Abstract:
In a data communication apparatus provided with first and second digital interfaces respectively connectable to first and second external devices, communication (including synchronous communication and asynchronous communication) is conducted between the first external device and the first digital interface. When connection between the second digital interface and the second external device is detected, priority is given to communication with the second external device connected to the second digital interface. Preferably, the data communication apparatus causes the first external device to recognize the new connection configuration. As a result, the data communication apparatus can rapidly conduct data communication with a prescribed device without imposing a large load on the network.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a data communication system, apparatus, and method, and more particularly, to a technique of communication of data via a digital interface. 
     2. Description of the Related Art 
     It has been the conventional practice to connect peripheral equipment such as a hard disk or a printer to a personal computer (hereinafter referred to as “PC”) via a digital interface (hereinafter referred to as “I/F”) such as an SCSI or an IDE, thereby conducting communication of digital information data with PC. 
     AV (audio-visual) devices such as a digital camera and a digital video camera so far not falling under peripheral equipment of a PC have now serve as input units to the PC as a result of progress made in this area. Various techniques are being developed for such input units, for example, entering moving images or a still image taken by any of these devices into a PC, processing and editing the image on the PC, and storing the resultant image in a hard disk or printing it out on a printer. 
     However, it has been difficult to send in a real-time manner digital data in a large quantity such as animation images from a digital video camera to a PC through a digital I/F such as an SCSI conventionally used for a hard disk or a printer, because of a low data transfer rate. Further, the conventional digital I/F, based on parallel communication, have large connectors and cables, are not suitable for an interface for a portable device requiring downsizing such as a digital camera and a digital video camera. In the conventional digital I/F, inconveniences have been pointed out in many aspects, including limitations of the connecting method, and complicated setting upon connecting. AV devices such as a digital camera and a digital video camera have therefore been connected to a PC via a digital I/F based on a technique different from that of the digital I/F such as an SCSI. 
     In a network in which a PC is connected to peripheral equipment and an AV device, when image information of the AV device is printed out, it has been necessary first to transfer image information via a digital I/F different from the conventional one, and further, to output from the PC to a printer via a conventional I/F. As a result, the AV device transmitting data in a large quantity to the PC poses a considerable load on the PC itself, and causes the network to be seriously crowded. Depending upon operation of the PC, it is affected by communication between other devices on the network, thus leading to a problem of making it impossible to normally print out the image information of the AV device. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to solve the above-described problems. 
     Another object of the invention is to achieve rapid data communication, in a data communication apparatus, with a prescribed device without applying a large load on the network. 
     As a preferred embodiment for such objects, the invention provides a data communication apparatus, comprising (a) first and second connecting means for connecting said apparatus to respective first and second external devices through respective first and second transmission lines, said first and second transmission lines transmitting digital data; (b) communication means for communications with the external device connected to said first or second connecting means; (c) detecting means which detects connection of the second external device to said second connecting means; and (d) control means for giving priority to communication between said communication means and the second external device connected to said second connecting means in response to the detection of said detecting means. 
     As another embodiment, the invention provides a data communication apparatus comprising (a) a first port connectable to a first data bus; (b) a second port connectable to a second data bus; (c) communication means for performing data communication with one of said first and second data buses through the corresponding first or second port; and (d) control means for causing a re-configuration of said first data bus in response to a connection of said second port to said second data bus. 
     As another embodiment, the invention provides a data communication apparatus, comprising (a) first and second communication means respectively communicable with first and second external devices; (b) power supply means which supplies power to said first and second communication means; (c) detecting means which detects a connection between said second communication means and the second external device; and (d) control means which controls said power supply means so as to change the power supplied to said first and second communication means in response to the detection of said detecting means. 
     As another embodiment, the invention provides a data communication apparatus, comprising (a) first communication means communicable with a first data bus; (b) second communication means communicable with a second data bus; (c) detecting means which detects the connection of an external device to said second communication means; and (d) control means which causes said first communication means to discontinue communication with said first data bus in response to the detection of said detecting means. 
     Another object of the invention is to achieve rapid data communication, in a data communication method, with a prescribed device without applying a large load on the network. 
