Patent Publication Number: US-2002004694-A1

Title: Modular automotive diagnostic system

Description:
CROSS REFERENCE TO RELATED APPLICATION  
     [0001] This application claims priority to provisional U.S. application No. 60/067,818, filed Dec. 5, 1997. 
    
    
     
       TECHNICAL FIELD  
       [0002] This invention is within the field of automotive diagnostics and pertains to a modular vehicle diagnostic system. As described below, this invention includes a changeable apparatus for sensing, measuring, calculating, processing, and displaying vehicle data and performance parameters.  
       BACKGROUND OF THE INVENTION  
       [0003] The industry of automotive diagnostics and repair has changed significantly over the last twenty-five years. Vehicles and engines have become more complicated and vehicle performance standards have increased. Consequently, the complexity of vehicle diagnostic equipment has increased. In addition, vehicle parameters that should be tested have increased and continue to change.  
       [0004] The continual improvement of the automobile has created a challenge for diagnostic and repair shops. Much of the diagnostic equipment that is cutting edge today will very likely have to be updated within a few years. In extreme cases, repair shops abandon or sell (usually at a loss) old equipment and obtain new equipment.  
       [0005] Some repair shops contend with the expense of maintaining modern diagnostic and repair equipment by specializing in particular lines of repair. For example, some automotive repair shops perform ignition system diagnostics but do not perform emissions, electronic control module, or other diagnosis. Specializing in one particular line of repair spares the cost and risk of regularly updating an array of other analysis or repair equipment.  
       [0006] Many repair shops that service a variety of vehicle repair needs find that the service equipment takes up a lot of floor space. This may be because some vehicle repair equipment manufacturers prefer to continue to house the equipment in large, floor standing housings. Also, each piece of service equipment may have its own sets of vehicle probes, keyboard, and display screen. Obviously, if more equipment is present, more time and money will be required to keep the equipment functional and more training will be required to keep service people familiar with the different service equipment protocols.  
       [0007] When working with diagnostic equipment, it is desirable to be able to work with the vehicle probes, view the display screen, and input commands quickly and efficiently. It is also desirable to be able to easily move the diagnostic equipment to different service ports within the service station and to move the equipment around a vehicle under inspection, large or small.  
       OBJECTS OF THE INVENTION  
       [0008] It is a general object of the present invention to make a modular vehicle diagnostic system that accommodates the needs of the modern vehicle service technician. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0009] In describing a preferred embodiment of the present invention, reference is made to accompanying drawings, wherein:  
     [0010]FIG. 1 is an illustration showing the possible interconnections between several devices of a modular vehicle diagnostic system according to the present invention.  
     [0011]FIG. 2 is an illustration showing the relationships between modular vehicle diagnostic system devices of the preferred embodiment.  
     [0012] FIG is a detailed illustration of the user interface unit of FIG. 2.  
     [0013]FIG. 4 is a detailed illustration of the diagnostics module of FIG. 2.  
     [0014]FIG. 5 shows a schematic of a ground check test circuit that is part of another aspect of the present invention.  
     [0015]FIG. 6 is a detailed illustration of the scan module of FIG. 2.  
     [0016]FIG. 7 is an illustration of the preferred data cable and one interchangeable test adapter for interconnecting the scan module of the preferred embodiment to vehicle&#39;s communication link connector.  
     [0017]FIG. 8 is an illustration showing the preferred connection of the data cable of FIG. 7 to the scan module.  
     [0018] FIGS.  9  is a detailed illustration of the amplification module of FIG. 2.  
     [0019]FIG. 10 is a block diagram showing the flow of selected signals from the vehicle computer through the break-out box of FIG. 2.  
     [0020]FIG. 11 is a illustration of the 80 to 4 multiplexer of FIG. 10.  
     [0021]FIG. 12 is a detailed illustration of the ignition signal receiver of FIG. 2.  
     [0022]FIG. 13 is a block diagram of the gas analysis module of FIG. 2.  
     [0023]FIG. 14 is a detailed illustration of the docking station of FIG. 2.  
     [0024]FIG. 15 is a partial flowchart of the preferred serial communications protocol for the modular vehicle diagnostic system of FIG. 2.  
     [0025]FIG. 16 is a partial flowchart of the preferred serial communications protocol for the modular vehicle diagnostic system of FIG. 2.  
     [0026]FIG. 17 is a partial flowchart of the preferred serial communications protocol for the modular vehicle diagnostic system of FIG. 2.  
     [0027]FIG. 18 is a drawing showing the bay structure included in the preferred housing assembly for the user interface unit of FIG. 2.  
     [0028]FIG. 19 is a drawing showing further aspects of the housing assembly shown in FIG. 18.  
     [0029]FIG. 20 is a drawing showing the conjoining relation between the user interface unit housing and the housings for the diagnostics and scan tool modules of FIG. 2.  
     [0030]FIG. 21 is a drawing showing the preferred housing assembly for the diagnostics and scan tool modules of FIG. 2.  
     [0031]FIG. 22 is a drawing further showing the conjoining relation between the user interface unit housing and the housings for the diagnostics and scan tool modules of FIG. 2.  
     [0032]FIG. 23 is a drawing showing tabs and latches of the scan tool module housing and the diagnostics module housing of the preferred embodiment.  
     [0033]FIG. 24 is a drawing showing the housings of FIG. 23 in a locked position.  
     [0034]FIG. 25 is a drawing of the housing for the amplification unit of FIG. 2 conjoined to the user interface unit housing.  
     [0035]FIG. 26 is an drawing of the conjoining mechanism of the user interface unit housing of FIG. 25.  
     [0036]FIG. 27 is a drawing showing a communication channel interconnecting a data processor to the user interface unit of FIG. 2.  
     [0037]FIG. 28 is a drawing showing several communication channels illustrated in FIG. 2.  
     [0038]FIG. 29 is a drawing of an assembly that includes a user interface unit and a diagnostic module.  
     [0039]FIG. 30 shows the conjoining features of the user interface unit housing of the preferred embodiment.  
     [0040]FIG. 31 shows the conjoining features of the diagnostic and scan module housings of the preferred embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0041] This invention pertains to modular vehicle diagnostic systems for sensing or receiving selected signals from a vehicle, for selecting vehicle parameters for vehicle diagnosis or evaluation, for accordingly processing the signals, and for displaying the vehicle parameters.  
     [0042] The modular vehicle diagnostic system has a plurality of constituent diagnostic and/or signal processing devices that may be selectively combined to form a vehicle diagnostic assembly. A device may be associated with vehicle diagnosis or performance evaluation or may be associated with some other facet of signal processing and/or interfacing. Two or more devices may be interconnected to produce a single-function or multi-functional vehicle diagnostic assembly unit.  
     [0043] The constituent data processing and diagnostic devices of the modular system may be selectively interconnected to compose a singular vehicle diagnostic assembly unit. Diagnostic assembly units may perform vehicle testing, signal processing, data interfacing and/or other functions.  
     [0044] Diagnostic assembly units may receive signals from a vehicle, process the signals, and/or generate vehicle performance data. Performance data may correspond to ignition system diagnosis, electronic control module (ECM) analysis, emissions or exhaust gas analysis, electrical ground quality, selective component performance evaluations and/or other vehicle operations, systems or components.  
     [0045] Diagnostic assembly units may receive, generate, and transmit vehicle signals for performing signal processing functions including signal multiplexing, artificial signal generating, and vehicle signal modulating.  
     [0046] Diagnostic assembly units may perform data interface functions such as provide a display of vehicle parameters or signal waveforms, receive input from a user, and transfer data to and from external processors or memory storage devices.  
     [0047] Two or more constituent devices may be interconnected by conjoining integral parts of the devices, such as the housings, and/or by providing or establishing one or more electronic communication channel(s) between the devices.  
     [0048] The constituent devices may be conjoined a number of ways. It is preferred that the devices are conjoined with interlocking mechanisms of the type that are at least partially securable to prevent the devices from separating under normal use. For example, in a handheld system, such a secure interlock would allow the operator to grasp any part of an assembly unit and thereby obtain control of all of the interlocked devices. The devices may be conjoined by mating, joining, locking, linking, binding, clasping, or through some other connecting mechanism or technique. For example, the devices may include complementary channels for mating and rotary locking latches, slot and tab assemblies, or Velcro™ strips affixed to the housings. While the above examples provide interlocks that may be relatively easily disengaged, the devices may be conjoined through other means such as screws or nut and bolt assemblies. It should be understood that more than one mechanism may be employed to conjoin devices within an assembly as explained in more detail below.  
