Abstract:
A monitor is disclosed that presents a negligible load to a hardwired interface, provides electrical isolation between all of the interconnected equipment, adds no significant delay to the interface data, provides for maximum reliability of interface operation, provides for remote operation of the monitoring function, provides for noise immune reception of interface data, maintains interface controlled impedance, provides for ease of installation, and does not perturb system operation in any significant way.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America, for governmental purposes, without the payment of any royalty thereof or therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to the monitoring, more particularly, to a monitor having an interface which is hardwired and interposed between first and second digital equipments that exchanges the digital information therebetween and the monitor routes the digital information to means for capturing, recording, and analyzing the routed digital signals. 
     An increasing complexity of computerized systems has created a need for a concomitant developmental engineering evaluation equipment for monitoring computer interfaces, such as the interfaces found in military installations that employ a Naval Tactical Data System (NTDS) protocol. The NTDS protocol comprises a parallel transmission technique conforming to military specifications, such as military standard, input/output interfaces, standard digital data, Navy systems, MIL-Standard-1397C, herein incorporated by reference and which defines and describes the parameters of the Naval Tactical Data System (NTDS) interfaces which are of particular importance to the present invention. Systems which meet the requirements of military specifications are known and one such system is described in U.S. Pat. No. 5,661,583 which is herein incorporated by reference. 
     A monitoring activity may be conducted for such practices as verifying proper computer control of a sensor, developing algorithms for data processing, verifying system performance, and other tasks related to computerized system development, acceptance, or improvement. The physical parameters of the environment in which the monitoring activity is conducted, especially for NTDS interfaces, varies from a relatively benign laboratory setting to the more severe shipborne embedded installations. Similarly, the range of cost factors that accompanies the monitoring activity varies from the relatively inexpensive laboratory testing to the expensive and critical data collection missions aboard a Navy vessel. 
     The monitoring activity typically involves routing digital data under consideration to means for capturing, recording and analyzing the digital data, such as that described in U.S. Pat. No. 5,614,896 which is herein incorporated by reference. This capturing, recording and analyzing means is commonly referred to as an instrumentation system, which terminology is used herein. 
     Various attempts to provide equipment for monitoring the activity for a NTDS interface have been made, but each suffered a shortcoming with respect to disturbing the interface or computerized system under the test. One such attempt involved a so-called “three-way cable tap” which involved the installing of cabling between first digital equipment (generally referred to as a source), second digital equipment (generally referred to as a destination), and the instrumentation system. This technique yielded a common interface between the source, destination and instrumentation systems. Experience has shown that the lack of ground isolation between the source and destination equipment and instrumentation system can disrupt the interface under test. For example, electrical noise undesirably created in the instrumentation system can disadvantageously find its way onto the common interface, and, then, into the source and destination equipment. Other problems with this approach involve distortion of the controlled impedance of the signal carrying conductors of the NTDS interface created by the impedance loading effects of the instrumentation system on the NTDS interface. 
     Another attempt to provide for the monitoring activity for the NTDS interface does not involve any hardwired interface between the involved equipment, but rather is handled by providing a dedicated output channel of the computerized equipment being monitored and analyzed. The dedicated channel provides associated output digital information directly to the instrumentation system. This approach eliminates the grounding and impedance loading problems, but is expensive in that it consumes a data channel of the computerized equipment being analyzed. It is desired that means be provided for routing the data being exchanged over a digital interface between first and second digital equipments to an instrumentation system without causing any impedance loading or ground problems, or any data distortion, while at the same time not consuming a dedicated data channel of either of first or second digital equipment under analysis. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a monitor interposed between first and second digital equipments and routing the information exchanged between the first and second digital equipments to an instrumentation system, without causing any disruption of the digital data and without causing any undesired loading of the instrumentation system onto the interface between the first and second digital equipment. 