     As a preferred embodiment for such an object, the invention provides a data communication system, comprising (a) first and second connecting means for connecting said apparatus to respective first and second external devices through respective first and second transmission lines, said first and second transmission lines transmitting digital data; (b) communication means for communicating with the external device which is currently connected to said first or second connecting means; (c) detecting means which detects the connection of the second external device to said second connecting means; and (d) control means which gives priority to communication between the communication means and the second external device connected to said second connecting means when said detecting means detects connection of said second external device to said second connecting means. 
     As another embodiment, the invention provides a data communication system, comprising (a) a first port connectable to a first data bus; (b) a second port connectable to a second data bus; (c) communication means for performing data communication with one of the first and second data buses through one of said first and second ports identified as being valid; and (d) control means for causing said first data bus to recognize data bus configuration in response to the connection of said second port to said second data bus. 
     As another embodiment, the invention provides a data communication system, comprising (a) first and second communication means respectively communicable with first and second external devices; (b) power supply means for supplying power to said first and second communication means; (c) detecting means which detects the connection of said second communication means to the second external device; and (d) control means which controls said power supply means so as to change power supplied to said first and second communication means in response to said detecting means detecting the connection of said second communication means to the second external device. 
     As a further embodiment, the invention provides a data communication system, comprising (a) first communication means communicable with a first data bus; (b) second communication means communicable with a second data bus; (c) detecting means which detects the connection of an external device to said second connecting means; and (d) control means which controls said first communication means so as to discontinue communication with said first data bus in response to said detecting means detecting the connection of the external device to said second connecting means. 
     Another object of the invention is to achieve rapid data communication, in a data communication system, with a prescribed device without applying a large load on the network. 
     As a preferred embodiment for such an object, the invention provides a method of data communication, comprising the steps of: (a) providing first and second communication interfaces for communicating with respective first and second external devices over respective first and second transmission lines, said first and second transmission lines transmitting digital data; (b) detecting a connection of the second external device to said second interface; and (c) giving priority to communication with the second external device connected to said second interface in response to the result of detection obtained from said detecting step. 
     As another embodiment, the invention provides a method of data communication, comprising (a) a setting step of selecting as valid one of a first port connectable to a first data bus and a second port connectable to a second data bus; (b) a communicating step of conducting data communication via the first or second data bus selected as valid in said setting step; and (c) a control step of causing said first data bus to recognize a new bus configuration in response to a connection of said second port to the second data bus. 
     As another embodiment, the invention provides a method of data communication, comprising (a) a power supplying step of supplying power to first and second digital interfaces communicable with respective first and second external devices; (b) a detecting step of detecting a connection of said second digital interface to the second external device; and (c) a control step of changing power supplied to said first and second digital interfaces in response to the detection obtained from said detecting step. 
     As a further embodiment, the invention provides a method of data communication, comprising (a) a communicating step of conducting communication with a first data bus via a first digital interface; (b) a detecting step of detecting the connection of an external device to a second digital interface communicable with a second data bus; and (c) a control step of controlling said first digital interface so as to discontinue communication with said first data bus in response to the result of detection obtained from said detecting step. 
     Still other objects of the present invention, and the advantages thereof, will become fully apparent from the following detailed description of the embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram illustrating a configuration of a printer  101  in a first embodiment of the invention; 
     FIG. 2 illustrates a typical network using the printer  101 ; 
     FIG. 3 is a flowchart illustrating operations of the printer  101  upon connection to the network shown in FIG.  2 ; 
     FIG. 4 is a block diagram illustrating a system configured by connecting a digital camera  22  to a connector port ( 3 )  107  of the printer  101 ; 
     FIG. 5 is a block diagram illustrating a system configured by connecting a digital camera  500  to a connector port ( 3 )  107  of the printer  101 ; 
     FIG. 6 illustrates a network built by the use of a digital I/F in conformity to an IEEE1394 serial bus; and 
     FIG. 7 illustrates components of the IEEE1394 serial bus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention will now be described in detail hereinafter with reference to the accompanying drawings. 
     1. First Embodiment 
     FIG. 1 is a block diagram illustrating a configuration of a printer in a first embodiment of the present invention. The printer shown in FIG. 1 is configured to be connected to other digital devices by the use of a digital I/F conforming to the IEEE1394-1995 high-performance serial bus standard (hereinafter referred to as “IEEE1394”). The IEEE1394 serial bus will be briefly described below. Details of the IEEE1394 are described in the “IEEE Standard for a High Performance Serial Bus”, published by the Institute of Electrical and Electronics Engineers, Inc., 345 East 47th Street, New York, N.Y. 10017, USA, Aug. 30, 1996. 
