Abstract:
An analog Ethernet detector determines if an IEEE 1394b long haul application using Category 5 (CAT 5 UTP) cable, is connected to an Ethernet which share certain pins of the RJ45 connector used to connect devices to the CAT 5 cable. The detector does not require a processor core or clocking and can be built as a completely analog device.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an Ethernet detector and more specifically to an analog Ethernet detector for IEEE 1394b Long-Haul Applications. 
   The Institute of Electrical and Electronics Engineers has approved a 1394b Standard which is poised to become the home networking Standard of choice for connecting consumer electronics devices such as audio/visual devices with personal-computers. The IEEE 1394b Standard can provide high-speed 100 Mb/second transmission speeds at distances up to 100 m over Standard Category 5 (CAT 5) cable. This cable is sometimes referred to as CAT5 UTP, for untwisted pair cable. The IEEE 1394b Standard is a low power yet high-speed, plug and play system which supports both isochronous data such as video and voice and asynchronous data such as IP. The ability to utilize CAT 5 cable is a big advantage because many homes today are already wired with this type of cable. This will allow consumers the ability to provide advanced home network and create a high-speed connectivity between their living room audio/video components and their home office. 
   The ability to transmit on CAT 5 cable, which makes this system so attractive, is also the potential cause of a problem for the consumer. The reason that consumers have CAT 5 cable wired throughout their home is for an Ethernet connection and not for connecting consumer audio/visual components to their home office. The connectors for IEEE 1394b and to the Ethernet on CAT 5 cable are identical and the consumer may not know which wiring is connected to the Ethernet and which wiring is for the IEEE 1394b connection. Worse, the current embodiment of IEEE 1394b shares some pins as an Ethernet. If the consumer were to connect a IEEE 1394b device to the Ethernet, the data that is sent from the device over the Ethernet may interfere with the network or computers connected thereto. Accordingly there is a need for a circuit to detect connection to the Ethernet. 
   There is a need for an analog circuit that is compatible with any S100 1394b compliant device to detect connection to an Ethernet without the need for a processor core or a timing circuit. 
   SUMMARY OF THE INVENTION 
   It is a general object of the invention to provide an analog Ethernet detector. This and other objects and features of the present invention are provided, in accordance with one aspect of the invention by an analog Ethernet detector comprising a first signal detector coupled to transmit conductors of an Ethernet. A second signal detector is coupled to receive conductors of an Ethernet. A third signal detector is coupled to a non-Ethernet transmit signal. A first logic circuit is coupled to an output to the first and third signal detectors for determining that a signal on the transmit conductors is not a non-Ethernet signal. A second logic circuit is coupled to an output from the first logic circuit and the second signal detector for generating an Ethernet_detected signal. 
   Another aspect of the invention includes a method of detecting that an IEEE 1394b signal is connected to an Ethernet comprising detecting a signal having a predetermined voltage level on Ethernet transmit conductors and generating a first signal. Detecting an IEEE 1394b signal generated for transmission on the transmit conductors and generating a second signal. Detecting an Ethernet transmission having a predetermined voltage level on Ethernet receive conductors and generating a third signal. Generating a first logic signal from the first and second signals. Generating a second logic signal indicating that Ethernet has been detected from the first logic signal and the third signal. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a circuit diagram in block form of a portion of the transmit circuit for a IEEE 1394b to CAT 5 interface; and 
       FIG. 2A  is a circuit diagram for an embodiment of the present invention according to the current IEEE 1394b Standard,  FIG. 2B  is a first reset circuit for the latch of the circuit of  FIG. 2A , and  FIG. 2C  is a second reset circuit for the latch of the circuit of  FIG. 2A . 
   

   DETAILED DESCRIPTION 
   The IEEE 1394b Standard utilizes pins  1  and  2  on a CAT5 UTP for transmission to the network and pins  7  and  8  for reception from the network. Ethernet connections utilize pins  1  and  2  to transmit to the network and pins  3  and  6  to receive data from the network. Pins  1  and  2  are therefore used by both an IEEE 1394b network and an Ethernet for transmission to the network. This is done to provide backwards compatibility to the older IEEE 1394a systems in which only four pairs are provided. Thus, both the Ethernet and IEEE 1394b systems utilize pins  1  and  2  for transmission. This problem is further complicated by the fact that Ethernet connections can use two types of cables. Crossover cables are used to connect the transmit pins  1  and  2  to the reception pins  3  and  6  in some applications. However, some Ethernet devices such as hubs have the crossover built into the device, and thus crossover cable cannot be used. In these situations, patch cables are used. In patch cables pins  1  and  2  on the transmit side are wired to pins  1  and  2  of the reception side and pins  3  and  6  on the transmit side are wired pins  3  and  6  of the reception side of the cable. Therefore, it is necessary to look for Ethernet transmissions on pins  1  and  2  as well as  3  and  6 . 
