Abstract:
A connector apparatus is adapted for determining cable connection status and comprises a first connector. The first connector comprises a plurality of contacts capable of coupling to a corresponding plurality of conductors in a cable, a substrate supporting the plurality of contacts, and an insulator layer encasing at least a portion of the individual contacts of the plurality of contacts and mutually isolating the contacts. The first connector further comprises a shroud enclosing the plurality of contacts, the substrate, and the insulator layer. The shroud is electrically conductive and separated into first and second electrically isolated segments. Each of the first and second segments is electrically connected to respective first and second reference contacts.

Description:
RELATED APPLICATIONS 
   The disclosed system and operating method are related to subject matter disclosed in the following co-pending patent applications that are incorporated by reference herein in their entirety: (1) U.S. patent application Ser. No. 10/370,358, entitled “High Speed Multiple Port Data Bus Interface Architecture”; (2) U.S. patent application Ser. No. 10/370,414, entitled “High Speed Multiple Ported Bus Interface Control”; (3) U.S. patent application Ser. No. 10/370,361, entitled “High Speed Multiple Ported Bus Interface Expander Control System”; (4) U.S. patent application Ser. No. 10/370,326, entitled “High Speed Multiple Ported Bus Interface Port State Identification System”; (5) U.S. Pat. No. 6,810,439, entitled “System and Method to Monitor Connections to a Device”; and (6) U.S. patent application Ser. No. 10/370,364, entitled “High Speed Multiple Ported Bus Interface Reset Control System.” 