     A typical network system built by the use of a digital I/F conforming to the IEEE1394 Serial Bus Standard is illustrated in FIG.  6 . Each of devices A, B, C, D, E, F, G and H of this system is provided with an IEEE1394 I/F, and A and B, A and C, B and D, D and E, C and F, C and G, and C and H are connected with twist pair cables of IEEE1394 serial bus. Examples of these devices A to H include a digital VTR, a DVD, a digital camera, a hard disk, and a monitor. 
     These devices may be connected by the daisy chain technique and the node technique in mixture, thus permitting connection with high flexibility. 
     Each device has its own ID information, and the devices form a network within a range of connection with 1394 serial buses through mutual recognition. By only sequentially connecting these digital devices via IEEE1394 I/Fs, the individual devices perform relay of transferred data, thus forming a network as a whole. The IEEE1394 has a plug and play function, which permits automatic recognition of the devices connected to the network without turning off the power supply for the entire network. 
     When all the devices are deleted from the network or a new device is added, for example, in an IEEE1394 network as shown in FIG. 6, the network can perform an operation of recognizing the new network after automatic resetting, i.e., after resetting the existing network configuration. Because of this function, the IEEE1394 network can always recognize a change in connection configuration of the network. 
     The IEEE1394 network is provided with three data transfer rates 100, 200 and 400 Mbps, and devices having higher transfer rates support lower transfer rates to ensure compatibility. 
     There are available two data transfer modes for the network shown in FIG.  6 : an asynchronous transfer mode for transferring data asynchronously transferred from time to time such as a control signal (asynchronous data: hereinafter referred to as “async-data”) and an isochronous transfer mode for transferring data to be continuously transferred at a constant data rate such as video data and audio data (isochronous data: hereinafter referred to as “iso-data”). These async-data and iso-data are transferred in mixture within a cycle in the order of iso-data and then async-data following a cycle start packet (CSP) indicating the start of a cycle within a communication cycle (usually 125 m per cycle). A transfer band of iso-data is ensured within each cycle. 
     Now, protocol layers of the IEEE1394 serial bus are shown in FIG.  7 . 
     The IEEE1394 serial bus as a whole is composed of a plurality of layers. In FIG. 7,  801  is a serial bus cable conforming to the IEEE1394 Serial Bus Standard, which is connected to a physical layer  803  and a link layer  804  contained in a hardware section via a connector port  802  of the IEEE1394 I/F. 
     The hardware section is a substantial portion of an interface chip. The physical layer  803  conducts coding and decoding of an input/output signal and control of the connector port  802 , and the link layer  804  performs packet transfer and cycle time control. 
     A transaction layer  805  of a firmware section controls data to be transferred (transacted), and issues commands such as Read and Write. A serial bus management layer  806  manages the status of connection of connected devices and ID information (node ID), and control the network configuration. 
     The components up to the hardware section and the firmware section are included in the substantial configuration of the IEEE1394 serial bus. 
     An application layer  807  of a software section varies with the software program used and controls how to conduct input/output of data for transfer on the IEEE1394 serial bus: for example, moving images are controlled by a protocol such as an AV protocol. 
     Each of the devices (nodes) connected on the IEEE1394 serial bus is assigned ID information, i.e., a node ID, by means of which the network configuration can be recognized. 
     When a change occurs in the network configuration, for example, when a change occurs on the network as a result of an increase or a decrease in the number of nodes caused by pullout of a node or ON/OFF of the power supply, and it is necessary to recognize a new network configuration, the node which detects the change transmits a bus reset signal on the bus to enter into a mode for recognizing the new network configuration. The detection of such a change is accomplished by detecting a change in bias voltage in the IEEE1394 connector port  802  and the physical layer  803 . 
     A bus reset signal issued by a node is entered into the physical layer  803  of each node. The physical layer  803  of each node communicates the occurrence of a bus reset to the link layer  804 , and at the same time, transfers the bus reset signal to other nodes. Finally, after all the nodes have detected the bus reset signal, the bus reset (i.e., recognition processing of the network configuration) is started. 
     Bus reset can be started by hardware detection caused by pullout of the cable or an abnormality in the network as described above, or by protocol&#39;s issuing a command directly to the physical layer through host control. 