     [0049] An interconnection may also be established by providing communication channels between two or more devices. Communication channels may be established in conjunction with, separate from, or exclusive of the conjoining mechanism.  
     [0050] Communication channels allow digital and analog signals to be input to and output from the devices. Digital and analog signals may correspond to data, control, or other information. The devices may transmit and receive automotive-type signals. Automotive-type signals may originate from a vehicle, a memory device, or may be fabricated within the system, with or without input from an operator.  
     [0051] More specifically, a block diagram of a modular vehicle diagnostic system  10  is shown in FIG. 1 and includes several devices  14 ,  16 ,  18 , and  20  that may be interconnected by being conjoined together and/or through a communication channel.  
     [0052] The devices of the modular vehicle diagnostic system  10  may be selectively interconnected. Either one or several of the devices  12 - 20  and/or other devices, not shown, may be interconnected to compose an assembly or a device for testing or evaluating vehicle performance. Consequently, each individual device  12 - 20  may support one or more application(s) for a vehicle diagnostic/evaluation system. For example, the devices within the diagnostic system may include a user interface unit, vehicle signal and data interfacing modules, vehicle signal and data preconditioning modules, and auxiliary components.  
     [0053] A user interface unit may perform one or several universal functions, e.g., displaying test results to an operator on a display and/or receiving input data or information. Consequently, a user interface unit may have application in a majority of diagnostic system applications.  
     [0054] Vehicle signal and data interfacing modules may be provided for performing one or several diagnostic functions, e.g., sensing analog signals from a vehicle and providing an indication of the magnitude of the signals. Such modules may have other applications, e.g., reading data from the vehicle&#39;s computer. Interfacing modules may be dedicated to one or several other functions. One, several, or many interfacing modules may be included in the modular vehicle diagnostic system.  
     [0055] Vehicle signal and data preconditioning modules may be provided for performing one or several signal processing functions, e.g., enhancing signals for input to a vehicle component or module vehicle diagnostic system device. Like the interfacing modules, preconditioning modules may have multiple applications. Several preconditioning modules may be included in an assembly unit.  
     [0056] Auxiliary components may be provided for performing other functions. For example, an auxiliary component may be dedicated to analyzing a vehicle&#39;s exhaust gas concentrations. One or several auxiliary components may be included in an assembly unit.  
     [0057] It should be understood that the requisite devices for performing vehicle diagnosis or evaluation is dependent upon the type of diagnosis or evaluation performed and the functionality provided by the devices within the modular vehicle diagnostic system.  
     [0058] Returning to FIG. 1, devices  14 - 20  may interconnect to  12  as shown. Other configurations are possible. For example, device  16  may interconnect to device  18  only or devices  16  and  18  may each be configured to interconnect to device  12  at a single location, so that only one may be interconnected to device  12  at a time.  
     [0059] It is contemplated that different vehicle tests may be performed by various combinations of the devices of FIG. 1. For example, the combination formed by interconnecting devices  12  and  18  may provide an exhaust gas analyzer for providing a display of the concentrations of particular gases present in the exhaust. Alternatively, interconnecting devices  12  and  14  may provide a system for testing the ignition system. As discussed below, further combinations provide assemblies that may test other systems or components of a vehicle.  
     [0060] As illustrated in FIG. 1, the devices of the preferred embodiment are configured to facilitate interconnection. The devices may include reciprocating structure, as illustrated by tabs  30  and  34  and slots  28  and  32 , for conjoining the housings of two or more devices. The devices may also be interconnected through communication channels.  
     [0061] Exclusive communication channels may be provided for establishing a signal path between two devices if the devices are otherwise not interconnected. For example, exclusive communication channel  42  may be used to transfer diagnostic data from a memory device within device  12  to memory within device  20 .  
     [0062] Preferably, integrated communication channels are associated with the interlocking mechanisms of two or more devices. For example, an integrated communication channel is established between device  12  and device  14  when pins  26  contact slots  24  when tab  30  engages slot  28 . Integrated communication channels are preferable if the transfer of large quantities of data between two devices must be fast and/or bidirectional. An integrated communication channel may support a parallel data port without unduly increasing the size or complexity of the system.  
     [0063] Separate communication channels may be provided between two devices if the devices are not otherwise interlocked or the interlocking mechanism does not provide a suitable structure for incorporating a communication channel. For example, separate communication channel  36  interconnects device  14  and device  16 , although these devices, while conjoined to other devices within the system, are not conjoined to one another.  
     [0064] Each device within the modular vehicle diagnostic system may execute functions that are related to vehicle diagnosis and/or signal processing. A device may have a local control system, i.e., all of the hardware and/or software for controlling the device is within the device, or may receive control commands or a control program from another module or device.  
     [0065] FIG  2  shows, in block diagram form, the preferred embodiment for the modular vehicle diagnostic system of the present invention. The block units represent the devices that may be selectively interconnected. The arrows represent electronic communication channels that may be selectively established. The devices may be conjoined to the same devices with which communication channels are shared or may be conjoined according to some other organizational structure. Conjoining mechanisms are not illustrated in FIG. 2. In the preferred embodiment, selected devices conjoin to the user interface unit  48 . In addition, some selected devices, while sharing communication channels, do not conjoin to vehicle diagnostic system devices.  
     [0066] In general, the devices of FIG. 2 include a user interface unit  48 , vehicle signal and data interfacing modules  50  and  52 , vehicle signal and data preconditioning modules  54 ,  56 , and  64 , and auxiliary components  58 ,  60 , and  62  that may be selectively combined.  
     [0067] A user interface unit  48  may have a data processor, display, operator input components, and communication ports for inputting and outputting data and operating commands to and from devices within the system and/or other devices. The user interface unit may have a housing that facilitates selective interconnection to system devices.  
     [0068] Vehicle signal and data interfacing modules  50  and  52  may input and output operating commands, data, and signals. Accordingly, the interfacing modules may transfer data and signals between vehicle format and user interface unit format and may also include preprogrammed memory. An interfacing module may also include a data processor for calculating vehicle performance parameters or performing other functions.  
     [0069] Vehicle signal and data preconditioning modules  54 ,  56 , and  64  may process signals between a vehicle and vehicle signal and data interfacing modules. The preconditioning modules may process data and signals between forms suitable for vehicle or vehicle components and forms suitable for vehicle signal and data interface modules as explained more fully below.  
     [0070] Auxiliary components  58 ,  60 , and  62  may include devices such as digital processors, microprocessors, signal generators, and memory components for transferring, storing, and/or processing diagnostic data and/or control signals from/to the user interface unit, system devices, or vehicle.  
     The User Interface  
     [0071] The user interface unit may include a display for displaying vehicle parameters and other information. Displayed information may also include instructions on how to interconnect devices or connect probes to the system, an interactive menu for selecting tests to be performed by the diagnostic assembly and selecting other preferences, such as the preferred display format. Additional information may include the condition or status of components within the system and operator information. For example, the display could request a user id-code from the operator. The display may be a liquid crystal display, cathode ray tube, one or more light emitting diodes, or some other device suitable for communicating information to an operator.  
     [0072] The user interface may also include a device for inputting information. Input information may include the selection of tests to be performed, operating commands, a user-id, format preferences, vehicle information, and other data or commands. An input device may include a touch screen, a keyboard or keypad, up/down buttons, a magnetic signal reader, voice recognition, or other device suitable for receiving operator input.  
     [0073] The user interface may also include a data processor. A data processor may control operation of the user interface unit and/or may control some or all of the interconnected devices. The data processor may include memory for storing or displaying vehicle test data and/or other vehicle information. The data processor may also include memory for storing diagnostic system operation software.  
     [0074] A block diagram of the user interface unit  48  of the preferred embodiment is shown in FIG. 3. User interface unit  48  includes a central processing unit  106  for executing user interface and vehicle diagnostic functions. Central processing unit  106  is interconnected to bus driver  116 , bus module interface  142 , PCMCIA card slot  140 , DRAM memory  122 , LCD display RAM  120 , keyboard control  108 , system address decode &amp; power control  130 , and power switch  132 . In the preferred embodiment, bus driver  116  is an RS 232  driver and module interface  142  is an ISA module interface. Power switch  132  controls PCMCIA power control unit  124  and has a manufacturers part number TPS2201.  