     The monitor is interposed between the first and second digital equipments that communicate with each other by digital signals respectively carried by first and second connectors each comprised of conductors. The digital signals is defined and controlled by a first protocol, preferably a NTDS protocol. The monitor comprises joining means, an input stage and an output stage. The joining means has direct-current conductivity to each of the conductors of the first and second connectors so as to form a hardwired interface between the monitor and the first and second digital equipments. The input stage has receiving means connected to the joining means and utilizing logic levels compatible with the first protocol. The receiving means provides output signals. The output stage has optoelectronic devices that receive the output signals of the receiving means and provides output signals serving as the output signals of the monitor. 
     OBJECTS OF THE INVENTION 
     It is a primary object of the present invention to provide a monitor interposed between first and second digital equipments for routing the digital signals being exchanged between the first and second digital equipments to an instrumentation system. 
     It is a further object of the present invention to provide a monitor that does not disturb the system being monitored in function, operation or performance. 
     It is another object of the present invention to provide for a monitor that allows data to be collected which are true representations of the actual computerized system performance being monitored, while at the same time does not compromise the operation of the computerized system being monitored. 
     Another object of the present invention is to provide a monitor that ensures for maximum reliability with respect to continued operation of the computerized system being monitored. 
     Further still, it is an object of the present invention to provide for a monitor that when encountering any failing condition does not affect the operation of the computerized system being monitored. 
     Other objects, advantages and novel features of the invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings therein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram illustrating the monitor of the present invention interposed between first and second digital equipment and providing output signals to an instrumentation system. 
     FIG. 2 illustrates the details of the hardwired interface between the monitor and the first and second digital equipments of FIG.  1 . 
     FIG. 3 is a schematic of the monitor of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, wherein the same reference number indicates the same element throughout, there is shown in FIG. 1 an arrangement  10 , wherein a monitor  12 , which is of primary importance to the present invention, is interposed between first and second digital equipments  14  and  16 , respectively, that communicate with each other by digital signals, and wherein such digital signals are routed to an instrumentation system  18  by way of the monitor  12 . 
     The monitor  12  allows for monitoring activities to be conducted for analysis purposes, verifying proper computer control, developing algorithms for data processing, verifying system performance, and other tasks related to the computerized system made up of either or both of first and second digital equipments  14  and  16  respectively. 
     The first and second digital equipments  14  and  16 , respectively, may form a communication network particularly suited for military installations that employed a first protocol, which may be a NTDS protocol defined by military specification, MIL-Standard-1397C previously mentioned, and which is applicable to Naval Tactical Data System (NTDS) which is of importance to the present invention. The NTDS protocols involve various interfaces, wherein Types A and B NTDS interfaces are of particular importance to the present invention. The first and second digital equipments  14  and  16  are interchangeably referred to herein as NTDS equipments  14  and  16 , respectively. 
     The NTDS equipment  14  may serve as the source/destination digital equipment know in the art, whereas the NTDS equipment  16  may serve as the destination/source equipment, also known in the art. The monitor  12  is connected to NTDS equipment  14  by way of cable  20  having connectors  20 A and  20 B and is connected to NTDS equipment  16  by way of cable  22  having connectors  22 A and  22 B. Furthermore, the monitor  12  is connected to the instrumentation system  18  by way of cable  24  having connectors  24 A and  24 B. The cables  20 ,  22  and  24 , as well as the connectors  20 A,  20 B,  22 A,  22 B,  24 A and  24 B, may be those cables and connectors defined by MIL-Standard-1397C. 
     The instrumentation system  18  serves as the means for capturing/recording/analyzing the digital signals being exchanged between the NTDS equipments  14  and  16 . The instrumentation system may comprise means for capturing and recording a plurality of data transmissions occurring between the NTDS equipments  14  and  16 , and means for analyzing the data transmissions for the developmental engineering purposes or for fault analysis purposes. The instrumentation system receives by way of monitor  12  the digital information shared by the NTDS equipments  14  and  16 . The interconnections of the monitor  12  to the NTDS equipment  14  and  16 , as well as to the instrumentation system  18 , may be further described with reference to FIG.  2 . 