     Upon start of bus reset, data transfer is temporarily interrupted, data transfer being in standby during this interruption, and after the end of this interruption, restarted under the new network configuration. 
     Now, the configuration of the printer shown in FIG. 1 will be described below. 
     In FIG. 1,  101  is a printer;  102  is a printer system control unit for controlling the entire printer  101 ;  103  is an IEEE1394 I/F section (a);  104  is an IEEE1394 I/F section (b);  105  is a connector port ( 1 ) for the I/F section (a)  103 ;  106  is a connector port ( 2 ) for the I/F section (a)  103 ;  107  is a connector port ( 3 ) for the I/F section (b)  104 ;  108  is an I/F power supply for supplying power to the I/F sections ( 103  and  104 );  109  is a switch for disconnecting/supplying I/F power  108  to the I/F sections ( 103  and  104 ) as required;  110  is a gate section for selecting the I/F sections ( 103  and  104 ) capable of acting in linkage with the printer system control section  102 . 
     An operation panel  111  for setting functions for the printer  101  and a paper feed port  112  are arranged on the front of the printer  101 . The port ( 3 )  107  is also arranged on the front of the printer  101  as shown in FIG.  1 . 
     A six-pin cable including a power supply line can be connected to the port ( 1 )  105  and the port ( 2 )  106 , with a maximum transfer data rate of 400 Mbps, whereas a four-pin cable can be connected to the port ( 3 )  107 , with a maximum transfer data rate of 100 Mbps. 
     The foregoing IEEE1394 I/F sections (a)  103  and (b)  104  form a configuration conforming to the IEEE1394-1995 Serial Bus Standard. 
     Now, operations of the printer  101  in the first embodiment of the invention, having the configuration as described above, will be described below. 
     The printer  101  shown in FIG. 1 is usually set so as to supply power from the I/F power supply  108  to the I/F section (a)  103 . A network can be built by connecting directly or indirectly the I/F section (a)  103  to the connector ports ( 1 )  105  and ( 2 )  106  and a digital device having the same IEEE1394 I/F. When the I/F section (a)  103  is valid, the printer  101  serves as a network printer, and can print an output from another digital device in the network. 
     When the setting is made so as to supply power from the I/F power supply to the I/F section (a)  103  as described above, the switch  109  for selecting a supply source of power and the gate circuit  110  for selecting a communication destination of the printer system control section  102  select the I/F section (a)  103  side. However, the I/F power supply  108  supplies the minimum bias so as to permit detection of the connection of the connector port ( 3 )  107  of the I/F section (b)  104  to the other device. 
     When a digital device having an IEEE1394 I/F is connected to the connector port ( 3 )  107  of the I/F section (b)  104 , the physical layer of the IEEE1394 I/F section (b)  104  detects the connection. This result of detection is sent to the printer system control section  102  which instructs the gate circuit  110  and the switch  109  to switch over the interface. In compliance with this instruction, the gate circuit  110  releases the connection with the I/F section (a)  103 , and performs switching so that connection with the I/F section (b)  104  becomes valid. The switch  109  also switches power supply from the I/F power supply from the I/F section (a)  103  to the I/F section (b)  104 . In other words, the printer  101  can conduct communication only with the device connected to the I/F section (b)  104 . When the I/F section (b)  104  is valid, the printer  101  serves as a direct printer. 
     While the I/F section (b)  104  detects insertion/removal of the connector by a method conforming to the IEEE1394 Standard, means for detecting physical insertion/removal of the connector may be provided in the connector port ( 3 )  107  itself, thereby detecting the same. 
     When connection of any other device is detected by the I/F section (b)  104 , as described above, the printer  101  temporarily interrupts communication with the individual devices connected to the I/F section (a)  103  or finishes completely, and starts preferentially communication with the digital devices connected to the I/F section (b)  104 . 
     When power is supplied to the I/F section (b)  104 , the setting is such that the printer  101  disconnects supply of power to the I/F section (a)  103 . As a result, each of the digital devices connected to the I/F section (a)  103  and forming the network deems power of the printer  101  itself to be turned off (detected), and conducts resetting to build again a new network in a configuration except for the printer  101 . In this embodiment, the foregoing bus reset is accomplished by a method conforming to the IEEE1394 Standard. Upon detection of connection to the I/F section (b)  104 , it is also possible that the printer  101  itself transmits a signal requiring bus reset on the network connected to the I/F section (a)  103 . 
