided with an interface
`unit (IFU) 26 that communicates with an on-board mo-
`bile satellite transmitter (MST) 28. MST 28 is coupled
`to a microwave antenna 32 for transmitting messages to
`an earth station via a space-based satellite. In the pre-
`ferred practice of the invention, the MST 28 transmits
`messages to the well known GEOSTAR satellite(s) that
`is currently in geosynchronous orbit above the conti-
`
`13
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`5
`nental U.S. See U.S. Pat. Nos. 4,359,733 and 4,744,083
`incorporated herein by reference.
`The tag 24, IFU 26 and MST 28, and the manner of
`communication therebetween, will now be described in
`greater detail with reference to FIG. 2.
`As explained in more detail herein, tag 24 communi-
`cates with IFU 26 for the purpose of providing ID code
`data when the trailer’s power bus 20 is energized and
`coupled to the tractor’s power bus 18 by power cable
`22. An important feature of the invention is that the tag
`24 and IFU 26 communicate with each other by means
`of the power bus 18, 20 (including the power cable 22
`connecting them) sothat 11 additional wiring or inter-
`connections are necessary, although other means and
`methods of communication are not precluded. Thus, the
`tag 24 and the IFU 26 preferably use the vehicle’s exist-
`ing electrical system for communication therebetween
`but other means such as infrared, acoustic, and RF
`receivers and transmitters can be employed. Thus, it
`should be understood that although the following de-
`scription refers to use of the vehicle’s existing electrical
`system for communication between the IFU and the
`tag, the present invention is not limited thereto except
`as set forth in the appended claims.
`The function of tag 24 is to provide signals contain-
`ing, inter alia, a unique ID code when the trailer’s
`power bus 20 is energized, i.e., when the trailer 14 is
`coupled to the tractor 12. The tag 24 impresses signals
`containing the ID code on the trailer’s power bus 20 via
`connection 34. Since the trailer’s power bus 20 is cou-
`pled to the tractor’s power bus 18 by power cable 22,
`these signals also appear on the tractor’s power bus 18.
`IFU 26 is coupled to the tractor’s power bus 18 by
`means of connection 30. The fimction of IFU 26 is to
`detect the presence of a valid ID code on the tractor’s
`power bus 18 and, when a valid ID code is detected
`(indicating that a trailer 14 is connected to tractor 12)
`provide a status indication to this effect, and likewise
`when a valid ID code is not detected (indicating that no
`trailer 14 is connected to tractor 12) provide a status
`indication to this effect. The IFU 26 provides the status
`indication and, when detected, the ID code, to MST 28
`via a connection 36. The MST may preferably include
`position locating unit (discussed below), though not
`necessary. The MST receives the status indication from
`the IFU and transmits it at preselected intervals to an
`earth station via a space-based satellite. If the MST
`includes a position locating unit, then vehicle position
`data is included in each MST transmission. If the MST
`is of a type that does not include a position locating unit,
`then the RDSS may be employed to pinpoint vehicle
`position based upon the MST transmission. In either
`case, the earth station is provided with both the status
`indication and vehicle position data, and the ID code if
`detected.
`
`The MST may be of any well known type, but in the
`preferred embodiment of the invention is a Hughes
`Network Systems Model No. 2101 or 2102. A Sony
`Corporation Wafarer Mobile Communication Unit,
`SCD 1000 Series, may also be used. Each of these units
`includes a microwave transmitter and an antenna 32 for
`the purpose of transmitting messages to the GEOSTAR
`satellite. Each also presently includes a position locating
`unit in the form of a LORAN C receiver and a com-
`puter for processing internal data, and commands and
`data from an external source, in this case the IFU 26.
`Preferably, the data and commands from the IFU 26 are
`provided via a serial link 36 to a serial (RS 232) port on
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`the MST 28. Future MSTs may not include a position
`locating unit and may instead rely upon the RDSS for
`position data.