     [0075] Central processing unit  106  is also interconnected to LCD  102  and touch screen interface  100 . LCD  102  displays information in alphanumerical and graphical display formats. Information may be input to the modular vehicle diagnostic system through touch screen interface  100 .  
     [0076] Central processing unit  106  is also interconnected to PCMCIA power control  124 , data and address bus buffers  128 , and voltage regulator  110 . Voltage regulator  110  is supplied by main power supply  112  under the control of power control logic  114 . In the presently preferred embodiment, user interface unit  48  receives power from the vehicle battery via the vehicle&#39;s cigarette lighter. The user interface unit may also receive power from a device that receives power from the vehicle battery or from an AC power supply through a DC adapter. User interface unit  48  may also include a battery pack. Batteries may provide operating power and/or backup power during testing.  
     [0077] In the present embodiment, memory device  126  is a basic input/output system (BIOS) and communicates with CPU  106  through buffer data address  128  and system address decode &amp; power control  130 . BIOS  126  may include a ROM and/or flash memory chip.  
     [0078] The user interface unit may include other components for vehicle diagnosis. In an alternate embodiment, the user interface unit includes ports for directly receiving vehicle signal scope lead input signals.  
     [0079] The vehicle signal and data interfacing modules may include a diagnostics module and a scan module.  
     [0080] Returning to FIG. 2, diagnostics module  50  inputs analog signals from vehicle  22 , processes the signals, and outputs digital data to user interface unit  48 . Diagnostics module  50  may also provide signals to vehicle  22  or to other devices within the modular vehicle diagnostic system.  
     [0081] Assuming the devices are interconnected as illustrated in FIG. 2, scope probes and leads  66  sense and transmit analog vehicle signals to diagnostics module  50 . Diagnostics module  50  may also receive conditioned analog vehicle signals from amplification unit  54  or programmable break-out box  56 . Diagnostics module  50  processes and converts the analog signals to digital data. The digital data may be output through bus  80  to user interface unit  48 . Diagnostics module  50  may also output analog signals to amplification unit  54  or directly to vehicle  22 .  
     A Diagnostics Module  
     [0082] The diagnostics module  50  of the preferred embodiment is shown in FIG. 4. Diagnostic module  50  includes digital signal processor  144  interconnected via digital data communication channel  208  to shared memory device  158  and via digital data communication channel  200  to digital multimeter (DMM) circuitry  162  and DAC multiplying/attenuating circuit  152 . Digital signal processor  144  is interconnected via digital data channel  220  and digital control channel  222  to control logic  146 .  
     [0083] Control logic  146  is interconnected to DMM circuitry  162 , 4-channel multiplexer  150 , digital to analog converter (DAC) multiplying/attenuating circuit  152 , analog attenuation circuit  154 , first-in-first-out memory  156 , and shared memory device  158  via digital control channels  206 ,  224 , and  226 , as shown. Analog attenuation circuit  154  receives signals from vehicle  32  via four scope lead input channels  166 ,  168 ,  170 , and  172 , designated yellow, green, blue, and red. Vehicle signals are also provided to DMM circuitry  162 . Analog attenuation circuit  154  provides analog vehicle signals to DAC multiplying/attenuating circuit  152 . Multiplying/attenuating circuit  152  provides vehicle analog signals to output amplification circuit  164  and 4-channel multiplexer  150 . 4-channel multiplexer  150  provides vehicle signals to analog-to-digital converter  148 . Signal generator voltage reference  176  provides a reference voltage to input channels  170  and  172 . In the preferred embodiment, signal generator voltage reference  176  provides +1.2 volts. Ground check circuit  174  may receive battery terminal signals and signals from ground check lead  218 . Ground check circuit  174  provides differential voltage signals to input channel  166  and ground voltage signal to input channel  168 . Output amplification circuit  164  may provide simulated vehicle signals to vehicle  32 . The remaining components may be interconnected as shown in FIG. 4.  
     [0084] As shown in FIG. 2, user interface unit  48  and diagnostics module  50  may be interconnected via bus  80 . Returning to FIGS. 3 and 4, user interface unit  48  and diagnostics module  50  communicate via module interface  142  and base unit interface  230 .  
     [0085] A vehicle diagnostic assembly including user interface unit  48  and diagnostics module  50  may perform a variety of data processing and vehicle diagnostic functions. Vehicle diagnostic functions may include displaying the magnitudes or frequencies of input signals, measuring resistance, and/or functioning as a digital multi-meter or signal generator.  
     Diagnostic Processing Modes  
     [0086] In the present embodiment, the diagnostic module  50 —user interface unit  48  assembly may operate to provide a display of an input signal from any one of the four input channels  166 - 172 . In the present embodiment, data may be processed in either one of two modes, (1) normal and (2) FIFO (first-in, first-out). In normal operation mode, an analog signal is digitized and temporarily stored in memory, where it may be accessed by the user interface unit for display. In the FIFO mode, an analog signal is digitized and processed to a register where the data may be accessed by the user interface for display. The FIFO mode is more suitable if a period or segment of an analog signal is digitized to a relatively large number of data points. In an alternate mode, data may be stored in memory and processed to the FIFO register for access by the user interface unit or other module.  
     [0087] If an operator selects the normal mode of operation, firmware from the user interface unit  48  is downloaded to digital signal processor (DSP)  144 . Diagnostics module  50  is configured to operate in the normal mode via digital control by the user interface unit  48 .  
     [0088] In the normal mode of the present embodiment, analog signals from the input channels are processed to A/D converter  148  via analog attenuation circuit  154  and multiplying/attenuating DAC circuit  152 . Digital signals are processed from A/D converter  148  to control logic circuit  146 . Digital data is processed in control logic  146  to provide data that is suitable for alphanumeric or graphical display. Control logic  146  outputs data to DSP  144 . DSP  144  outputs data to shared memory  158  wherein the data is accessed by the base unit for display on LCD  102 . In the preferred embodiment, DSP  144  may process either scope data (i.e., process the digital data samples and output data in a form suitable for a graphical display), or meter data (i.e., calculate average voltage, RMS voltage, frequency, duty cycle, and pulse width), dependent upon the format selected by the operator.  
     [0089] A second mode of operation, referred to as FIFO data mode, is suitable for collecting high concentrations of data. In the FIFO mode, analog signals from the input channels are processed to A/D converter  148  via analog attenuation circuit  154  and multiplying/attenuating DAC circuit  152 . Digital signals are processed from A/D converter  148  to FIFO memory  156 . Data from FIFO memory  156  may be output directly to user interface unit  48  display. If required by a particular application, data may also be processed by DSP  144  and output to shared memory  158 .  
     Ground Check  
     [0090] In the present embodiment, the assembly formed by conjoining diagnostic module  50  with user interface unit  48  preferably also operates to provide a display of measurements of the resistance of a vehicle ground circuit. Referring to FIG. 4, diagnostics module  50  is shown to include ground check circuit  174 . Ground check circuit  174  may provide up to 250 mA of current for testing the integrity of a ground path.  
     [0091]FIG. 5 shows a block diagram of ground check circuit  174  including vehicle battery  232 . The loaded ground test of the present embodiment measures the quality of the ground path from a component to the negative terminal of battery  232 . In the test, a fixed amount of current is provided to the vehicle electrical system at the point being tested. Using the vehicle battery as a current source, the ground check circuit may simulate operating conditions by providing up to 250 mA of current through a vehicle component.  
     [0092] The positive terminal of vehicle battery  232  provides current for ground check circuit  174 . Current from vehicle battery  232  is routed through known resistance  236  and to the vehicle at the test point. Differential amp  238  provides a differential voltage V 3 , as a function of the drop in voltage from V 1  to V 2 . The voltage levels at V 3  and V 2  are provided to scope lead input channels  166  and  168 , respectively. A/D converter  148  digitizes the voltages. User interface unit  48  further processes the ground check data according to the following formula: 
     R 2 =(V 2 /V 3 )×R 1   
     [0093] User interface unit  48  may display the resistance of the ground path to the negative terminal of the battery, thus providing a check of the integrity of the ground circuit under test.  