     The connector port ( 3 )  107  of the I/F section (b)  104  is provided at a position permitting insertion and removal from the front or front side, i.e., from the front of the printer  101  so as to enable the user to easily conduct connection with digital devices allowing temporary connection as in a digital camera or a digital video camera. In this embodiment, the face containing the paper feed port  112  and the operation panel  111  serves as the front (front face). 
     As described above, the printer  101  is usually set so as to serve as a network printer, and may be designed so as to serve as a direct printer when temporarily connectable digital devices such as a digital camera or a digital video camera. 
     FIG. 2 illustrates a typical network comprising the printer  101  and a plurality of digital devices. 
     In FIG. 2, the printer  101  is connected to the PC  23  and the scanner  24  (the other digital devices) via the IEEE1394 I/F to form a network. In this configuration, a digital camera  22  having the IEEE1394 I/F can be at any time connected to the connector port ( 3 )  107  provided on the front of the printer  101 . 
     When the digital camera  22  is connected to the printer  101 , the printer  101  detects this connection, finishes communication with the network built with the PC  23  and the scanner  24  as described above, and begins communication only with the digital camera  22 . As a result, image data from the digital camera  22  can be directly communicated with the printer  101  for printing, so that it is not necessary to print via the PC  23  as before. Since the digital camera  22  can use the printer  101  exclusively, it is possible to perform rapid communication of image data in a very large amount without being affected by the other digital devices. 
     While the network shown in FIG. 2 is composed of the PC  23  and the scanner, it is naturally possible to further connect a plurality of another digital devices. 
     FIG. 3 is a flowchart illustrating operations of the printer  101  in the configuration of the network shown in FIG.  2 . 
     In step S 1 , the printer  101  forms a network with a plurality of digital devices (for example, a PC  23  and scanner  24 ) connected to the ports  105  and  106 , with a valid I/F section (a)  103  shown in FIG. 1, and performs communication with the individual digital devices via the I/F section (a)  103 . At this point, a gate circuit  110  is set so that the individual digital devices connected to the I/F section (a)  103  can communicate with the printer system section  102 , and connection with the I/F section (b)  104  is open. An I/F power supply  108  supplies power to the I/F section (a)  103  side. 
     In step S 2 , the I/F section (b)  104  detects whether or not digital devices such as a digital camera  22  have been connected to the connector port ( 3 )  107 . When connection is detected, processing is transferred to step S 3 . When connection is not detected, the gate circuit  110  keeps connection with the I/F section (a)  103  so as to allow communication with the I/F section (a)  103  made valid. 
     In step S 3 , the gate section  110  opens (invalidates) the connection between the I/F section (a)  103  and the printer system section  2  with a view to preferentially communicating with the digital camera  22  connected to the I/F section (b)  104  in response to the result of detection in step S 2 . As a result, the individual devices connected to the I/F section (a)  103  deems power for the printer  101  to be turned off, and rebuilds the network except for the printer  101  by a method prescribed in the IEEE1394 Standard. 
     In step S 4 , the gate section  110 , after releasing connection between the I/F section (a)  103  and the printer system section  102 , validates connection between the I/F section (b)  104  and the printer system control section  102 . 
     In step S 5 , the I/F power supply  108  supplies power necessary for the I/F section (b) to the same. As a result, the I/F section (b)  104  becomes communicable, and begins communication with the digital camera  22 . 
     In step S 6 , the printer  101  and/or the digital camera  22  may perform communication with the interfaces of the individual digital devices, and begin bus reset, i.e., recognition of the new network, in accordance with the IEEE1394 Standard. As a result of this bus reset, node IDs conforming to the IEEE1394 Standard are set for the printer  101  and the digital camera  22  (step S 7 ). 
     Upon completion of operations up to step S 7 , data communication conforming to a prescribed communication protocol is made possible on the IEEE1394 serial bus between the digital camera and the printer  101 . It is therefore possible to start printing out an image data taken by the digital camera  22  on the printer  101  (step S 8 ). This cycle of operations is repeated until the end of communication (step S 9 ). 
     As a result of these operations in the steps as described above, the digital camera  22  can retain the printer  101  in the network, thus permitting one-to-one communication. 
     FIG. 4 is a block diagram illustrating in detail a system built by connecting the digital camera  22  to the connector port ( 3 )  107  of the printer  101 . In FIG. 4, the same components as in FIG. 1 are assigned the same reference numerals. 