`The above-identified MSTs are capable of sending I
`three different types of transmissions (messages) that are
`"recognized by the GEOSTAR satellite. These are
`NORMAL, IMMEDIATE and EMERGENCY. In
`the absence of a command to the contrary, the MST
`transmits NORMAL messages at regular preselected
`intervals; the duration between intervals is user select-
`able (programmable). The MST operates under control
`of the IFU to normally transmit the status indication
`(and vehicle position data when provided) by means of
`NORMAL messages at the preselected intervals. How-
`ever, the MST is responsive to a command from the
`IFU to substantially immediately transmit either an
`IMMEDIATE or EMERGENCY message containing
`the status indication (and vehicle position data when
`provided). GEOSTAR stores NORMAL and IMME-
`DIATE messages in an electronic mailbox that is polled
`on an as-needed basis by the user (in this case, the fleet
`manager) who resides at a central station. EMER-
`GENCY messages are not stored in a mailbox; rather,
`GEOSTAR requests IMMEDIATE acknowledgement
`of EMERGENCY messages from the fleet manager.
`The NORMAL, IMMEDIATE and EMERGENCY
`modes of transmission are utilized by the present inven-
`tion as described below.
`The above-identified MSTs also have their own iden-
`tifier which is included with every transmission to
`GEOSTAR. Moreover,
`the above-identified MSTS
`include an internal clock and each transmission is ac-
`companied by data indicating the time of the transmis-
`sion.
`
`Returning again to FIG. 2, the tag 24 may, if desired,
`be provided with inputs for receiving signals from one
`or more trailer sensors. Thus, information respecting
`the interior temperature and humidity of the trailer, and
`other critical parameters may be provided to the tag 24.
`As explained herein, when tag 24 is provided with such
`capability, the information is impressed on the power
`buses 18, 20 for reading and processing by the IFU 26
`and transmission by the MST 28. Additionally, if de-
`sired, the IFU 26 may be provided with inputs for re-
`ceiving signals from one or more tractor sensors 40.
`Tractor sensors 40 may provide information regarding
`tractor operating parameters such as speed, engine tem-
`perature, oil pressure and the like. IFU 26 may if de-
`sired, provide such information to MST 28 for inclusion
`with each transmission. IFU 26 may also receive as an
`input an alarm signal provided by a vehicle protection
`device 42 on board tractor 12. Preferably, vehicle pro-
`tection device 42 is of the type described in U.S. Pat.
`No. 4,691,801, but any suitable vehicle protection de-
`vice will suffice. In response to an alarm signal, the IFU
`26 may provide an alarm indication to the MST 28 for
`transmission in one of the NORMAL, IMMEDIATE,
`or EMERGENCY modes, as desired, however trans-
`mission in one of the IMMEDIATE or EMERGENCY
`modes is preferred. Likewise, IFU 26 may be responsive
`to an abnormal tractor or trailer condition, as indicated
`by one of the trailer sensors 38 or tractor sensors 40, to
`cause the MST 28 to transmit the indication of the ab-
`normal condition in one of the IMMEDIATE or
`EMERGENCY modes.
`
`Turning now to FIG. 3, one preferred embodiment of
`a tag according to the present invention is depicted. The
`tag 24 depicted in FIG. 3 is “dumb” in that it is unidirec-
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`4,897,642
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`7
`tional and its sole function is to repeatedly and cycli-
`cally generate an ID code and impress signals contain-
`ing the ID code on the power bus 20. As shown, tag 24
`comprises a code generator 44 that provides serial code
`data over a line 62 to the transmit data (TD) input of a
`modem 46. Code generator 44 and modem 46 receive
`clock pulses from a clock 50. A short haul modem 46
`modulates the serial code data and provides the same at
`the transmit carrier output (TC) for transmission over a
`line 64 to a transmitter/buffer 48. The transmitter/-
`buffer 48 impresses the modulated data on power bus 20
`by means of connection 34. The transmitter/buffer 48,
`modem 46, code generator 44 and clock 50 are powered
`by a power supply 52 that receives its power input from
`the power bus 20. Thus, the tag 24 is not functional until
`the power bus 20 has been energized.