   BACKGROUND OF THE INVENTION 
   A computing system may use an interface to connect to one or more peripheral devices, such as data storage devices, printers, and scanners. The interface typically includes a data communication bus that attaches and allows orderly communication among the devices and the computing system. A system may include one or more communication buses. In many systems a logic chip, known as a bus controller, monitors and manages data transmission between the computing system and the peripheral devices by prioritizing the order and the manner of device control and access to the communication buses. Control rules, also known as communication protocols, are imposed to promote the communication of information between computing systems and peripheral devices. For example, Small Computer System Interface or SCSI (pronounced “scuzzy”) is an interface, widely used in computing systems, such as desktop and mainframe computers, that enables connection of multiple peripheral devices to a computing system. 
   In a desktop computer SCSI enables peripheral devices, such as scanners, CDs, DVDs, and Zip drives, as well as hard drives to be added to one SCSI cable chain. In network servers SCSI connects multiple hard drives in a fault-tolerant cluster configuration in which failure of one drive can be remedied by replacement from the SCSI bus without loss of data while the system remains operational. A fault-tolerant communication system detects faults, such as power interruption or removal or insertion of peripherals, allowing reset of appropriate system components to retransmit any lost data. 
   A SCSI communication bus follows the SCSI communication protocol, generally implemented using a 50 conductor flat ribbon or round bundle cable of characteristic impedance of 100 Ohm. SCSI communication bus includes a bus controller on a single expansion board that plugs into the host computing system. The expansion board is called a Bus Controller Card (BCC), SCSI host adapter, or SCSI controller card. 
   In many systems, a capability to detect attachment of a cable or connector is useful. For example, a system capable of detecting whether a device is attached at the end of a transmission line is useful to supply proper termination impedance to the line. In a specific example, a commonly used parallel input/output (PIO) system for computers, the SCSI protocol interface, requires termination at each end, and only at each end, in a chain of devices. Despite some standardization, many proprietary variations, proposed extensions, and improvements exist that make uncertain the actual configuration of a system. SCSI signal lines may be single ended or differential, either low voltage differential or high voltage differential. Furthermore, a variety of termination alternative exist such as passive termination internal to a device, typically socketed or jumpered for removability, or active termination internal to a device. Other termination alternatives include manually switchable or automatically switchable internal termination, either active or passive, or external termination requiring an additional external connector with termination circuitry plugged into the extra external connector. 
   The multiple connector and termination schemes have led to confusion and the possibility of excessive termination within a device chain. Specifically, a user typically cannot determine from external examination whether a particular device has an internal termination and whether any internal termination is socketed, jumpered, or switched, either active or passive. If a terminator is missing, or a terminator is enabled when improper, the SCSI bus may not function reliably. 
   Plug and Play SCSI standard attempts to simplify connector and termination configurations by specifying one standard connector for external devices and specifying that termination for external devices are external to the devices. Specifically, active external termination is required with terminator power supplied by a designated line in the SCSI bus. Each external device must have two visible external connectors. When external devices are chained, only one connector can remain open and the open connector must receive the one external active termination circuit. This simplification still requires manual intervention, requires a separate part with additional cost, and creates a risk of performance loss if the part is lost. A customer must purchase a separate terminator plug, including active circuitry and a connector, and properly install the terminator plug on the one open external device connector. 
   SUMMARY OF THE INVENTION 
   In accordance with some embodiments of the illustrative system, a connector apparatus is adapted for determining cable connection status and comprises a first connector. The first connector comprises a plurality of contacts capable of coupling to a corresponding plurality of conductors in a cable, a substrate supporting the plurality of contacts, and an insulator layer encasing at least a portion of the individual contacts of the plurality of contacts and mutually isolating the contacts. The first connector further comprises a shroud enclosing the plurality of contacts, the substrate, and the insulator layer. The shroud is electrically conductive and separated into first and second electrically isolated segments. Each of the first and second segments is electrically connected to respective first and second reference contacts. 
   In accordance with other embodiments, a connector apparatus comprises a housing for encasing a plurality of contacts capable of coupling to a corresponding plurality of conductors in a cable. The housing comprises an electrically conductive layer, the electrically conductive layer being separated into mutually isolated segments that are electrically connected upon attachment to a mating connector. 
   In accordance with a further embodiment, a method of detecting connection status comprises encasing a plurality of contacts capable of coupling to a corresponding plurality of conductors in a cable, and conducting electricity along the encasing means, mutually isolating the conducted electricity into two segments. The method further comprises attaching a mating connector to the plurality of contacts and electrically coupling the mutually isolated segments upon the attachment to the mating connector. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the invention relating to both structure and method of operation, may best be understood by referring to the following description and accompanying drawings. 
       FIG. 1  is a schematic block diagram showing an example of a computer system including a bus system. 
       FIGS. 2A and 2B  are schematic pictorial and circuit diagrams that illustrate an embodiment of the disclosed female connector with corresponding male connector not installed and installed, respectively. 
       FIG. 3  is a schematic block diagram showing an example of usage of the illustrative female connector and the manner of operation to enable and disable an active termination circuit. 
       FIG. 4  is a pictorial drawing illustrating another example of a connector that enables detection of a cable connection. 
       FIG. 5  is a schematic block diagram showing an example of a bus architecture that can utilize the illustrative connector to determine whether a cable is connected or unconnected. 
       FIG. 6  is a schematic circuit diagram that can be used to determine whether proper connections are made in the bus architecture shown in FIG.  5 . 
       FIG. 7  is a state diagram showing an embodiment of a state machine capable of determining whether a connector is being attached or removed from the circuit shown in FIG.  6 . 
       FIG. 8  is a state diagram that depicts a state machine embodiment capable of determining whether a connector is properly attached to a device. 
       FIGS. 9A ,  9 B, and  9 C are schematic block diagrams showing examples of bus system configurations that illustrate utility of the disclosed separated connector. 
   

