Abstract:
The described embodiments relate to systems of communicably coupling electronic appliances and resultant methods. In one exemplary embodiment, the method couples an electronic appliance to a data transfer network. It monitors a status of a power supply of said electronic appliance and transmits a signal on the data transfer network when said status changes.

Description:
BACKGROUND  
         [0001]    As electronic devices or appliances, such as computers, become more powerful, a great amount of effort has been spent to allow the appliances to share data with one another. Of the available systems, the IEEE 1394 serial bus network or “Firewire” thus far has proven to be one of the more efficient systems. The IEEE 1394 system allows high-speed data transfer between various IEEE 1394 compliant appliances attached to the system.  
           [0002]    Unfortunately, the IEEE 1394 system still has shortcomings that limit its performance. Most notably, if an appliance connected to an IEEE 1394 system loses power, the other appliances remain unaware of this condition and may repeatedly send data to the effected appliance. This situation needlessly ties-up available bandwidth. Additionally, data that is routed through the effected appliance will be blocked and can cause data to be backed-up on the system.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0003]    The same numbers are used throughout the drawings to reference like features and components.  
         [0004]    [0004]FIG. 1 is a perspective view of an exemplary printing appliance in accordance with one embodiment.  
         [0005]    [0005]FIG. 2 is a block diagram of an exemplary printing appliance in accordance with one embodiment.  
         [0006]    [0006]FIG. 3 is a block diagram of an exemplary computing appliance in accordance with one embodiment.  
         [0007]    [0007]FIG. 4 is a diagram of an exemplary system in accordance with one embodiment.  
         [0008]    [0008]FIG. 5 is a block diagram of exemplary component of a system in accordance with one embodiment.  
         [0009]    [0009]FIG. 6 is a block diagram of exemplary component of a system in accordance with one embodiment.  
         [0010]    [0010]FIG. 7 is a flow chart of an exemplary logic circuit in accordance with one embodiment.  
         [0011]    [0011]FIG. 8 is a schematic of an exemplary logic circuit in accordance with one embodiment.  
         [0012]    [0012]FIG. 9 is a flow chart showing steps in a method in accordance with one embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0013]    Overview  
         [0014]    The described embodiments relate to a system that allows electronic devices or appliances to send data to one another. The described system can increase the efficiency of data transmission. Electronic devices can include computers, printers, digital cameras, and scanners among others. In one exemplary embodiment, the system may comprise an IEEE 1394 serial bus network. A bus is a transmission path on which signals are dropped off or picked up by electronic devices on the system. An IEEE 1394 serial bus is a bus complying with standards established by the Institute of Electrical and Electronics Engineers (IEEE). The system can include various IEEE 1394 compliant appliances that can be connected to the IEEE 1394 serial bus. The system also includes one or more circuit(s) for the appliance(s). The circuit(s) monitors a status of the appliance(s) to improve system performance.  
         [0015]    The IEEE 1394 standard contains various protocols that require certain features of any appliance configured to the system. These features include IEEE 1394 compliant electrical devices that form an interface between the appliance and the serial bus. In some exemplary embodiments, these electrical devices comprise integrated circuit chips, though other suitable embodiments can be constructed. The electrical devices provide varying layers of functionality to the system. Two of the functional layers are termed the physical layer and the link layer.  
         [0016]    The IEEE 1394 protocols for the physical layer and the link layer allow the circuit(s) to increase the performance of the system. The circuits can monitor a status of the appliance that can affect the system. In some exemplary embodiments, the monitored status can be a power supply status of the appliance. If the circuit detects a change in the power supply status of the appliance, it can cause an IEEE 1394 physical layer chip coupled to the circuit to reset. According to IEEE 1394 protocols, specifically the IEEE 1394 compliant integrated circuits specifications, a physical layer reset will cause a system bus reset that causes each appliance on the system to provide a self-identification (self-ID).  