     In general, FIG. 2 illustrates joining means  26  comprised of connectors  20 B and  22 B, cable  32  comprised of individual conductors  32   1  . . .  32   N , connection means  34   1  . . .  34   N , and wires  36   1  . . .  36   N . The connectors  20 B and  22 B are panel mounted connectors mounted on a frame  38  of monitor  12 . The connectors  20 B and  22 B are electrically connected to each other by way of cable  32  respectively carry the digital signals being exchanged between NTDS equipments  14  and  16 , each of which signals is being carried by a respective conductor  32   1  . . . or  32   N . 
     The joining means  26  has direct current conductivity to each of the conductors  32   1  . . .  32   N  by the operation of appropriate means  34   1  . . .  34   N , respectively, such as a crimp tap end, a solder connection or some of similar means. The direct-current conductivity  34   1  . . .  34   N  means provides a hardwired interface between the monitor  12  and each of the NTDS equipments  14  and  16 . More particularly, as seen in FIG. 2, the monitor  12 , and NTDS equipments  14  and  16  share the same common interface, whereby the joining means  26  of the monitor  12  is directly, via appropriate cables and connectors, connected to each of NTDS equipments  14  and  16 . Conversely, as also seen in FIG. 2, the instrumentation system  18  is connected to the monitor  12  via cable  24  and connectors  24 A and  24 B, but has no direct connection to either of the NTDS equipments  14  or  16 . 
     As further seen in FIG. 2, the monitor  12  is connected to the NTDS equipment  14  and  16  in a very reliable manner in that it is essentially connected by means of feedthrough cabling, whose quality of connection is only dependent upon the ability to provide for the direct-current conductivity means  34   1  . . .  34   N . The monitor  12  does not reduce the reliability of the continued operation of the data interchange between digital equipment  14  and  16  as well as does not reduce the reliability of the monitor  12  connection to the equipments  14  and  16 . More particularly, the reliability degradation of the monitor  12  is only dependent on the quality of the connection between NTDS equipments  14  and  16  which, in turn, is only dependent upon the ability to provide for the direct-current conductivity means  32   1  . . .  32   N ; and that there is no dependence upon any active electronics of the monitor  12  for the establishment of this connection. Furthermore, because of the hardwired interface, the monitor  12  does not delay, in any significant manner, the data being exchanged between the NTDS equipments  14  and  16 . Any delay that might be present is due to the internal feedthrough cabling, that is, the length of cabling encompassed by conductors  32   1  . . .  32   N . It is preferred that the wires  36   1  . . .  36   N , which route the data being exchanged between the NTDS equipments  14  and  16  to the monitor  12 , have a length which is less than about 0.5 inches. 
     In general, and as will be further described, the monitor  12  employs bandlimited and low noise electronic components throughout in order to prevent coupling of any noise created by the monitor  12  back onto the digital interface between the NTDS equipments  14  and  16 . The monitor  12  includes the joining means  26  that comprises an impedance match between monitor  12  and connecting cables  20  and  22  so that no distortion or reflection of the digital data interchanged between NTDS equipments  14  and  16  occurs as a result of the interposition of monitor  12 . Furthermore, the monitor  12  provides electronic devices that consume relatively low power from the hardwired interface between the NTDS equipments  14  and  16 , while at the same time provide electrical isolation between the instrumentation system  18  and the NTDS equipments  14  and  16 . The monitor  12  may be further described with reference to FIG.  3 . 
     The monitor  12  comprises an input stage  40  that has a serial arrangement of buffers  42   1  . . .  42   N  and comparators  44   1  . . .  44   N  with a comparator and buffer being provided for each of the wires or conductors  36   1  . . .  36   N  carrying its respective digital signal. The monitor  12  further comprises an output stage  46  comprised of a serial arrangement of optical couplers  48   1  . . .  48   N  and a driver  50   1  . . .  50   N . As seen in FIG. 3, each of the conductors  36   1  . . .  36   N  are provided with separate elements  42 ,  44 ,  48  and  50  so that the monitor  12  is connected in parallel with the NTDS equipments  14  and  16 . 