   DETAILED DESCRIPTION 
   Some bus standards, for example the SCSI bus standard, define ends of the bus by bus termination. Bus termination is used to set a negation state when no device is driving, also called biasing, and to match impedance to interconnect media impedance. A termination circuit successfully terminates the bus by complying with specifications for biasing and impedance matching. A termination circuit is termed “enabled” when successfully applying bus termination. Conversely, a termination circuit is “disabled” when not supplying bias and impedance matching functions. A switchable terminator is a terminator capable of being disabled by disconnecting all signal lines, optionally including DIFFSENS, by an electronic switch. 
   What is desired is a system in which a last device in a chain can sense when nothing is plugged into one of the two external connectors and, if so, automatically switches in an internal active termination circuit. 
   One approach to automatic detection of external connector presence is to access a line that is normally grounded by every device on the bus and, for a particular external device, internally pull the line high instead of low. Accordingly, if the line is at ground, an external device is connected. If the line is high, an external device is not connected in a system with all devices connected using the same method. However, SCSI systems may include one or more devices that do not comply with the standard method, so that a high line does not indicate with certainty that the external device is not connected. What is desired is a capability to automatically sense connection of a device with certainty. In some embodiments what is further desired is a capability, in a SCSI system, for automatic connection sensing that is standard for all devices. 
   What is also desired is a general capability, extending beyond the SCSI standard, for automatic detection of the presence of a mating connector. 
   In a two-port bus architecture that specifies a first port with at least one host connection and a second port with another host or terminator connection, a cable sensing connector facilitates algorithms that determine the correctness of the system configuration. 
   Many devices are available in the two-port architecture, for example HP Jamaica drives, HP DS2300, and front ends of HP SC10 Disk System, HP Surestore HVD10, HP DS2100, and other devices and systems, all manufactured and sold by Hewlett-Packard Company of Palo Alto, Calif. Two-port architecture devices are also available from other manufacturers. On-board termination can be added to two-port architectures to simplify user interfaces and reduce overall system cost. 
   A ground pin isolation technique can be used to determine when to activate or deactivate the terminator at each port. A separated connector can be used to determine validity of the overall system configuration. The system configuration is invalid with no termination at the end of the bus. The invalid condition occurs when a cable is added to a system or disconnected from a system in a way that extends the bus past the termination point or disconnects from the termination at the end of the bus. 
   A system can integrate a separated connector that enables the system to sense when an unconnected cable is connected to the system and respond by resetting the bus to avoid data corruption until the configuration is corrected. 
   Referring to  FIG. 9A , a system  900  supports on-board termination and includes termination circuitry TA  902  associated with Port A  904 . Port A  904  is not activated due to a connection to the Host  906  that supplies termination at the end of the bus  908 . On-board termination circuitry TB  912  associated with Port B  914  senses no connection to a Host  906  or external terminator and responds by activating termination. 
   Referring to  FIG. 9B , terminator TE  920  is added to the bus system  900 . Status of termination circuitry TA  902  does not change while termination circuitry TB  912  becomes deactivated by sensing of an external connection from terminator TE  920 . 
   Referring to  FIG. 9C , the bus system  900  is further modified by replacing the terminator  920  with a cable connection  930 . A cable  932  with an unconnected end  934  is connected to Port B  914  so that the bus  908  is improperly terminated since Port B  914  is no longer connected to an external terminator or host. Improper termination is a common consequence when a system is under reconfiguration or troubleshooting. In the illustrative configuration of improper termination, the system  900  with a conventional connector  910  incorrectly continues operating without acknowledging the improper termination and the deteriorated mode operating conditions that can cause data corruption. The difficulty arises from extension of the bus  908  past the terminator TB  914 , an improper termination that can cause signal degradation. 
   What is desired is a modified connector that can be used at Port A  904  and Port B  914  that is capable of generating an indication of the connection status of a port. What is further desired is a method for usage in combination with the modified connector that enables the system  900  to determine whether the bus  900  is properly configured. Changes in bus status indications determine how long to reset the bus  908  and timing of bus reset disable. 
   In an illustrative embodiment, a female connector that is separated into two electrically isolated parts attains the desired functionality. A connector shroud of the female connector is bisected, isolating metal ground pins and flanges on either side of the connector. In some configurations, one ground pin can be pulled high through a resistor to a voltage plane. The other ground pin is tied to ground. The pin that is pulled high can be monitored to detect connection of a mating connector to the female connector, for example using monitoring circuitry. When a cable with a male connector is connected to the female connector, the male connector shroud makes electrical contact to both sides of the female connector, electrically connecting the high and low sides of the female connector, enabling sensing that a cable is connected to the female connector. 