     Other Functions of the Assembly  
     [0094] The assembly formed by conjoining diagnostic module  50  with user interface unit  48  preferably also functions as a digital multi-meter (DMM) for measuring resistance, current, and DC and AC voltages. In the DMM mode, scope input lead  184  senses electrical signals from vehicle  22 . The sensed signals are received by DMM circuitry  162  from analog signals channel  188 . DMM circuitry  162  is controlled by control logic  146  and provides to digital signal processor  144  digital data that corresponds to the analog signals from vehicle  22 . Digital signal processor  144  processes the digital data to shared memory  158  for access by the user interface unit  48 . The base unit displays DMM parameters, including DC voltage, RMS voltage, resistance and current.  
     [0095] The assembly formed by conjoining diagnostic module  50  with user interface unit  48  preferably also functions as a signal generator for simulating vehicle signals. Signals generated by the assembly may be substituted for actual vehicle signals and may be displayed on display  102 . At the same time, signals from vehicle sensors, actuators, and/or other vehicle components may be sensed and displayed on display  102 . A mechanic may examine the response of a vehicle component under test to a simulated good or bad input signal.  
     [0096] In the signal generator mode, a digitized waveform is output from user interface unit  48  to shared memory  158 . The digitized waveform may be read from a personal computer memory card inserted into personal computer memory card drive  140  or may originate at the user interface unit under control of an operator. The user interface unit may be programmed to receive waveform parameters via touch screen  100 . The user interface unit may generate one or several periods of the digital waveform to shared memory  158  via module interface  142 . A digitized waveform read from a memory card may also be modified by an operator through commands entered on the touch screen.  
     [0097] A digital waveform entered into shared memory  158  may be read by DSP  144 . DSP  144  outputs the digital waveform data to multiplying/attenuating DAC  152 . DAC  152  outputs the simulated analog waveform to output amplification circuit  164 . The simulated waveform may be amplified or modulated and provided to a component of vehicle  10  via signal generator output leads  212  and  214 . The simulated waveform may be provided to an actuator, sensor or some other vehicle component while the digitized version of the waveform may be displayed on display  102 .  
     [0098] As simulated analog signals are output through leads  212  and  214 , vehicle signals may be sensed by input leads  178 - 184  and processed by diagnostics module  50  to shared memory  158 . Operating under the control of DSP  144 , multiplying/attenuating DAC  152  may both receive analog signals from analog attenuation circuit  154  and provide an analog signal to output amplification circuit  164 .  
     [0099] An alternate method for displaying simulated signals on display  102  includes outputting the simulated signals from output amplification circuit  164  and simultaneously sensing the signals at input channels. The signals may be processed to user interface unit  48  for display on LCD display  68 , as described above.  
     The Scan Module  
     [0100] Interfacing modules may also include a scan module. A user interface unit  48 —scan module  52  assembly communicates with the vehicle via the vehicle&#39;s on-board data communication link connector and displays collected information regarding vehicle systems, including engine control, automatic breaking, cruise control, electronic ride control, and transmission control systems. The scan assembly may allow an operator to retrieve trouble codes, run tests, record data, and display information in text, chart, or graphic format.  
     [0101] The scan assembly may receive vehicle information from vehicle data communication links and may thereby monitor sensor, switch and actuator inputs and outputs, run tests, including road tests, and receive and record trouble codes, data lists, component parameters, and control module information.  
     [0102] Scan module  52  may further provide access to vehicle data lists for display of both discrete (e.g., on/off, open/closed) and analog (e.g., magnitude) parameters. The parameters may correspond to input and/or output programmable control module signals. For example, control module data parameters may correspond to engine speed, brake switches, fuel metering, throttle position, engine and engine coolant temperature, barometric and manifold pressure, air temperature, airflow rate, battery voltage, fuel pump relay voltage, spark timing, emissions, transmission and cruise control, and heating, ventilation, and air conditioning systems.  
     [0103] The assembly formed by interconnecting the scan module preferably includes touch screen  100  on the user interface unit  48  (see FIG. 3) for inputting information such as the identity or make of the vehicle, the vehicle system to be tested, and preferred or selected display formats. The scan assembly also includes LCD display  102  for displaying scan test information and other information such as identifying the correct vehicle test adapter and/or providing instructions of how to connect the scanner to the vehicle.  
     [0104] Turning to FIG. 2, therein is shown scan module  52  in communication with bus  80  and interconnected to vehicle  22  via communications channel  84 . In the present embodiment, communications channel  84  is a serial communications channel.  
     [0105] A block diagram of scan module  52  is shown in FIG. 6. Scan module  52  communicates with user interface unit  48  via serial port  278  and module interface  142 . Serial port  278  is interconnected to serial data channel  280  and data bus and control signal channel  282 . Serial data channel  280  is interconnected to microcontroller  274 . Microcontroller  274  communicates with programmable logic device  284  via address bus  286  and data bus and control signal channel  288 . Microcontroller  274  also communicates with 16-bit transceiver  294  and static RAM devices  290  and  292  via address data bus and control signal channel  288 .  
     [0106] Microcontroller  274  controls the overall operation of scan module  52 . Programmable logic  284  and programmable logic  318  provide control logic, address decode and other control signals. 16-bit transceiver  294  communicates with serial port  278  and module interface  300  via data bus and control signal channel  282 . Programmable logic device  284  transmits memory address data to static RAM  290  and  292  via address bus  296 .  
     [0107] Microcontroller  276  implements all of the vehicle-specific serial communication protocols established by the different vehicle manufacturers.  
     [0108] In the presently-preferred embodiment, software for the scan assembly is stored on memory cards. A first memory card may contain all the scan module program software and support for generic and enhanced OBD-II engine control tests. The first card may also contain tests for electronic systems such as ABS, cruise control, electronic ride control, and transmission control. A second memory card may contain engine control system tests for American and foreign vehicles, and tests for other electronic systems on late model vehicles which may also include ABS, cruise control, electronic ride control, and transmission control. The memory cards are read by user interface unit  48  which downloads the information to the scanner module.  
     [0109] Vehicle interface  316  may include a data cable  240  and an interchangeable test adapter  242 , shown in FIGS. 7 and 8, for facilitating interconnection to a vehicle. An interchangeable test adapter of the present invention may include any one of a plurality of adapters configured to attach to a vehicle&#39;s communication link connector.  
     [0110] Vehicle signal and data preconditioning modules may include an ignition system signal module, an amplification module, and a programmable break-out box module.  
     An Amplification Module  
     [0111] An amplification module may enhance and/or modify modular diagnostic system signals. By enhancing signals, the module vehicle device system widens the range of signal output options for simulating a greater number of vehicle engine control and other signals. An amplification unit may also provide power and ground sources for activating injectors and other devices.  
     [0112] Turning once again to FIG. 2, an amplification unit  54  may receive signals from diagnostic module  50  via analog channel  88 . The amplification unit enhances and/or modifies signals under control of user interface unit  48  via serial communication channel  72 . Processed analog signals may be output to vehicle  22  via scope leads  68 .  
     [0113]FIG. 9 shows a block diagram of the amplification unit  26  for the presently-preferred embodiment. Amplification unit  26  receives signals from diagnostic module  50  at input terminals  344  and  346  and outputs amplified or modified signals at output terminals  352  and  354 . Microcomputer  342  may receive commands from user interface unit  48  at serial interface  340 . Microcomputer  342  may also send status messages to the user interface unit via serial interface  340 .  
     [0114] Amplification unit  54  may have several selectable operation modes. For example, amplification unit  54  may receive and amplify signals through several ranges. For example, in a first mode amplification unit may output a signal having a voltage range of ±6 v and in a second mode may output a signal having a voltage range of ±16 v. In a third mode, power and/or ground sources may be provided for example, to activate selected vehicle components. The amplification unit may include further modes of operation to amplify or modify signals in additional ways, depending upon a desired application. Preferably, an operator may select a desired mode through touch screen interface  100 .  
     [0115] Signals input to amplification unit  54  may include pre-configured signal patterns stored as digital data within the modular vehicle diagnostic system or on a disk or memory card. Input signals may also be programmed or input by an operator or through an external source. The signals may be displayed on LCD display  102  for operator verification or for other purposes. In the preferred embodiment, digital signals (or waveforms) are converted to analog signals by diagnostic module  50 . Analog signals are amplified or modified by amplification unit  54  for input to vehicle  22 . For example, analog signals may be provided by the modular vehicle diagnostic system to drive one or several fuel injectors, activate an automatic breaking system solenoid, or may be provided to a vehicle computer, digital or analog CAM sensor, air temperature sensor, or other device.  