         [0017]    The self-ID data from each appliance includes a status report regarding the appliance&#39;s link layer functionality. The status report will indicate either that the link layer is active or inactive. In the case of an inactive link layer, the other appliances on the system will not send data to that appliance. This can prevent a functioning or active appliance from sending data repeatedly to a non-functioning or inactive appliance that cannot receive the data. Additionally, in the case of a power failure to an individual appliance, that appliance&#39;s physical layer can be switched to a secondary power supply provided by the system on IEEE 1394 compliant serial cables. This secondary power supply can allow data to flow through the inactive appliance&#39;s physical layer on a path from one active appliance to another. More information regarding IEEE 1394 technical specifications can be found at http://www.1394ta.org/Technology/Specifications/index.htm.  
         [0018]    The various components described below may not be illustrated accurately as far as their size is concerned. Rather, the included figures are intended as diagrammatic representations to illustrate to the reader various concepts that are described herein.  
         [0019]    Exemplary Printer System  
         [0020]    [0020]FIG. 1 depicts an exemplary appliance. In this illustration, the appliance is a printer  100 . It will be appreciated and understood that the illustrated printer constitutes but one appliance or device and is not intended to be limiting in any way. Accordingly, other appliances can be used in connection with the inventive techniques and systems described herein. Additional exemplary appliances will be described below. These other appliances can have components that are different from those described below in relations to printer  100 .  
         [0021]    [0021]FIG. 2 is a block diagram showing exemplary components of a printing device in the form of a printer  100  in accordance with one embodiment. Printer  100  can include a processor  202 , an electrically erasable programmable read-only memory (EEPROM)  204 , and a random access memory (RAM)  206 . Processor  202  processes various instructions necessary to operate the printer  100  and communicate with other devices. EEPROM  204  and RAM  206  store various information such as configuration information, fonts, templates, data being printed, and menu structure information. Although not shown in FIG. 2, a particular printer may also contain a ROM (non-erasable) in place of or in addition to EEPROM  204 .  
         [0022]    Printer  100  can also include a non-volatile read/write mass memory  208 , and an interface port  210 . The non-volatile memory  208  provides additional storage for data being printed or other information used by the printer  100 . Although both RAM  206  and non-volatile memory  208  are illustrated in FIG. 2, a particular printer can contain either RAM  206  or non-volatile memory  208 , depending on the storage needs of the printer. For example, an inexpensive printer may contain a small amount of RAM  206  and no non-volatile memory  208 , thereby reducing the manufacturing cost of the printer. Interface port  210  provides a connection between printer  100  and a data communication network. The interface port  210  provides a data communication path between printer  100  and other appliances, such as a workstation, server, or other computing appliance. The interface port  210  can be an IEEE  1394  compliant serial bus port.  
         [0023]    Printer  100  also includes a print unit  214  that includes mechanisms that are arranged to selectively apply ink (e.g., liquid ink, toner, etc.) to a print media (e.g., paper, transparencies, plastic, fabric, etc.) in accordance with print data within a print job. Thus, for example, print unit  214  can include a conventional laser printing mechanism that selectively causes toner to be applied to an intermediate surface of a drum or belt. The intermediate surface can then be brought within close proximity of a print media in a manner that causes the toner to be transferred to the print media in a controlled fashion. The toner on the print media can then be more permanently fixed to the print media, for example, by selectively applying thermal energy to the toner. Print unit  214  can also be configured to support duplex printing, for example, by selectively flipping or turning the print media as required to print on both sides.  
         [0024]    Those skilled in the art will recognize that there are many different types of print units available, and that for the purposes of the present embodiments print unit  214  can include any of these various types. For example, the print unit can also be configured in an ink jet configuration where fluid ink is ejected from individual firing chambers.  
         [0025]    Printer  100  may also contain a user interface/menu browser  216  and a display panel  218 . User interface/menu browser  216  allows the user of the printer to navigate the printer&#39;s menu structure. User interface  216  may be a series of buttons, switches, or other indicators that are manipulated by the user of the printer. The printer display or display panel  218  is a graphical display that provides information regarding the status of the printer and the current options available through the menu structure.  