   A capability to determine whether a cable is connected to a female connector, without the other end of the cable being connected to anything, enables monitoring of the female connector for extensions of the bus that are not properly terminated. The capability enables bus configuration control functionality to isolate the connector, avoiding data corruption. 
   In some embodiments, the bus is a SCSI bus. In some embodiments, the female connector is a VHDCI connector. 
   The illustrative connector and associated method enables detection of bus configuration without monitoring of isolated pins on the female connector to determine when the pins are pulled to ground. The pins will only be pulled to ground if the other end of the cable is connected to a terminator or host bus adapter. 
   Referring to  FIG. 1 , a schematic block diagram shows an example of a computer system  100  including a bus system  102  that can connect a computer  110  to multiple peripheral devices. The peripheral devices can include internal devices  114  and  116  internal to the computer  110 , and external peripheral devices  118  and  120 . The illustrative computer  110  comprises a host bus adapter  112  and the two internal devices  114  and  116 . Examples of internal devices  114  and  116  may be internal disk drives, compact disk read-only memory (CD-ROM) devices, digital versatile disk ROM (DVD-ROM) devices, tape drives, any many others. External peripheral devices  118  and  120  may include printers, scanners, and others. Any suitable number of internal devices  114  and  116 , and external devices  118  and  120  may be connected to the bus system  102 . 
   The bus system  102  may be compliant with a standard, such as the Small Computer Systems Interface (SCSI) standard, or others. In one example, bus termination is to be supplied by a device at the end of the bus, internal device  116  in the illustrative embodiment. A cable  130 , such as a ribbon cable, can connect internal devices  114  and  116 , with a single connector  122  for each device. External devices  118  and  120  can be connected by a series of double-ended cables  132  and  134 . A first double-ended cable  132  connects a connector  124  on the computer  110  to external device  118 . A second double-ended cable  134  connects external device  118  and external device  120 . External device  120  has no cable attached, an open connector  126  that may be terminated with a terminator plug  128 . In one example, a Plug and Play SCSI standard mandates usage of the terminator plug  128 . Alternatively, the external device  120  can be terminated internally to the device  120 . 
   Referring to  FIG. 2A , a schematic pictorial and circuit diagram illustrates an embodiment of the disclosed connector  200 . The connector  200  comprises a plurality of contacts  240  capable of coupling to a corresponding plurality of conductors in a cable. A substrate supports the plurality of contacts  240  and an insulator layer encases at least a portion of the individual contacts  240 , mutually isolating the contacts  240 . In an illustrative embodiment, the connector  200  is a female connector comprising a shroud  202  separated into two electrically isolated parts  210  and  220 . The isolated parts  210  and  220  have mutually isolated metal ground contacts or pins  212  and  222 , respectively, and mutually isolated flanges  214  and  224 , respectively, on either side  210  and  220  of the connector  200 . One ground pin, for example ground pin  212 , can be pulled high through a resistor  208  to a voltage plane V+  206 . The other ground pin, in the example ground pin  222 , is connected to ground potential  205 . The electrically isolated parts  210  and  220  are electrically connected when a corresponding male connector is installed. Part  210  is connected to a sense line  204  that is pulled to the voltage plane V+  206  by resistor  208 . Part  220  is connected to ground potential  205 . With no male connector installed, the sense line  204  is pulled high. Circuitry  230  monitors the sense line  204  and detects the high state V+ when a male connector is not installed. 
   Referring to  FIG. 2B , a male connector  250  is installed into the female connector  200 . A connector shroud  252  of the male connector  250  makes electrical contact to both parts  210  and  220  of the female connector  200 . With the male connector  250  installed, the sense line  204  is pulled low through the male connector shroud  252  to ground potential  205 . The circuitry  230  senses the cable attachment to the female connector  200 . In the example of a SCSI bus connection, connection of the sense pin  204  to ground complies with the SCSI standard. 
   In the illustrative example, the connectors  200  and  250  are, respectively Very High Density Cable Interconnect (VHDCI), female and male connectors. 
   Referring to  FIG. 3 , a schematic block diagram shows an example of the usage of the illustrative female connector and the manner of operation to enable and disable an active termination circuit. In the example, connectors  300  and  302  each contain at least one female connector as illustrated in  FIGS. 2A and 2B . Each connector  300  and  302  has a sense line  204  pulled high if no associated male mating connector is attached, and pulled to ground if an associated male mating connector is attached. A terminators  304 A and  304 B, for example a SCSI terminator, terminate bi-directional data lines  306  for a single connector. One terminator bank for connectors  300  and  302 . Terminator  304  may be a commercially available active terminator circuit, or a functionally similar component. In other configurations, an electrically controlled switch may be used to switch a passive terminator circuit in or out. Terminator  304 A and  304 B have enable/disable input control signals. Voltage level depends on the particular terminator. Discrete control logic or FPGA/PLD chips can be used to monitor the connector sense lines, enable/disable termination, and control SCSI bus reset signals based on the desired operational technique. 