     [0116] Amplification module  54  may include a data processor such as a microprocessor, digital signal processor, or digital controller for controlling or regulating the amplification or modification of signals received.  
     [0117] Referring to FIG. 9, amplification module  54  includes microcomputer  342  for receiving data or information from user interface unit  48  via serial interface  340  and serial driver  116 . The data or information received by microcomputer  342  may pertain to the input signals received at inputs  344  and  346 , amplification or modification parameters, control parameters for configuring the components within the amplification unit, or some additional aspect of signal modification or amplification. Microcomputer  342  outputs configuration or control signals for configuring amplification unit  54 .  
     [0118] In the signal amplification mode, microcomputer  342  receives signals from user interface unit  48  that correspond to the voltage range of the desired amplification module output signal. Microcomputer  342  responsively provides a corresponding reference voltage signal to output lead  356 . Assuming the system is interconnected in a manner consistent with the present description, output lead  356  provides a reference voltage signal to signal generator voltage reference circuit  176  of diagnostics module  50 . In the presently-preferred embodiment, the reference voltage provided by microcomputer  342  corresponds to the desired output signal voltage range as follows:  
                                                   Output signal voltage range   Reference voltage                          ±6 v    .72           ±16 v   .96                      
 
     [0119] Diagnostics module  50  receives from the user interface unit digital data that corresponds to the shape of the desired output signal. The digital data is converted to an analog signal at digital to analog converter  152 . The analog signal is amplified to within a predefined voltage range at output amplification circuit  164 . The predefined voltage range corresponds to the reference voltage at signal generator voltage reference  176  as follows:  
                                                   Reference voltage   Voltage range of output signal                          .72   0-6 v           .96   0-8 v                      
 
     [0120] In addition to providing a reference voltage to the diagnostics module, microcomputer  342  configures amplification module buffer amplifiers  348  and  350  to provide a voltage shift of the signal output by output amplification circuit  164 . Microcomputer  342  also configures power amplifiers  378  and  380  to provide a voltage gain. The voltage shift and voltage gain are dependent upon the parameters of the desired output signal, as follows:  
                                                   Output signal range   Gain Formula                          ±6 v    output = 2*(input − 3)           ±16 v   output = 4*(input − 4)                      
 
     [0121] The signal amplified at power amplifier  380  is output at signal output lead  354 . The signal amplified at power amplifier  378  is provided to relay  382  for selective output to output lead  352 . In signal amplification mode, relay  384 , under control of microcomputer  342 , provides the output of buffer amplifier  348  to power amplifier  378 . In a different mode, described below, relay  384  provides the output of buffer amplifier  348  to decoder logic circuit  386 .  
     [0122] Amplification module  54  may also operate in a driver mode. In the driver mode of the present embodiment, amplification module  54  outputs half-bridge driving signals (i.e., source or sink current waveforms).  
     [0123] Amplification module  54  generates source and/or sink currents through microcomputer control of decoder logic circuit  386 . Decoder logic circuit  386  controls the status of high current drivers  388  and  390  for providing an output signal at output lead  352 .  
     [0124] In the present embodiment, microcomputer  342  configures decoder logic  386  to be responsive to signals provided by diagnostics module  50  and received at amplification module input channel  344 . Decoder logic  386  controls current drivers  388  and  390  to provide the following outputs to relay  382  in response to the voltage received at input channel  344 :  
                                   Voltage from Diagnostics Module   Output Current Source or Sink                  10 V    15 A source       8 V   5 A source       6 V   0 A       4 V   5 A sink       2 V   15 A sink                  
 
     [0125] In the driver mode, microcomputer  342  controls relay  384  to provide an output signal to decoder logic  386  and controls relay  382  to receive an input signal from the high current driver circuit.  
     [0126] It should be clear that, in the present embodiment, the amount of source or sink current provided by the modular vehicle diagnostic system at output  352  is determined by the magnitude of the voltage provided by diagnostics module  50 . The voltage magnitude parameter may be provided by an operator, an external memory device, the diagnostics module, or some other device.  
     [0127] In the driver mode, the modular vehicle diagnostic system may measure and provide a display of the magnitude of the source or sink current. To determine the source current, differential operational amplifier  392  inputs the voltage differential across resistor  396  and outputs the magnitude thereof at output lead  368 . Diagnostic module  50  receives the voltage magnitude, converts the analog magnitude to a digital value and provides the digital value to user interface unit  48 . User interface unit  48  calculates the source current and may provide a display thereof on LCD display  102 .  
     [0128] Similarly, the magnitude of the sink current may be determined by providing the voltage differential across resistor  398  to the user interface unit.  
     [0129] Amplification module output signals may be displayed on LCD display  68 . The “ideal”, or expected, waveform may be displayed by detecting the output of DAC circuit  152 , converting the analog signal to a digital signal, and providing the digital signal to user interface unit  48  for display. The “actual” waveform may be observed by coupling amplification unit input lead  374  or  376  to amplification unit signal output lead  352  or  354 . Amplification unit input leads  374  and  376  are output to diagnostics module  50  at communication channels  366  and  372 , respectively. Diagnostics module  50  may digitize the input signals and provide the signals to user interface unit  48  for display, as described above. Driver mode output waveforms may also be displayed.  
     [0130] In a further aspect of the present invention, the modular vehicle diagnostic system may sense and display the input or output voltage signal from a vehicle component. Amplification unit input leads  374  and  376  may be coupled to a vehicle component lead to sense input or output signals and provide the signals to diagnostic module  50  via leads  366  and  372 , as described above.  
     [0131] In summary, a modular vehicle device assembly that includes an amplification module as described may drive a high powered vehicle component, detect the response of the driven component or of some other component in the vehicle, and display the driving signal and detected response signals on the same display screen. Therefore, a mechanic may methodically analyze an engine by injecting known (good or bad) signals directly to one or more vehicle components. Vehicle components may thereby be tested without being removed.  
     Break-Out Box  
     [0132] In a further aspect of the invention, a programmable break-out box module may be interconnected to a modular vehicle diagnostic assembly. A programmable break-out box module may sense all or several signals at the vehicle computer and output selected signals to other devices for processing, display, or performing diagnostic functions.  
     [0133] In the presently-preferred embodiment, signals between vehicle  22  and vehicle computer  400  are sensed by connectors  402 , as illustrated in FIG. 10. In the present embodiment, the configuration of the connectors is dependent upon the vehicle model. The connectors provide programmable break-out box module  56  a binary code correspondent to the connector configuration and, hence, the vehicle model. As explained below, the programmable break-out box module  56  utilizes the binary code to control operation. Programmable break-out box module  56  receives control signals from user interface unit  48  and provides selected vehicle signals to diagnostic module  50 . While the selected vehicle signals may be either analog or digital vehicle signals, programmable breakout box  56  provides the vehicle signals as analog signals to diagnostic module  50 , where the signals are digitized, processed, and output to user interface unit  48 .  
     [0134] In the presently preferred embodiment, user interface unit  48  provides control signals to programmable break-out box  56  through serial communication channel  72 . Break-out box  56  detects signals at the vehicle computer and provides up to four signals to diagnostic module  50 .  
     [0135] Referring to FIG. 10, therein is illustrated a block diagram of a break-out-box  56  of the present embodiment. Generally speaking, break-out-box  56  is a controllable analog multiplexer with buffered protected inputs and internal voltage dividers.  
     [0136] The signals detected by the connectors  402  are provided to an input circuit  406 . Input circuit  406  protects break-out box module circuitry from excessive vehicle voltage signals. In the presently preferred embodiment, input circuit  406  includes 80 channels, each having a voltage follower and voltage divider circuit. Each channel may process an input signal having a magnitude of up to 50V and is protected to 100V for constant voltage signals and to 300V for short-term voltage spikes. Input circuit  406  also includes 1:12 voltage dividers for scaling down the input voltages.  
     [0137] In the present embodiment, break-out-box  56  functions as a 79-by-4 serially controlled analog multiplexer. An 80-to-4 multiplexer  408  receives input signals from input circuit  406 . Seventy-nine (79) of the inputs are vehicle computer signals and one input is provided by the vehicle battery. Under the control of microcontroller  404 , multiplexer  408  provides up to four input signals to buffer circuit  410 .  
     [0138] As shown in FIG. 11, multiplexer  408  includes seven cross-point switches  412  arranged in three stages. In the first stage, the input signals are provided to five 16-to-4 multiplexers. The outputs of four of the multiplexers are provided to a single 16-to-4 multiplexer in stage two. Stage  3  receives the output of stage  2  and the output of the remaining multiplexer of stage  1 . Microcontroller  404  controls the operation of multiplexer  408  via control channel  414 .  