         [0026]    Exemplary Host Computer  
         [0027]    For purposes of understanding various structures associated with an exemplary host computer, consider FIG. 3. FIG. 3 is a block diagram showing exemplary components of a host computer  300 . Host computer  300  may include a processor  302 , a memory  304  (such as ROM and RAM), user input devices  306 , a disk drive  308 , interface port  310  for inputting and outputting data, a floppy disk drive  312 , and a CD-ROM drive  314 . Processor  302  performs various instructions to control the operation of computer  300 . Memory  304 , disk drive  308 , and floppy disk drive  312 , and CD-ROM drive  314  provide data storage mechanisms. User input devices  306  include a keyboard, mouse, pointing device, or other mechanism for inputting information to computer  300 . Interface port  310  provides a mechanism for computer  300  to communicate with other devices. The interface port can be configured according to IEEE 1394 protocols. The computer described here can be one type of suitable computing device as it relates to the described embodiments, others can include but are not limited to personal computers, super computers, logic sequencers, state machines, and other appliances containing a computing device. Many commonly available electronic appliances can comprise computing devices.  
         [0028]    Exemplary Embodiment  
         [0029]    FIGS.  4 - 6  show an exemplary system. In these exemplary embodiments, the system can comprise a network  400 . As shown in FIG. 4, the network  400  can be an IEEE 1394 compliant network. The IEEE 1394 standard provides a high-speed network for connecting digital appliances and thereby providing a universal I/O connection or port. FIG. 4 shows four appliances. The appliances comprise a notebook or laptop computer  300   a , a desktop computer  300   b , a scanner  402 , and a printer  100   a.  Each of the appliances is coupled to a circuit  404 . In the illustrate embodiment, circuits  404   a ,  404   b ,  404   c  and  404   d  are coupled to notebook computer  300   a , desktop computer  300   b , scanner  402 , and printer  100   a  respectively. The circuit(s)  404   a - 404   d  may comprise logic circuit(s), interface circuit(s), arbiter circuit(s), processing circuit(s), communications circuit(s), and/or data conversion circuits or a combination thereof, among others. Various exemplary circuits will be discussed below. For the purposes of illustration, the circuits  404   a - 404   d  have been shown as separate distinct units, but as will be discussed below in other exemplary embodiments, the circuit&#39;s functionality may be incorporated onto other components.  
         [0030]    In addition to being connected to a circuit, each of the appliances  100   a ,  300   a ,  300   b , and  402  is connected to the system at a node, indicated generally herein as node  406 . Node  406   a ,  406   b ,  406   c , and  406   d  are coupled to appliances  300   a ,  300   b ,  402 , and  100   a  respectively. Various sections of an IEEE  1394  compliant serial cable  408  connect the various appliances  300   a ,  300   b ,  402 , and  100   a  at the nodes  406   a ,  406   b ,  406   c , and  406   d . A node, such as nodes  406   a ,  406   b ,  406   c , and  406   d , is considered a logical entity with a unique address on the system structure. Each node provides an identification ROM, a standardized set of control registers and its own address space. The node&#39;s functionality can comprise one or more IEEE 1394 compliant electrical devices  407  that form an interface between the appliance and the serial bus network. In some exemplary embodiments, these electrical devices  407  can comprise integrated circuits, though other suitable embodiments can be constructed.  
         [0031]    Existing IEEE 1394 compliant networks may allow appliances, such as appliances  300   a ,  300   b ,  402 , and  100   a , to be added and removed from the network while the system is active. If an appliance is so added or removed the network will then automatically reconfigure itself according to IEEE 1394 protocols. This reconfiguration includes causing each appliance to generate a self-ID signal. The self-ID preferably contains data that allows each appliance to know what other appliances are on the network, the appliances&#39; characteristics, and at what node they are located. This process will be discussed in more detail below.  
         [0032]    The described embodiments allow individual appliances and corresponding IEEE 1394 compliant serial cable  408  to be added or removed as desired while the network remains functional. For example, a new appliance can be connected at any available node. With this type of configuration, any data that the new appliance sends or receives travels through the node of the appliance to which it is connected. Thus, intermediary appliances can serve as relays through which data passes between other appliances on the system. This daisy chain configuration can be seen in FIG. 4, where the scanner  402  is connected to the node at the notebook computer  300   a . Another appliance can be connected to the scanner&#39;s node, etc.  