   The illustrative female connector enables detection of whether a corresponding male connector is installed. The illustrative female connector enables detection whether the configuration includes only one device with the connector, or some or all devices connected to the bus have the connector. Accordingly, the female connector can attain the desired functionality whether or not adopted as a standard. If one of the female connectors  300  and  302  are open, an external termination plug installed into the open female connector  300  or  302  forms an electrical contact in the manner of a corresponding male connector, automatically disabling the terminator  304  so that the external termination plug supplies termination. 
   In a SCSI application, the female connector contact is specified as a ground contact. For alternative applications, the line at the contact can be specified as a non-ground voltage with one part of the connector connected to the voltage and the other part resistively coupled to ground. In the alternative applications, mating connector presence is detected as a voltage on the resistor coupled to ground, or a current passing through the resistor. In further alternative examples, the two female connector parts can be monitored using any continuous measurement with a circuit being open if no mating connector is present and closed if a mating connector is present. In other examples, the connector can be a signal contact with one part connected to the signal and the second part connected to a high impedance signal detection circuit. If a mating connector is present, a signal is detected at the signal detection circuit. 
   Referring to  FIG. 4 , a pictorial drawing shows another example of a connector  400  that enables detection of a cable connection. In an illustrative example, a cable-side connector  400  is a 4 shielded 68-conductor SCSI device connector with two rows of ribbon contacts  440  connected 0.8 mm apart. The connector  400  comprises a plurality of contacts  440  capable of coupling to a corresponding plurality of conductors in a cable. A substrate  442  supports the plurality of contacts  440  and an insulator layer  444  encases at least a portion of the individual contacts  440 , mutually isolating the contacts  440 . The connector  400  comprises a shroud  402  separated into two electrically isolated parts  410  and  420 . The isolated parts  410  and  420  have mutually isolated metal ground contacts or pins  412  and  422 , respectively, and mutually isolated flanges  414  and  424 , respectively, on either side  410  and  420  of the connector  400 . 
   The cable-side connector  400  can be attached to a device-side connector  450 . A connector shroud  452  of the device-side connector  350  makes electrical contact to both segments  410  and  420  of the cable-side connector  400 . With the connectors attached, a sense line is pulled low through the device-side connector shroud  452  to ground potential enabling a monitor to sense cable attachment. 
   Referring to  FIG. 5 , a schematic block diagram shows an example of a bus architecture  500  that can utilize the illustrative connector to determine whether a cable is connected or unconnected. The illustrative bus architecture  500  enables valid SCSI connection for a dual ported controller card with a low voltage differential (LVD) SCSI data bus. In a specific embodiment SCSI standards specify a term power range between 3.0 volts and 5.25 volts, and a diff_sense signal voltage range between 0.7 volts and 1.9 volts to indicate an LVD connection. The SCSI standards further specify that at least one port is connected to a Host Bus Adapter (HBA) that supplies termination, term power, and diff_sense signal. The other port can be connected to another HBA or a terminator. 
   Term power and diff_sense signals are common signals that run through both ports A  510  and B  520  as in the SCSI specification (SPI through SP-4). If only one port is connected to an operating Host Bus Adapter (HBA), the term power and diff_sense signals remain although a valid front-end connection no longer exists. Accordingly both ports  510  and  520  are monitored to assure both have valid connections. 
   Some systems may use “auto-termination” circuitry to determine whether the SCSI bus has proper termination based on current sensed in any of multiple SCSI signals. Difficulties with the auto-termination approach result from usage of a variety of components with different electrical behavior and a resulting variation in current. The illustrative technique does not use current-sensing auto-termination techniques and presumes that a user has properly configured the Host Bus Adapter (HBA) with termination. 
   The technique determines whether a proper front-end connection exists by having the individual ports  510  and  520  isolate multiple ground pins, pull the ground pins high, and monitor the ground pins to determine whether the pins are pulled low due to a connection. At least two pins are isolated to avoid a condition in which an HBA also has one ground pin isolated for the same reason. The technique utilizes the circuit diagrammed in  FIG. 6  to manage the manner in which a pin that is not pulled down due to the pin&#39;s condition as isolated and pulled up on the other end. 
   The individual signals connected to an isolated ground pin on a port is connected to two ports of a control device  610 , such as a Field Programmable Gate Array (FPGA) or Programmable Logic Device (PLD). One control device monitoring port, for example S 1i  or S 2i , is configured as an input port, and a second port, for example S 1o  or S 2o , is set as an output port and tri-stated (disabled) when not pulling the signal low. At least two isolated ground pins are allocated per connector port. If one signal is pulled low as a result of a connection, that signal alerts the control device  610  to pull the second line down so that the other device will also sense the connection. Logic executing on the control device  610  transfers to another state and waits for at least one signal to go high, indicating a disconnection. Upon disconnection, all output signals S 1o  and S 2o  are tri-stated. 
   Referring to TABLE I, a truth table shows state relationships for two input signals and two output signals with state signals associated with the output signals. 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
               TABLE I 
             