     FIG. 1  shows a simplified block diagram of a transmit circuit for an IEEE 1394b interface generally as  100 . Pins  102  and  104  are located on an IEEE 1394b interface connector and the signals provided at these terminals are coupled via the capacitors  106  and  108  to comparator  110 . The capacitors provide AC coupling to remove any DC component of the signals applied to pins  102  and  104 . If the signal levels on pins  102  and  106  are sufficiently high, the comparator  110  provides an output on lines  112  and  114  to differential output amplifier  116  which amplifies the signals and provides a differential output to pins  118  and  120 , respectively. These correspond to pins  1  and  2  on the CAT 5 cable. The output of the comparator  110  on lines  112  and  114  are also coupled to the inputs  202  of  FIG. 2 . 
   Referring to  FIG. 2 , the present invention in accordance with the current IEEE 1394b Standard, is shown generally as  200 . The circuit comprises three voltage detectors  208 ,  210 ,  212 , all of known design. Each of these detectors  208 ,  210  and  212  responds to a predetermined voltage level to detect a signal present on the input lines. Pins  3  and  6  of the RJ45 connector are the receive pins  204  which are connected to voltage detector  210 . If there is a voltage of sufficient magnitude to be detected by detector  210 , this means that a signal received on pins  3  and  6  of the RJ45 connector must be an Ethernet signal. The output of detector  210  is fed into one input of a two input OR gate  218 . The output of OR gate  218  is the Ethernet_detected signal which is applied to the set input of latch to  220 . The output of latch  220  is the Ethernet_connected signal on line  222 . This can be connected to other devices (not shown) such as a LED, for example, to indicate to a consumer that the device has been plugged into an Ethernet_connected socket and not an IEEE 1394b connected socket. 
   Pins  1  and  2  of the RJ45 connector are coupled to lines  206  and which are input to the voltage detector  212 . If the voltage across pins  1  and  2  is of sufficient magnitude, the detector will provide a digital one output which will indicate one of two possibilities. One possibility is that there is a signal on the Ethernet, in which case the circuit is to be disabled. Another possibility is that there is a signal at terminals  102 , 104  which is being transmitted across from the IEEE 1394b source. Thus a simple output from detector  212  fails to provide sufficient information. The output of detector  212  is coupled to AND gate  216  which has a second input coupled to the output of detector  208  via inverter  214 . The lines  202  from the output  112 ,  114  of the comparator  110  are coupled to the input of detector  208 . If the signal on outputs  112 ,  114  are of sufficient amplitude to indicate that an IEEE 1394b signal is to be transmitted on the CAT5 cable, then detector  208  will provide a digital one signal at its output, which will be inverted to a digital zero by inverter  214  and input to the 2-input AND gate  216 . Thus there will be an output from AND gate  216  only when a signal is detected on lines  206  and not detected on lines  202 . A digital one signal output from AND gate  216  and from detector  210  are input to the OR gate  218  which generates a digital one as the Ethernet_detected signal, which is applied to the set input to latch  220 . This will set the latch which will provide an Ethernet_connected signal on line  222  to activate a LED, for example. The Ethernet_connected signal is also used to disable the amplifier  116  via a disable input or by disconnecting power to the amplifier. 
   It is desirable to have latch  220  set because signals on the Ethernet are not continuous and may have a 4 milliseconds spacing between them. Therefore, without presence of latch  220 , the circuit would be turning on and off depending upon the transmissions across the Ethernet or the transmissions from the IEEE 1394b device. Resetting of the latch can be accomplished manually in one of two ways. A reset latch signal can be provided on line  224  from manually operated means to reset the latch, as is known in the art. In  FIG. 2B  such a reset circuit is generally shown as  230 . A pushbutton switch  236  switches the reset input  224  to the latch  220  between ground  234  and the voltage supply  234  for the device. Optional debounce circuit  238  will eliminate the effects of bouncing of the switch contacts, as is known in the art. Another way to reset the latch is to operate the push button switch  232  which interrupts the supply of voltage from voltage supply  230  to the input  234  to the latch  220  or the entire circuit shown in  FIG. 2 . This is illustrated in  FIG. 2C  generally as  250 . The voltage supply  250  to the circuit of  FIG. 2A  passes through pushbutton switch  254  before being applied as the input voltage  256  for the circuit. Pushing pushbutton switch  254  de-powers the circuit. On power-up, circuitry on the integrated circuit (not shown), which is well known in the art, will cause the latch to be in the unlatched state. 
   The circuit shown in  FIG. 2  provides a simple analog circuit to determine if an IEEE 1394b device is connected to an Ethernet rather than to an IEEE 1394b CAT 5 connection. The circuit does not require a processor core or clocking and can be built as a completely analog device at low-cost in a small size package. 
   While the invention has been shown and described with reference to preferred embodiments thereof, it is well understood by those skilled in the art that various changes and modifications can be made in the invention without departing from the spirit and scope of the invention as defined by the appended claims.