         [0033]    This configurability allows the system to be continually adapted to new configurations. However, in earlier applications, data that travels through an intermediary node and appliance en route to a destination appliance can be blocked if the intermediary appliance becomes unavailable. For example, in previous configurations, data sent from desktop computer  300   b  to scanner  402  would travel through node  406   a  and notebook computer  300   a . If the notebook computer  300   a  stopped functioning, from for example, losing its power supply, the data would be blocked at the notebook computer  300   a  and be unable to reach the scanner  402 .  
         [0034]    As mentioned above, existing IEEE 1394 networks provide some self-monitoring capabilities. The self-monitoring capabilities utilize the IEEE 1394 protocols and layered functionality. An IEEE 1394 network achieves its functionality by having various communication (protocol) layers, each of which performs a different function.  
         [0035]    [0035]FIG. 5 shows various protocol layers  500  as they occur at each node in one exemplary embodiment. As can be seen, the protocol layers range from the physical layer  504 , to the link layer  506 , the transaction layer  508 , and the application layer  510 . The physical layer  504  and the link layer  506  comprise the hardware layers. The hardware layers are relatively non-configurable between applications whereas the upper layers, such as the transaction layer  508  and the application layer  510 , are software based and can be configured for specific applications. There can also be a serial bus management layer  512  that manages the connection conditions for the connected appliances, their Ids, and the network configuration.  
         [0036]    [0036]FIG. 6 shows another exemplary embodiment of the various protocol layers  500   a . In this example, the logic circuit  404   a  is contained on the physical layer  504   a . This can allow a single integrated circuit (chip) or die to perform the functions of the physical layer and of the circuit. Other alternative exemplary configurations can be constructed by the skilled artisan.  
         [0037]    Referring again to FIGS. 5 and 6, the physical layer  504  provides the electrical and mechanical connection between an appliance, such as notebook computer  300   a , and the IEEE 1394 cable  408 . The link layer  506  also comprises hardware and data transmission takes place between the appliances on the system  400  via the link layer.  
         [0038]    At an individual appliance, such as notebook computer  300   a , each of the different functional layers can be on a separate IEEE 1394 compliant chip. Alternatively, some or all of the layers can share a chip. IEEE 1394 chips are commercially available from various manufacturers, such as Texas Instruments, among others.  
         [0039]    The IEEE 1394 system  400  can also provide power to an appliance&#39;s physical layer  504 . The IEEE protocols allow the physical layer to supply approximately three watts ( 3   w ) to an appliance, such as notebook computer  300   a . This is generally insufficient energy to power the entire appliance, but can allow portions of the appliance to remain functional. However, powering the physical layer  504  can allow data to pass through an unavailable appliance, such as one having a malfunctioning or deactivated power supply.  
         [0040]    IEEE 1394 protocols require all appliances, such as  300   a ,  300   b ,  402 , and  100   a  on the network  400  to conduct a self-ID when an appliance is added or removed from the network. However, the existing network is very limited in what conditions trigger a self-ID. For example, with the existing technology the various appliances comprising the network have no way of knowing if an appliance on the network becomes unable to receive data.  
         [0041]    In this situation, an unaffected appliance(s) may send data repeatedly to the affected appliance since it has no way of knowing that the data cannot be received. Eventually, a time-out protocol should stop the sending appliance from further attempts to send the data, but during the interim, much of the network&#39;s potential bandwidth is needlessly and uselessly tied-up. In addition, as mentioned above, with the daisy chain configuration, data may have to travel through intermediary nodes on the way to a designated appliance. If one of these nodes is not functioning it can cause the data to be blocked at the nonfunctioning appliance.  