             
                 
             
             
                 
               Input S2(I2) 
               Input S1(I1) 
               State 1 
               State 0 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               
                 0 
               
               
                 0 
               
               
                 0 
               
               
                 0 
               
               
                 0 
               
             
             
               
                 1 
               
               
                 0 
               
               
                 0 
               
               
                 0 
               
               
                 1 
               
             
             
               
                 2 
               
               
                 0 
               
               
                 0 
               
               
                 1 
               
               
                 0 
               
             
             
               3 
               0 
               0 
               1 
               1 
             
             
               
                 4 
               
               
                 0 
               
               
                 1 
               
               
                 0 
               
               
                 0 
               
             
             
               
                 5 
               
               
                 0 
               
               
                 1 
               
               
                 0 
               
               
                 1 
               
             
             
               
                 6 
               
               
                 0 
               
               
                 1 
               
               
                 1 
               
               
                 0 
               
             
             
               7 
               0 
               1 
               1 
               1 
             
             
               
                 8 
               
               
                 1 
               
               
                 0 
               
               
                 0 
               
               
                 0 
               
             
             
               
                 9 
               
               
                 1 
               
               
                 0 
               
               
                 0 
               
               
                 1 
               
             
             
               
                 10 
               
               
                 1 
               
               
                 0 
               
               
                 1 
               
               
                 0 
               
             
             
               11 
               1 
               0 
               1 
               1 
             
             
               
                 12 
               
               
                 1 
               
               
                 1 
               
               
                 0 
               
               
                 0 
               
             
             
               
                 13 
               
               
                 1 
               
               
                 1 
               
               
                 0 
               
               
                 1 
               
             
             
               
                 14 
               
               
                 1 
               
               
                 1 
               
               
                 1 
               
               
                 0 
               
             
             
               
                 15 
               
               
                 1 
               
               
                 1 
               
               
                 1 
               
               
                 1 
               
             
             
                 
             
             
               Valid states are indicated in bold.  
             
           
        
       
     
   
   The occurrence of a connection at signal S 1i  causes control device  610  to transition signals S 1i , S 2i , S 2o , S 1o  through states  0 - 4 - 6 - 14  as shown in Table II. 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
               TABLE II 
             
             
                 
             
             
                 
                 
                 
               State of 
               State of 
             
             
               Path 
               Input S 2I   
               Input S 1i   
               Output S 2o   
               Output S 1o   
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               0 
               0 
               0 
               0 
               0 
             
             
               4 
               0 
               1 
               0 
               0 
             
             
               6 
               0 
               1 
               1 
               0 
             
             
               14 
               1 
               1 
               1 
               0 
             
             
                 
             
           
        
       
     
   
   When a disconnection occurs at signal S 1i , the state of signals S 1i , S 2i , S 2o , S 1o  through paths  14 - 10 - 8 - 0  as shown in Table III. 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
               TABLE III 
             
             
                 
             
             
                 
                 
                 
               State of 
               State of 
             
             
               Path 
               Input S 2I   
               Input S 1i   
               Output S 2o   
               Output S 1o   
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               14 
               1 
               1 
               1 
               0 
             
             
               10 
               1 
               0 
               1 
               0 
             
             
               8 
               1 
               0 
               0 
               0 
             
             
               0 
               0 
               0 
               0 
               0 
             
             
                 
             
           
        
       
     
   
   When a connection is sensed at Input S 2 , the state transition of signals S 1i , S 2i , S 2o , S 1o  includes paths  0 - 8 - 9 - 13  as shown in Table IV. 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
               TABLE IV 
             