`The code generator 44 of the tag 24 performs the
`function of repeatedly and cyclically generating the
`unique ID code. According to a preferred embodiment
`of the tag 24, the code generator 44 comprises a divider
`(counter) 54 receiving clock pulses from the clock 50.
`Clock pulses of reduced frequency are supplied to a
`multistate counter 56. Selected outputs of counter 56
`provide addresses to the address inputs of a ROM
`(PROM) 58. ROM 58 is preferably a non volatile, non
`alterable ROM which has portions of the ID code
`burned in at sequential addresses thereof. The parallel
`outputs of counter 56 thus address sequential locations
`of the ROM so that the ID code is read out in parallel
`data format to a MUX 60. MUX 60 performs the func-
`tion of serializing the parallel format data containing the
`ID code for presentation to the modem 46.
`Turning now to FIG. 4, there is illustrated another
`embodiment of a tag according to the present invention.
`The tag 24, illustrated in FIG. 4 is “smart” in that it is
`bi-directional and incorporates a local microcomputer
`for purposes which will become apparent hereinafter.
`Tag 24, comprises a code generator 68 that bi-direction-
`ally communicates via a short haul modem 70. Thus,
`code generator 68 communicates serial code data con-
`taining the unique ID code over a line 82 to the transmit
`data (TD) input of modem 70, and modem 70 may com-
`municate serial code data to the code generator 68 (for
`purposes which will become apparent hereinafter) on a
`line 84 from its receive data (RD) output. The ID code
`provided by code generator 68 is modulated by modem
`70, and the modulated data is provided at the transmit
`carrier (TC) output on a line 86 to a transmitter/buffer
`72. Transmitter/buffer 72 impresses the modulated data
`containing the ID code on a line 34’ coupled to the
`power bus 20.
`Tag 24’ may also comprise a receiver/buffer 74 hav-
`ing an input coupled to the line 34, for receiving modu-
`lated data impressed on the power bus 20 by an external
`source, such as by a field programmer 90. Received
`modulated data is provided by receiver/buffer 74 over
`a line 88 to the receive carrier (RC) input of modem 70.
`Modem 70 demodulates the received data and provides
`the same to the code generator 68 via line 84 coupled to
`the receive data (RD) output of modem 70. Control
`lines (not shown) coupled between code generator 68
`and modem 70 provide control signals that control the
`flow of data therebetween in well known manner.
`A power supply 80 receiving input power from the
`power bus 20 supplies power of appropriate voltage to
`each of the code generator 68, modem 70, transmitter/-
`buffer 72 and receiver buffer 74.
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`The code generator 68 of the tag 24, includes the
`earlier referenced local microcomputer, labeled as 78,
`and an electrically alterable ROM such as an EEPROM
`79. EEPROM 79 and microcomputer 78 are coupled in
`well known fashion by means of data and address buses
`and appropriate read/write/enable control lines. The
`ID code is stored in EEPROM 79. The microcomputer
`78 may be suitably programmed to repeatedly and cy-
`clically provide the ID code over line 82 to the modem
`70 for impression upon the bus 20 by means of transmit-
`ter/buffer 72, as in the case of the tag 24 of FIG. 3.
`However, inasmuch as tag 24, is capable of bi-direc-
`tional communication, microcomputer 78 may be suit-
`ably programmed to provide the ID code for impres-
`sion on the power bus 20 only when requested by the
`IFU 26. Thus IFU 26 may request data from the tag 24
`by placing appropriate control
`instructions on the
`power buses 18, 20- for reception by the receiver/buffer
`74 and processing by the microcomputer 78. Thereafter,
`microcomputer 78 may respond to provide the re-
`quested code or other requested data. Well known pol-
`ling or handshaking techniques may also be used for this
`information exchange.