         [0042]    This problem can be minimized by increasing the information available to the various appliances on the network. One way this can be achieved is with the addition of circuit  404 . The circuit can comprise a logic circuit, among others (non-limiting examples of which were given above). The logic circuit can improve the functionality of the IEEE 1394 compliant network by monitoring a condition of an appliance on the network. If a monitored condition changes as defined by the logic circuit, the logic circuit can indirectly make the information available to the other appliances on the system by utilizing the IEEE 1394 protocols. One way that this can be accomplished is shown in FIG. 7.  
         [0043]    [0043]FIG. 7 shows an exemplary embodiment of the functionality of circuit  404  that can monitor a condition or status of an appliance  702  to which it is connected. In this exemplary embodiment, circuit  404  comprises a logic circuit. At  704 , if the monitored condition changes, the circuit can provide notification of the condition to the other appliances on a network  706 . If the condition did not change the circuit returns to  702 . In this exemplary embodiment, the circuit can monitor a power supply status of the appliance. A change in the power supply status causes the circuit to provide a system notification of the change.  
         [0044]    One way that the logic circuit can provide this notification is to utilize the protocols of the IEEE 1394 standard. Under the IEEE 1394 protocols, a reset condition of any physical layer chip will cause a reset condition of all appliances on the network. The reset condition includes a self-ID from each appliance and the self-ID includes a link layer status.  
         [0045]    If the monitored appliance  702  looses power, the logic circuit  704  can cause a physical layer reset for that appliance. As discussed above, the physical layer reset will cause a system wide reset that causes all appliances to self-ID. If the monitored appliance has lost power, its link layer will be nonfunctional, and its self-ID will show that its link layer is non-functional or unavailable.  
         [0046]    As described above, the affected appliance cannot receive data when its link layer is not functional. Given this information, the other appliances on the system then will not send data to the affected appliance, thus maintaining the available bandwidth for other data streams.  
         [0047]    The logic circuit can also cause the affected appliance&#39;s physical layer to be powered by the system power so that data can flow through the affected device&#39;s physical layer to a destination appliance. For example, refer again to FIG. 4, if logic circuit  404   a  detects a drop in the power supply of notebook computer  300   a , the logic circuit causes a reset of the appliance&#39;s physical layer  504 . This reset causes a system wide reset that requires each appliance to self-ID. The self-ID from notebook computer  300   a  shows that its link layer  506  is down. If desktop computer  300   b  was going to send data to notebook computer  300   a  the link layer non-functional condition would allow it to take alternative action, such as storing the data until the notebook computer became available. Additionally, the logic circuit  404   a  having caused the physical layer chip to be switched to system power can allow scanner  402  to send data through the physical layer chip of notebook computer  300   a  thus allowing the system to remain functional.  
         [0048]    [0048]FIG. 8 shows one way of assembling an exemplary logic circuit  404   b . This embodiment triggers a physical layer reset if the monitored appliance is powered up or powered down, or if physical layer is switched from primary to bus power. Other exemplary embodiments can be designed to trigger a reset based on other conditions. For example, a satisfactory embodiment can cause a reset only when the power supply goes down.  
         [0049]    Referring specifically now to the embodiment shown in FIG. 8, an ASIC reset bar  802  from the printer controller chip is received at NAND gate  804 . The output of the NAND gate  804  is coupled with opto-isolator  806 . The opto-isolator also receives a signal from a 3.3-volt DC power supply  807  that is referenced to a digital common or ground  808 . Between the power supply and the opto-isoltor lies a 1,000 ohm resistor  810 . Both the ASIC reset  802  and NAND gate  804  are connected to digital common ground  808 . The opto-isolator  806  ensures galvanic isolation between the digital common  808  and the physical layer common  814  in accordance with IEEE 1394 specifications and can otherwise be eliminated. The signal of the output of NAND  804  is optically transmitted by LED driver  806  to optical transistor  812 . The transistor is driven by a 3.3 volt DC power supply  813  that is referenced to a physical layer common  814 . The output of transistor  812  is connected to a 10,000 ohm resistor  816  that is connected to a physical layer common  814 . The transistor output also goes to inverter  820  that is also connected to physical layer common  814 . The output of the inverter  820  leads to one input of NAND gate  850 .  