     [0139] Microcontroller  404  may control multiplexer  408  according to a program stored in memory within microcontroller  404  or received from some other device within the vehicle diagnostic system. Microcontroller  404  may also operate according to control signals received via communication channel  416 .  
     [0140] In the presently-preferred embodiment, user interface unit  48  issues to microcontroller  404  commands via serial interface  72 . Each command is translated by microcontroller  404  into a sequence of control signals so that multiplexer  408  outputs selected vehicle computer signals to buffer circuit  410 .  
     Ignition System Module  
     [0141] In a further aspect of the invention, an ignition system signal module is provided for receiving, conditioning and processing ignition system signals. The ignition system signal module may function as a buffer between a vehicle&#39;s ignition system and the modular vehicle diagnostic system. The ignition system signal module may also adjust ignition system signal magnitudes to within ranges suitable for processing by other devices within the modular vehicle diagnostic system. The ignition system signal module may also output selected ignition signals. The ignition system signal module may perform other functions, such as comparing signal magnitudes, frequencies, or other attributes.  
     [0142] In the presently-preferred embodiment, an ignition signal receiver module may receive selected ignition signals from an ignition lead set  76  and provide selected, conditioned signals to diagnostic module  50 , as illustrated in FIG. 2. Diagnostic module  50  processes the received signals and generates representative signals in digital format therefrom for output to user interface unit  48 , as explained above.  
     [0143] The ignition signal receiver module of the present embodiment may receive a plurality of ignition signals from both conventional and distributorless ignition systems, including primary ignition signals, positive and/or negative secondary signals, number one cylinder signals, battery voltage and current signals, and vacuum and pressure device signals. The ignition signal receiver module processes ignition signals under the control of a microprocessor.  
     [0144] Referring to FIG. 12, ignition signal receiver module  64  may receive distributorless secondary ignition signals at terminals  420 A and  422 A and/or conventional secondary ignition signals at terminals  420 B and  422 B. Primary ignition signals may be received at terminals  424 A and  424 B for conventional and distributorless ignition systems, respectively. Primary and secondary ignition signals may be processed to respective signal interface networks  426 - 436  for conditioning. For example, in the present embodiment, the signal interface networks operate under control of a processor  440  to adjust the primary and secondary input signals to within a 0-6.5 volt range. Spark gap circuit protection components  480 - 490  may be provided to protect the ignition signal receiver module from excessive voltage signals from vehicle  22 .  
     [0145] Microprocessor  440  may control the ignition signal receiver module according to a program stored in memory within microprocessor  440  or received from some other module within the vehicle diagnostic system. In the presently preferred embodiment, microprocessor  440  receives operational software from user-interface unit  48  via a serial communication channel.  
     [0146] Conditioned primary and secondary input signals may be buffered by buffers  442 - 446  and input to analog cross-point switch network  438  for selective output to signal drivers  448 - 454 . Cross-point switch network  438 , switches  442 - 446 , and drivers  448 - 454  operate under control of microprocessor  440 . The ignition signal receiver module outputs selected ignition signals to the modular vehicle diagnostic assembly. In the presently preferred embodiment, the ignition signal receiver module, when interconnected to a modular vehicle diagnostic assembly, outputs selected ignition signals to diagnostics module  50  input leads  178 - 184 .  
     [0147] Ignition signal receiver module  64  may also include an input terminal dedicated to receiving a vehicle&#39;s number-one cylinder ignition signal. A dedicated number-one cylinder ignition terminal allows the modular vehicle diagnostic assembly to identify primary and secondary ignition signals by cylinder number.  
     [0148] The number-one cylinder signal may be received at input terminal  456 , buffered at buffer  458 , and input to analog cross-point switch circuit  438 . Cross-point switch circuit  438  may output a number-one cylinder signal to a signal driver  448 - 454  under control of microprocessor  440 .  
     [0149] Ignition signal receiver module  64  may also include input leads for receiving signals related to vacuum and pressure components of an ignition system. In the present embodiment, input lead  456  may receive signals from a vacuum probe and input lead  470  may receive signals from a pressure probe. Vacuum and pressure input signals processed through signal buffers, analog cross-point switch circuit, and signal divers, are output to the diagnostic module, as described above.  
     [0150] The ignition signal receiver module  64  may also include a current probe for monitoring battery current for testing the performance of vehicle systems such as the cranking and charging systems. In the present embodiment, a current probe detects battery current and outputs a differential voltage to differential amplifier  464 . The differential voltage signal is processed to analog cross-point switch circuit  438  and to output drivers  448 - 454 , as described above.  
     [0151] The ignition signal receiver module  64  may also include battery voltage circuit  474  for monitoring battery voltage and a diode ripple circuit  476  for detecting the effects of the alternator on the battery output voltage.  
     [0152] Battery voltage may be monitored by battery voltage circuit  474  to test the charging system and/or the output of the battery when the ignition switch is engaged.  
     [0153] The diode ripple circuit includes a bandpass filter for filtering out the DC and high frequency components of the battery voltage. The diode ripple circuit  476  provides the filtered battery waveform to analog cross-point switch circuit  438 .  
     [0154] While the ignition signal receiver module of the present invention may be powered by internal or external power supplies, the present embodiment includes a DC-DC converter  478 , as shown in FIG. 12, for powering ignition module components from the vehicle battery.  
     [0155] Auxiliary components of the present invention may include a gas analysis module, a docking station, and/or data processing and display devices.  
     Gas Analysis Module  
     [0156] A gas analysis module may receive vehicle emission gases, measure the amount or concentration of one or several selected gases, and output a signal or signals representative thereof. Referring to FIG. 2, gas analysis module  58  receives samples of vehicle exhaust via exhaust intake hose  82 . Gas analysis module  58  may analyze emission samples, generate data signals, and/or provide signals to other devices within the modular vehicle diagnostic system. The modular vehicle diagnostic system may process the signals and generate data for display or may process the data in conjunction with data received from other tests to provide vehicle performance or condition parameters. Gas analysis module  58  outputs digital data signals representative of exhaust gas concentrations to user interface unit  48  via serial communications channel  70 . Gas analysis module data includes concentrations of hydrocarbons, carbon monoxide, carbon dioxide, oxygen, and oxides of nitrogen. In the present embodiment, gas analysis module  58  is manufactured by Andros (model 6600).  
     [0157] The gas analysis module  58  of the preferred embodiment is shown in FIG. 13. Exhaust samples received from exhaust intake hose  82  are provided to Andros gas analyzer  500 . Sampled gases are discharged through outlet  508 . Andros gas analyzer  500  is in serial communication with Andros board  502  via communication channel  504 . Andros board  502  communicates with the modular vehicle diagnostic system via communication channel  70 . In the preferred embodiment, gas analysis module  58  is in serial communication with user interface unit  48 , as shown in FIG. 2. User interface unit  48  provides control signals to gas analysis module  58 . Gas analysis module  58  responsively generates and outputs exhaust sample data. Exhaust data is processed by the user interface unit for display or vehicle condition or performance evaluation.  
     [0158] Gas analysis module  58  may also provide power to other modular vehicle diagnostic system devices. In the presently-preferred embodiment, the gas analysis module receives power from the vehicle battery. Power for the other devices is provided at power terminal  510 .  
     Data Processing with A Docking Station  
     [0159] Auxiliary components of the present invention may also include a data processing device for functioning with one or several devices within the modular vehicle diagnostic system. For example, a personal computer may communicate with selected devices for performing selected tests and for receiving and displaying diagnostic data and/or inputting control commands.  
     [0160] The data processing device may also perform other functions related to automotive performance evaluation but not associated with the modular vehicle diagnostic system. For example, the data processing device may also interact with other equipment in an automotive repair shop and/or function as a central hub of vehicle diagnosis, sales and inventory.  
     [0161] The data processing device may further perform functions not unique to automotive performance evaluation, such as work processing, accessing remote data bases, and/or driving peripheral devices, such as a printer or sound system.  
     [0162] In furtherance of this aspect of the present invention, a docking station  60  is provided through which a communications link between a data processing device and selected devices within the modular vehicle diagnostic system may be established. In the presently-preferred embodiment, a docking station is provided for converting data and control information between communication formats implemented by the data processing device and communication formats, discussed below, of other vehicle diagnostic system devices.  