             
                 
             
             
                 
                 
                 
               State of 
               State of 
             
             
               Path 
               Input S 2i   
               Input S 1i   
               Output S 2o   
               Output S 1o   
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               0 
               0 
               0 
               0 
               0 
             
             
               8 
               1 
               0 
               0 
               0 
             
             
               9 
               1 
               0 
               0 
               1 
             
             
               13 
               1 
               1 
               0 
               1 
             
             
                 
             
           
        
       
     
   
   Signals S 1i , S 2i , S 2o , S 1o  transition through paths  13 - 5 - 4 - 0 , as shown in Table V, when a disconnection occurs at input port S 2 . 
   
     
       
             
             
             
             
             
           
             
             
             
             
             
           
         
             
               TABLE V 
             
             
                 
             
             
                 
                 
                 
               State of 
               State of 
             
             
               Path 
               Input S 2i   
               Input S 1i   
               Output S 2o   
               Output S 1o   
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               13 
               1 
               1 
               0 
               1 
             
             
               5 
               0 
               1 
               0 
               1 
             
             
               4 
               0 
               1 
               0 
               0 
             
             
               0 
               0 
               0 
               0 
               0 
             
             
                 
             
           
        
       
     
   
   Information regarding whether a connection or disconnection is occurring is used to determine the next state. State information follows from the fact that when a disconnection occurs at signal S 1i , or a connection occurs at signal S 2i   , the states of signals S   1i , S 2i , S 1o , S 2o  transition through path  8  (1000). Path  4  (0100) is another common path that is transitioned during a disconnection at signal S 1o , and a connection at port S 2o . State machines  700  and  800  shown in  FIGS. 7 and 8 , respectively, can be used to determine the next transition state. Then state information, in turn, can be used to determine: (1) whether a connector is being attached to or removed from circuit  600  shown in  FIG. 6 , (2) the next state based on the values of S 1i , S 2i , and (3) whether a connection is being made or broken. 
   The embodiment of state machine  700  shown in  FIG. 7  includes a disconnected state 0 and a connected state 1. The circles and arrows describe how state machine  700  moves from one state to another. In general, the circles in a state machine represent a particular value of the state variable. The lines with arrows describe how the state machine transitions from one state to the next state. One or more boolean expressions are associated with each transition line to show the criteria for a transition from one state to another. If the boolean expression is TRUE and the current state is the state at the source of the arrowed line, the state machine will transition to the destination state on the next clock cycle. The diagram also shows one or more sets of the values of the output variables during each state next to the circle representing the state. 
   In state machine  700 , the input signals S 1i , S 2i , and connection status is indicated by a Boolean expression with three numbers representing in order from left to right, the state of the input signals S 2i  and S 1i , and connection status, where each number can have the value of 1 or 0 depending on the corresponding state of the parameter. For example, States 000, 010 and 100 indicate no connection to a device. A transition from disconnected to connected occurs when State 110 is detected. Similarly, States 011, 101, and 111 indicate a connection to a device, and a transition from connected to disconnected occurs when State 001 is detected. 
   State machine  800  determines the state of signals S 1i , S 2i , S 1o , and S 2o  based on connection status and a change in either input signal S 1i  or S 2i . In some embodiments, the transitions between states follow the paths shown in Tables IV, V, VI, and VII. Input signals S 1i , S 2i  and connection status are indicated by a Boolean expression with three numbers representing in order from left to right the state of the input signals S 2i  and S 1i , and connection status. Each number can have the value of 1 or 0 depending on the corresponding state of the parameter. States of the output signals S 2o  and S 1o  are shown as a Boolean expression in the state circles 00, 01, 10 and 11. 
   Although the illustrative example describes a particular type of bus connector, the claimed elements and techniques may be utilized with other bus connector types or configurations. For example, although the illustrative connector has a conductive shroud that is separated into isolated parts that are electrically connected when a mating connector is attached, other structures in the connector, such as a housing or casing, may be separated to supply the utilized isolation. The illustrative buses, connectors, and methods are particularly described in utilization with a SCSI bus standard. The claimed elements and methods may be used under other interface standards. For example, although the disclosed system is described in terms of a SCSI bus system, the illustrative connector can be used for general detection of the presence of a mating connector in any bus system and is not limited to SCSI systems.