         [0050]    A signal from the cable power regulator  830  is received at inverter  832  that is also connected to physical layer common  814 . The output of the inverter  832  is connected to the second input of NAND gate  850 . The output of NAND gate  850  is connected to the first input of XOR gate  852  and the first input of XOR gate  854 . The output of the inverter  832  is also connected to inverter  856  that is connected to a second input of XOR gate  852 . The output of XOR gate  852  is connected to the second input of XOR gate  854 . Gates  850  and  854  are also coupled to the physical layer common  814 .  
         [0051]    The output of XOR gate  854  is coupled with a first input of XOR gate  860  along with the input of 100,000 ohm resistor  862 . The second input of XOR gate  860  comes from the output of XOR  854  after having passed through  100   k  resistor  862 , inverter  864 , and inverter  866 . Inverter  864  is also coupled with a 1-microfarad capacitor  868  that is connected to physical layer common  814 . The output of XOR  860  goes to inverter  870  that is also connected to the physical layer common  814  and then to the physical layer  504  to cause a physical layer reset  880 .  
         [0052]    Thus in FIG. 8, the signal from the ASIC reset  802  comes from the controller chip in the printer or other appliance. When the signal goes to low that means the whole printer is getting reset. Such an example can be if the power plug is pulled from the socket. The other signal comes from the cable regulator enable  830 . When power at printer  100   a  drops the system enables secondary power from the bus to come in via cable  408 . With the use of XOR gate  860 , either of these conditions causes the circuit  404  to cause a physical layer reset  880  to be generated.  
         [0053]    This circuit  404  can monitor the status of the of an appliance&#39;s power. If that status changes, the circuit triggers a reset of the physical layer  504 . More specifically, this embodiment is configured for use with an appliance having internal motors such as a printer  100   a . This particular circuit monitors two conditions related to the appliance&#39;s power. The first condition is that of the motor control ASIC that monitors the power available to the printer&#39;s motor(s). If conditions occur that trigger an ASIC reset then the circuit  404  causes a physical layer reset. An example of such a condition can include but is not limited to a change in the motor supply power. The second condition is the status of the cable regulator. If primary power is lost and the physical layer  504  is switched to bus power then a physical layer reset  880  is triggered. Thus, in this configuration, which is just one of many possible embodiments, if either the printer is powered up or powered down, or if the bus cable power is activated then a physical layer reset is triggered. This functionality allows a reset to be generated when the printer power goes down and also allows a reset to be generated when the cable power comes on. In some exemplary embodiments, the cable power can be activated when the printer power has dropped below a normal operating range, but before the printer power falls all the way to zero. For example, a printer that normally operates at about 32 volts can lose motor function when the power drops below about 20 volts, and thus be non-functional. However, some of the circuitry can operate at these lower voltages and so may stay operational until the voltage falls to approximately zero. Thus, this configuration can allow a reset to be generated based on the cable power enable without the printer voltage having to fall to zero.  
         [0054]    In this example, the appliance can normally be powered around 32 volts, the circuit can cause a physical reset if the power drops below around 12 volts. Alternatively, it can also cause a reset if the monitored voltage goes from less than about 9 volts to more than about 30 volts. Those of skill in the art will recognize other satisfactory power supply parameters as well as other satisfactory embodiments.  
         [0055]    The physical layer reset will cause a bus or network reset that will cause all the appliances on the system to self-ID. If the circuit was triggered by a power down that appliance will self-ID to the network as being unavailable. The remaining appliances can use this information and not send data to the unavailable appliance.  
         [0056]    As shown in FIG. 8, the circuit is comprised of separate distinct components. Other satisfactory embodiments provide the circuit on an integrated circuit board fabricated from a semiconductor material. The functionality of the circuit can alternatively be achieved as an ASIC (application specific integrated circuit). The ASIC can be located on a die. Other exemplary embodiments combine the functionality of the described circuit with the IEEE 1394 chip. For example, both functionalities can be combined on a single die. This combined functionality can be located on the appliance, or as a self-contained freestanding unit, among others.  