     [0163] Turning once again to FIG. 2, therein is shown a docking station  60  in communication with the modular vehicle diagnostic system and data processing device  62 . Data processing device  62  may include a display for displaying menu and control information and diagnostic data associated with the vehicle diagnostic system. Data processing device  62  may also include an input device, such as a keyboard or touch screen display, for inputting operator commands and other information.  
     [0164] Docking station  60  may include several ports for interconnection to various modular devices, including data processor  62 , and may include memory and processing devices for converting between different communication formats, such as bit processing formats.  
     [0165] A block diagram of docking station  60  of the present embodiment is shown in FIG. 14. Docking station  60  includes several ports for interconnecting to different modular vehicle diagnostic system devices for receiving and providing signals in different formats. In the present embodiment, docking station ports have interface circuits associated therewith for adjusting output signals. For example, interface circuits  520 ,  522 ,  542 , and  544  may be level shifters for providing a desired shift in voltage between input and output signals.  
     [0166] Docking station port  520  may receive or provide digital signals transferred serially from/to data processor  62 . Docking station ports  522 ,  542 , and  544  may receive or provide digital signals serially transferred from/to other devices within modular vehicle diagnostic system  10 . In the present embodiment, docking station ports  520 ,  522 ,  542 , and  544  are RS- 232  serial data voltage level shifters. Devices that utilize parallel bit processing may be interconnected to docking station  60  at header  524 .  
     [0167] The docking station  60  of the present embodiment includes a processing unit  526  for translating modular vehicle diagnostic system data between different bit processing formats. In the present embodiment, processing unit  526  translates between parallel and serial bit processing formats. Processing unit  526  is interconnected to data bus  532  and address bus  534 . Data bus  532  and address bus  534  are interconnected to memory devices  528  and  530 . Memory device  530  may provide memory for program storage and non-volatile data storage and memory device  530  may provide memory for use by processing unit  526  for program execution. In the presently preferred embodiment, memory device  528  is a static RAM and memory device  530  is a flash memory chip.  
     [0168] In the presently preferred embodiment, processing unit  526  includes a device for converting input/output signals to desired bit processing formats. In addition, dual UART (DUART)  540  may also, under the control of data processor  526 , convert signals to desired bit processing formats. Both data processor  526  and DUART  540  are connected directly to data bus  532  and address bus  534 , which, in turn, are connected to translator buffer  536  for processing data in parallel format to/from debug header  524  via module bus  538 .  
     [0169] Docking station  60  further includes a logic circuit  546  and display  548  for providing an indication of the state of the device. For example, display  548  may include a series of light emitting diodes and provide a signal when the docking station is converting data.  
     [0170] As illustrated in FIG. 14, docking station  60  further includes a power supply circuit  550  for providing docking station  60  with power. In the presently preferred embodiment, power supply circuit  550  is interconnected to a 12 volt DC external power source at input  554  and provides 5 volt and +/−12 volt voltages to docking station components.  
     [0171] Docking station  60  may further include a reset circuit  552  for providing a reset signal to data processor  526 .  
     [0172] In the preferred embodiment, data processor  526  is an AM186ES microcontroller.  
     [0173] A data processing device may also be interconnected to other devices within the modular vehicle diagnostic system  10 . For example, a desktop PC may be serially linked to one of the modules, such as the user interface unit  48 , for receiving diagnostic data. The diagnostic data may be transmitted to the desktop PC as it is acquired or may be transmitted from memory. The data processing device may utilize, store, process, or further transfer the information.  
     [0174] In the preferred embodiment of the present invention, a data processor  62  may be serially linked directly to the user interface unit  48  via a serial data cable  74 . The serial link allows the transfer of selected diagnostic data, stored as files within the user interface unit  48 , from the user interface unit to the data processor. In the present embodiment, data is transferred in accordance with the modular vehicle diagnostic system serial communications protocol, discussed below. It is preferred that the data processor  62  support the diagnostic functions provided by the other modules, so that diagnostic data may be similarly presented on the user interface unit and the data processor  62  displays.  
     Communication Channels  
     [0175] As described above, the modular vehicle diagnostic system of the present embodiment includes a plurality of devices that may be selectively interconnected. An interconnection, for purposes of the present invention, includes establishing at least one communication channel between a selected device and at least one other device within the modular vehicle diagnostic system. A communication channel may require a solid medium, such as a conductive metal. Data may also be communicated between devices by other modes such as through radio waves or electromagnetic radiation.  
     [0176] As described above, several pairs of devices, if interconnected, communicate serially. Because different devices may be connected to a serial port and selected serial communications may be bi-directional, it is preferred that one serial communications protocol be implemented for all devices that input/output data serially.  
     [0177] In the present embodiment, communications between user interface unit  48  and programmable break-out-box  56 , amplification unit  54 , gas analysis module  58 , and data processor  62  occur via serial communication channels. In keeping with the invention, a universal serial communications protocol for all serial communications is defined, thus simplifying the communications code and providing the user interface unit  48  with a consistent mechanism through which to identify devices.  
     [0178] For purposes of the present discussion, user interface unit  48  is the host when communicating with programmable break-out-box  56 , gas analysis module  58 , or amplification unit  54 . Data processor  62  is the host when communicating serially with any device.  
     [0179] In the preferred serial communications protocol, the host always initiates communications. A flowchart of the handshake protocol for the host is shown in FIGS. 15 and 16. As shown in FIG. 15, if the transmission of a message is not successful, the host will resend the message up to two more times. If three successive attempts are not successful, the host records a communication failure.  
     [0180] As shown in FIG. 16, the host requires an acknowledge message from a target device after transmitting a message. If the acknowledge message is negative, the host will retransmit the message. If the acknowledge is positive, the host waits for a response. If a response is received within a predetermined period of time, the host determines if the checksum byte is valid. If the checksum byte is valid, the message was successfully sent. If the message was not successfully sent, the host may resend the message or record a communication failure, as discussed above.  
     [0181] A flowchart for the handshake protocol for a target is shown in FIG. 17. As shown therein, upon receipt of a message, the target determines if the checksum byte is valid. If checksum is valid, the target transmits a positive acknowledge (ACK) signal, processes the message, and sends a response. Upon receipt of a response message, the host does not send an acknowledgment. However, if checksum is not valid, the target transmits a negative acknowledge (NAK). As discussed above, if the transfer of a message is not successful, the host will resend the message up to two more times. If the target receives a defective message, it waits until the host stops transmitting before sending NAK.  
     [0182] The host and response message structures for the preferred embodiment are as follows:  
                               Host message structure                                                Header:   message size - 2 bytes               target id - 1 byte               opcode - 1 byte               checksum - 1 byte           Message:   Length is opcode specific                      
 
     [0183]                               Response message structure                                                Header:   message size - 2 bytes               target id - 1 byte               status - 1 byte               checksum - 1 byte           Message:   Optional                        
     [0184] The target identification bytes for the preferred embodiment are defined as follows (“$” denotes hexadecimal):  
                               Target id byte                                        $00   Any - all targets respond       $01   programmable break-out-box       $02   amplification unit       $03   computer       $04   slave PAC                  
 
     [0185] The status byte in the preferred embodiment is defined as follows:  
                               Status Byte                                                $00-$0F   Reserved for universal codes           $00   OK           $01   Wrong target id           $02   Invalid opcode           $03   Target has been reset           $04   Invalid parameter           $10-$2F   programmable break-out-box error               codes           $30-$4F   amplification unit error codes           $50-$6F   computer error codes           $70-$8F   slave error codes                      
 
     [0186] The serial communications protocol of the preferred embodiment thus allows bi-directional communication between two selected devices and includes a mechanism that verifies the identification of the device and message. The preferred protocol further allows for an expansion of the modular vehicle diagnostic system to include additional modules.  
     Modularity  
     [0187] As discussed above, the devices of the modular vehicle diagnostic system may be selectively conjoined. One or more mechanisms may be used to conjoin the selected devices. A conjoining mechanism may provide or facilitate a desired feature of the modular vehicle diagnostic system. For example, a mechanism may facilitate the establishment of a hardware communication channel and/or maintain a structural concept. For example, it is desirable that the vehicle diagnostic assemblies of the preferred embodiment be portable and readily operable by a single operator, i.e., handheld.  