     The input stage  40  serves as means for receiving digital signals of the interface shared by the NTDS equipments  14  and  16 , is connected to the joining means  26  of FIG. 2 by means of the wires  36   1  . . .  36   N  and utilizes logic levels that are compatible with the first protocol, that is, preferably the NTDS protocol associated with NTDS types A and B interfaces. The input stage  40 , in addition to providing high input impedance that is presented to the NTDS interface between the NTDS equipments  14  and  16  so as not to disturb the impedance match of the joining means  26 , provides output signals that are routed to the optical electronic devices, that is, to the optical couplers  48   1  . . .  48   N  of the output stage  46 . The output stage  46  provides output signals serving as output signals of the monitor  12  which are routed to the instrumentation system  18  by way of the conductors  24   1  . . .  24   N  of cable  24 . 
     The buffers  42   1  . . .  42   N  serve as amplifiers that are used primarily to present a very high impedance between the monitor  12  and the NTDS equipments  14  and  16 , and to isolate the monitor  12  from interacting with the NTDS equipments  14  and  16 . The buffers  42   1  . . .  42   N  provide a negligible system loading by preferably employing junction field effect transistor (JFET) devices which, as known in the art, require negligible input current for their operation. In this way, there is little or no possibility of disrupting the desired operation of NTDS equipment  14  or  16  by the imposition therebetween of the monitor  12  operating to gather and route data to the instrumentation system  18 . 
     The comparators  44   1  . . .  44   N  are preferably those defined and specified by MIL-Standard-1397C and compare threshold levels present at their inputs against the desired specified switching thresholds for the NTDS interface. The use of the comparators  44   1  . . .  44   N , as well as the buffers  42   1  . . .  42   N , prevents low or any noise involved with the operation of the monitor  12  from finding its way to the interface between the NTDS equipments  14  and  16 . Furthermore, unless a match exists between the comparators  44   1  . . .  44   N  threshold levels, the comparators  44   1  . . .  44   N  are not rendered conductive and do not pass digital signals to the respective optical couplers  48   1  . . .  48   N . 
     The optical couplers  48   1  . . .  48   N  receive the information from the comparators  44   1  . . .  44   N  and provide optical electronic isolation for eliminating any electrical conductive connection between the NTDS equipments  14  and  16 , the monitor  12 , and the instrumentation system  18 , each having its own separate electrical ground connection. This freedom of the ground connections between equipments  12 ,  14 ,  16  and  18  eliminates the undesirably normally occurring ground loop currents which, in turn, undesirably provide for potentially disruptive noise that would otherwise be induced back onto the NTDS interface between the NTDS equipments  14  and  16 . 
     The drivers  50   1  . . .  50   N  are preferably NTDS drivers using transistor-transistor-logic (TTL) voltage levels and whose operation are defined by the MIL-Standard-1397C. The drivers  50   1  . . .  50   N  allow for the monitor  12  to be remotely located from the instrumentation system  18  by a relatively large amount, such as that specified in the MIL-Standard-1397C. This feature allows for a convenient placement of the instrumentation system  18  relative to the NTDS equipment  14  and  16 . Furthermore, the drivers  50   1  . . .  50   N  provide a controlled impedance that is presented to the instrumentation system  18  and, thereby prevent any undesired reflections from the instrumentation system  18  from finding its way back onto the NTDS equipments  14  and  16 . 
     The monitor  12  further comprises a fuse  52  having a predetermined prescribed level of rupturing current so as to protect and prevent damage to the monitor  12  during any overload condition. More importantly, the fuse  52 , having connections that are only partially schematically shown, prevents any catastrophic component failure internal of the monitor  12  from creating any damage to the primary equipment, that is, the NTDS equipment  14  and  16 . More particularly, the internal fusing of the monitor  12  prevents any power disruption of the system by the operation of monitor  12 . 
     It should now be appreciated that the practice of the present invention provides for a monitor  12  having an interface which is hardwired and interposed between the NTDS equipments  14  and  16 . The monitor  12  routes the information being exchanged between the NTDS equipments  14  and  16  to the instrumentation system  18 . The monitor  12  employs low power consuming components, while at the same time provides electrical isolation between the NTDS equipments  14  and  16  and the instrumentation system  18 . 
     Obviously, many modifications and variations of the present invention are possible in light of the foregoing teaching. It is, therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.