         [0057]    The embodiments described above provide a dedicated circuit for each individual appliance connected to the system. Other exemplary embodiments can have fewer than all of the appliances equipped with the circuit. For example, connecting even one appliance on an IEEE 1394 network to a circuit as described above can be advantageous. It will be recognized by one of skill in the art that the exemplary embodiment described in FIG. 8 is but one satisfactory embodiment, and that many other satisfactory embodiments can be constructed.  
         [0058]    Exemplary Method  
         [0059]    [0059]FIG. 9 is a flow chart depicting the steps in one exemplary embodiment. The following method can be implemented in any suitable hardware, software, firmware, or combination thereof. Step  902  couples an electronic appliance to an IEEE 1394 compliant serial bus network. The electronic appliance can be any type of appliance suitable for use with such a network.  
         [0060]    Step  904  monitors a status of a power supply of the electronic appliance.  
         [0061]    Step  906  transmits a signal on the serial bus network when the status changes. FIG. 8 shows but one exemplary circuit that can be used to implement steps  904  and  906 . In one exemplary embodiment, the signal comprises a physical layer reset signal from the appliance. According to IEEE 1394 protocols, this signal can cause a network bus reset that requires each appliance on the network to self-ID. The self-ID can include a link layer status condition. An appliance that reports that its link layer cannot receive data and therefore the other appliances can be programmed to not send data to the appliance until it can report a functioning link layer.  
       CONCLUSION  
       [0062]    The described embodiments relate to a system that allows electronic devices or appliances to send data to one another. The described system can increase the efficiency of data transmission. Electronic devices can include computers, printers, digital cameras, and scanners among others. In one exemplary embodiment, the system may comprise an IEEE 1394 serial bus network. A bus is a transmission path on which signals are dropped off or picked up by electronic devices on the system. An IEEE 1394 serial bus is a bus complying with standards established by the Institute of Electrical and Electronics Engineers. The system can include various IEEE 1394 compliant appliances that can be connected to the IEEE 1394 serial bus. The system also includes one or more circuit(s) for the appliance(s). The circuit(s) monitors a status of the appliance(s) to improve system performance.  
         [0063]    The IEEE 1394 standard contains various protocols that require certain features of any appliance configured to the system. These features include IEEE 1394 compliant electrical devices that form an interface between the appliance and the serial bus. In some exemplary embodiments, these electrical devices comprise integrated circuit chips, though other suitable embodiments can be constructed. The electrical devices provide varying layers of functionality to the system. Two of the functional layers are termed the physical layer and the link layer.  
         [0064]    The IEEE 1394 protocols for the physical layer and the link layer allow the circuit(s) to increase the performance of the system. The circuits can monitor a status of the appliance that can affect the system. In some exemplary embodiments, the monitored status can be a power supply status of the appliance. If the circuit detects a change in the power supply status of the appliance, it can cause an IEEE 1394 physical layer chip coupled to the circuit to reset. According to IEEE 1394 protocols, specifically the IEEE 1394 compliant integrated circuits specifications, a physical layer reset will cause a system bus reset that causes each appliance on the system to provide a self-identification (self-ID).  
         [0065]    The self-ID data from each appliance includes a status report regarding the appliance&#39;s link layer functionality. The status report will indicate either that the link layer is active or inactive. In the case of an inactive link layer, the other appliances on the system will not send data to that appliance. This can prevent a functioning or active appliance from sending data repeatedly to a non-functioning or inactive appliance that cannot receive the data. Additionally, in the case of a power failure to an individual appliance, that appliance&#39;s physical layer can be switched to a secondary power supply provided by the system on IEEE 1394 compliant serial cables. This secondary power supply can allow data to flow through the inactive appliance&#39;s physical layer on a path from one active appliance to another.  
         [0066]    Although the invention has been described in language specific to structural features and/or methodological steps, it is understood that the invention defined in the appended claims is not necessarily limited to the specific features or steps described. Rather, the specific features and steps are disclosed as preferred forms of implementing the claimed invention.