     [0188] The several devices of the preferred embodiment are housed separately. User interface unit housing  600  is shown in FIGS. 18 and 19. Housing assembly  600  is of a generally rectangular shape that includes side surface  602  opposite user interface surface  616 . User interface surface  616  includes display and touch screen interface  618 .  
     [0189] Side surface  602 , further illustrated in FIG. 30, has a slot or aperture  604  formed therein. In the present embodiment, aperture  604  includes a left side  606  and a right side  608  and terminates at an open end  610  and closed end  612 . Closed end  612  includes a male electric connector  614 , discussed below, that provides a hardware interface for interconnection to other devices of the modular vehicle diagnostic assembly. Aperture  604  is formed to provide an opening that corresponds to the shape of one or several other modular vehicle diagnostic system devices. For example, in the present embodiment, aperture  604  corresponds to the shape of the housings of diagnostic module  50  and scan tool module  52 .  
     [0190] Turning to FIGS. 20 and 21, therein is shown the shape of the housing  620  for both diagnostic module  50  and scan tool module  52 . Housing assembly  620 , is analogous to a key that includes two portions, as further illustrated in FIG. 31. The first portion may be referred to as mating segment  622  and the second portion may be referred to as the access segment  624 . Mating segment  622  is of a shape complimentary to aperture  604 , discussed above. In the present embodiment, mating segment  622  includes a left side and a right side,  626  and  628 , respectively, having apertures formed therein to complement the ridges formed in sides  606  and  608  of aperture  604 . The width of mating segment  622  is equal to the depth of aperture  604 . The horizontal and vertical lengths of mating segment  622  correspond to the horizontal and vertical lengths of aperture  604 . Mating segment  622  further includes female electronic connector  630 , shaped complementary to male electronic connector  614 , discussed above.  
     [0191] Housing  620  may be conjoined to user interface unit housing  600  by sliding mating segment  622  adjacent to and along the length of aperture  604 . When housing  620  is fully inserted in aperture  604 , female electric connector  630  is in contact with male electric connector  614 , mating segment  622  and side surface  602  form a substantially flat surface, and access segment  624  is accessible atop user interface unit housing  600 , as shown in FIG. 22.  
     [0192] The present embodiment of user interface unit housing  600  includes a pair of rectangular apertures for receipt of a pair of rotating tabs  636  and  638  associated with locking latches  632  and  634  integrated with access segment  624 . When housing  620  is fully inserted into user interface unit housing  600 , manual rotation of tabs  632  and  634  locks housing  620  in the fully inserted position, as shown in FIGS. 22 and 24. In the presently preferred embodiment, locking the latches allows an operator to handle user interface unit  48  and diagnostic module  50  or scan tool module  52  as a single device. Of course, other modular vehicle diagnostic system devices may be conjoined and interconnected as described. Diagnostic module  50  and/or scan tool module  52  may be conjoined and/or interconnected through other mechanisms known in the art.  
     [0193] The devices of the modular vehicle diagnostic system may be conjoined by other mechanisms. Referring to FIG. 25, the amplification housing  640  for the amplification unit  54  is shown in its preferred position as conjoined to user interface unit housing  600 . Housing  620  is also shown conjoined to user interface unit housing  600 , to illustrate the preferred relation of amplification unit  54  to diagnostic module  50  and user interface unit  48 , discussed above.  
     [0194] Amplification housing  640  may be conjoined to other devices within the modular vehicle diagnostic assembly through a number of different mechanisms. As shown in FIG. 26, the preferred mechanism includes a bracket  642  secured to the back of the user interface unit housing  600  securing amplification housing  640  to user interface unit  48 . Bracket  642  includes a slot  644  for receipt of key tabs affixed to the back of amplification housing  640 . The key tabs may be slid into slot  644 . Amplification housing  640  may also include spring loaded nylon balls for exerting a constant force between amplification housing  640  and user interface unit housing  600  when the key tabs are inserted into slot  644 . The force exerted by the spring holds amplification housing  640  in a fixed position relative user interface unit housing  600 .  
     [0195] In the present embodiment, gas analysis module  58  also has a housing with key tabs for insertion in slot  644 , as described above.  
     [0196] As discussed earlier, modular vehicle diagnostic system devices may conjoin through other mechanisms. For example, devices may be conjoined by a threaded stud and nut assembly. One or several threaded studs may be affixed to one or several devices. Corresponding apertures may be associated with other devices. Two or several devices may be conjoined by inserting a stud through an aperture. The devices may be secured together by tightening a nut on the stud.  
     [0197] As illustrated in FIG. 2 and explained in detail above, it may be necessary to establish communication channels between selected devices. The communication channels may, in certain applications, be associated with the conjoining mechanism. For example, as shown above, a parallel communication channel between user interface unit  48  and diagnostic module  50  or scan tool module  52  is established when housing  620  is fully inserted in aperture  604  and female electronic connector  630  contacts male electric connector  614 . Other types of communication channels may be established between devices. For example, a serial communication channel may be established between devices when a housing is inserted into an aperture.  
     [0198] Communication channels may be established through mechanisms not associated with the device housings. As shown in FIG. 2, user interface unit  48  may communicate with data processor  62  via serial communication channel  74 . Data processor  62  may or may not conjoin user interface unit  48 . For example, as shown in FIG. 27, serial data cable  646  may provide the only physical link between data processor  62  and user interface unit  48 . Alternatively, separate communication links may be established between devices that are conjoined. As shown in FIG. 2, user interface unit  48  may communicate with amplification unit  54  via serial communication channel  72  and diagnostic module  50  may communicate with amplification unit  54  via analog channels  88 . Amplification unit  54  may also conjoin user interface unit  48 , as shown in FIG. 25. Turning to FIG. 28, therein is shown interface cable  650  interconnected to amplification unit  54 . Interface cable  650  also includes serial data cable  648  for establishing serial communication channel  72  between user interface unit  48  and amplification unit  54 . Analog channels  88  may be established between diagnostic module  50  and amplification unit  54  via analog cables  652 - 658 .  
     Conclusion  
     [0199] The modular system described herein permits a user to select which modules or devices to conjoin in a plug-in system. The system provides an automotive service professional with all the tools necessary to perform precision fault analysis of sophisticated vehicle components.  
     [0200] As discussed above, the modular vehicle diagnostic system is preferably handheld. A handheld system accords an operator of the device the mobility to easily access different vehicle components while maintaining immediate control of the system. As test results are reviewed, new connections to the vehicle under test may be made. An operator may thereby perform vehicle tests without having to walk away from the vehicle.  
     [0201] To diagnose a vehicle, a mechanic chooses the component or system to be tested and interconnects the modules or devices for performing the desired test. For example, a mechanic that would like a display of the secondary ignition signals of a distributorless ignition system would first conjoin the diagnostics module to the user interface unit. The mechanic would also plug the diagnostic module lead set into the diagnostic module and provide a connection from a power source to the user interface unit. FIG. 29 shows the user interface unit  48  conjoined with the diagnostics module  50  and the lead set  700 . The lead set includes power lead  702  connecting AC power supply adapter  704  to the user interface unit  48 . The AC power supply adapter includes a plug for connection to an AC power supply.  
     [0202] The lead set further includes a ground lead  706  for connection to vehicle ground. Secondary leads  708  and  710  are connected to the diagnostic module  50  channels as shown. After selecting the DIS ignition system display from the touch screen of user interface  48 , the mechanic follows the instructions provided on the display for configuring the diagnostic module  50  and connecting the leads to the vehicle. After the user interface unit is properly configured and the test leads are properly connected, the mechanic is prompted to start the test.  
     [0203] Upon starting the test, the user interface provides a display of DIS signals to the mechanic. The mechanic may select a graphical or digital display of data.  
     [0204] A user interface unit serves as a base unit for various assemblies. Additional modules or devices may be obtained at the discretion of a mechanic. For example, a mechanic dedicated to ignition system repair may obtain or purchase only an ignition signal receiver and a diagnostics module. Additional modules, such as a gas analysis module or a scan tool module, may be obtained if the need or desire to expand the capacity of the diagnostic system arises. Further, if advances in automotive or diagnostic technology render a particular module or device out-of-date, that module or device may be replaced without having to replace other devices or modules, such as the user interface unit.  
     [0205] While the invention has been particularly shown and described with reference to certain preferred embodiments, it will be understood by those skilled in the art that various alterations and modifications in form and in detail may be made therein without departing from the spirit and scope of the invention.