`As mentioned, the tag may be provided with inputs
`for receiving signals from sensors carrying trailer pa-
`rameter data. Tag 24’ may have this capability. As illus-
`trated, microcomputer 78 may have a plurality of inputs
`38 for receiving outputs from trailer sensors. Mi-
`crocomputer 78 may process the trailer parameter data
`in any well known fashion to place the same on the
`power bus 20 for receipt by the IFU 26. For example,
`the trailer parameter data may be repeatedly and cycli-
`cally be placed on the power bus 20 together with the
`ID code. Alternatively, the trailer parameter data may
`be impressed on the power bus 20 only when requested
`by the IFU 26. Still further, trailer parameter data may
`only be impressed on the power bus 20 when mi-
`crocomputer 78 detects an abnormality in one or more
`of those data. In any event, the trailer parameter data is
`modulated by modem 70 and impressed on the power
`bus 20 by transmitter/buffer 72.
`FIG. 4 illustrates a field programmer 90 that may be
`coupled to the power bus 20. Field programmer 90 may
`include any well known field programmer and appro-
`priate circuitry, including a modem, for sending instruc-
`tions to the microcomputer 78. The function of field
`programmer 90 is to alterpand/or verify the ID code
`stored in the EEPROM 79 and/or to alter the mi-
`crocomputer’s operating program. Thus, the operating
`program, or ID code stored in the EEPROM 79 of tag
`24’ may be altered and/or verified by any authorized
`personnel carrying a field programmer 90.
`FIG. 5 illustrates a preferred embodiment of an IFU
`according to the present invention. As illustrated, IFU
`26 preferably comprises a microcomputer 92 having
`ROM and RAM for program storage, scratch pad, etc.
`Microcomputer 92 bi-directionally communicates with
`a DUART (dual universal asynchronous receiver/-
`transmitter) via data lines 104, address lines 106 and
`control lines 108, all coupled in well known manner.
`One-half of DUART 94 communicates with a short
`haul modem 96, while the other half communicates with
`the MST 28 via its RS 232 serial port. As illustrated,
`modem 96 provides demodulated digital data from its
`transmit data (TD) output to the receive data input
`(RXDA) of one half of DUART 94 via line 110. Op-
`tionally, one half of DUART 94 may provide serial data
`at its transmit data output (TXDA) via line 112 to the
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`4,897,642
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`9
`receive data input (RD) of modem 96 for modulating
`the same and impressing it upon the power bus 18 via a
`transmitter/buffer 99, for purposes which will become
`evident hereinafter. The receive carrier input (RC) of
`modem 96 receives modulated digital data over a line
`116 provided by a receiver/buffer 98 coupled to the
`power bus 18 via line 30. If transmit/buffer 99 is pro-
`vided, modulated digital data is provided by modem 96
`at its transmit carrier output (TC) and impressed on the
`power bus 18 via line 30. The half of DUART 94 dedi-
`cated to communicating with modem 96 is coupled
`thereto via control lines 114 connected in well known
`manner.
`
`As illustrated, the other half of DUART 94 commu-
`nicates with the MST 28 by means of a receiver/buffer
`118 connected to its receive data input (RXDB) via a
`line 122 and a transmitter/buffer 120 connected to its
`transmit data output (TXDB) via line 124. Control lines
`126 (for providing the CTS and RTS signals) are also
`coupled between the MST 28 and the DUART 94. As
`mentioned, the signals RXDB, TXDB, CTS and RTS
`are provided to a RS 232 serial port of MST 28.
`A power supply 100 receives input power from the
`power bus 18 and supplies power of appropriate voltage
`levels to receive/buffer 98, modem 96, DUART 94,
`microcomputer 92, and other circuitry as required.
`If desired, a display 102 may be provided and coupled
`to the microcomputer 92 for visually presenting vehicle
`status information, such as the status indication, alarm
`conditions, etc. A printer, or audio means for providing
`voice output, may be provided in substitution for or in
`addition to the display 102.
`As has been