     In FIG. 4,  22  is the digital camera;  101  is the printer;  401  is an image sensing section for sensing an object to be photographed;  402  is an image processing section;  403  is a D/A converter;  404  is an EVF (Electric View Finder) displaying an image of the shot object;  405  is a compression/extension section;  406  is a recording/reproducing section recording and reproducing the image data;  407  is a memory recording the image data;  408  is a system controller which controls the digital camera  22 ;  409  is an operating section; and  410  is a 1394 I/F section mounted on the digital camera  22 . 
     Also in FIG. 4,  104  is the 1394 I/F section (b) connected to the 1394 I/F section  410  of the digital device, i.e., the digital camera  22  via a 1394 serial bus cable  411  of a four-pin terminal;  103  is the 1394 I/F section (a) connected to the plurality of digital devices via a six-pin terminal cable  418  having a maximum transfer rate different from that of the four-pin terminal;  110  is a gate section for selecting and switching any of the I/F sections  102  and  103 ;  412  is an extension section;  413  is a memory used upon carrying out an operation of forming a print image;  414  is a printer head performing printing;  415  is a print head driver;  416  is a connector detecting section which detects insertion of the connector into the connector port ( 3 )  107  of the I/F section (b)  104 ; and  417  is the printer controller which controls operations of the entire printer  101 . In the compression/extension section  405  and the extension section  412 , a still image is compressed and codified by the use, for example, of the JPEG technique. 
     Now, operations of the printer  101  and the digital camera  22  connected as shown in FIG. 4 will be described. 
     First, the processing effected upon recording image data of an image taken by the digital camera  22  will be described. The image data of the object taken and generated in the image sensing section  401  are A/D-converted by the image processing section  402 , and converted into a standard television signal based on the NTSC technique or the like. An output of the image processing section  402  is converted back into an analog signal by the D/A converter  403  in the form of a shot image, and displayed on the EVF  404 . The other output is subjected to a prescribed compression-coding processing based on the JPEG technique or the like in the compression/extension section  405 , and recorded in the memory  407  by means of the recording/reproducing section  406 . 
     When reproducing the image data recorded in the memory  407 , the recording/reproducing section  406  reads out a desired image from the memory  407  in compliance with an instruction (play command) of the operating section  409 . At this point, the selected desired image is controlled and displayed by the system controller  408  on the basis of the information entered from the operating section  409  (image specifying command). More specifically, the still image data reproduced from the memory  401  are extended in the compression/extension section  405 , and displayed on the EVF via the image processing section  402  and the D/A converter  403 . 
     The user can cause direct printout of desired image data onto the printer  101  from the camera operating section  409 . The system controller  408  displays the desired image data read out from the memory  407  on the EVF  404  in response to an output from the operating section  409 , and at the same time, performs control so as to send the same to the I/F section (b)  104  of the digital camera  22 . At this point, the image data reproduced by the recording/reproducing section  406  are compressed by the JPEG technique. The image data sent to the I/F section (b)  104  of the digital camera  22  is transferred to the I/F section (a)  103  via the cable  411 . 
     Transfer of the image data is accomplished through isochronous transfer or asynchronous transfer conforming to the IEEE1394 Standard. 
     The printer  101  usually forms a network together with a plurality of digital devices connected to the I/F section (a)  103 , and is set so as to permit communication with the individual devices. When the digital camera  22  as described above is connected to the I/F section (b)  104 , the printer controller  417  of the printer  101  controls the gate section  110  and the I/F power supply  108  in response to an output from the connector detecting section  416  so that communication of only the digital device connected to the I/F section (b)  104 , i.e., with the digital camera  22  becomes valid. 
     The still image data transferred from the digital camera  22  to the printer  101  are entered via the gate section  110  into the extension section  412 . In the extension section  412 , the image data are extended by the use of a JPEG extension program stored in the ROM in the circuit. The extended image data are formed into a printer image suitable for the printer  101  by means of the memory  413 , and printed out via the printer head  414 . The processing of the printer  101  as described above is controlled by the printer controller  417 . 
     As described above, the printer  101  automatically finishes communication with the I/F section (a)  103  by only connecting the digital camera  22  to the I/F section (b)  104  of the printer  101 , and starts communication only with the digital camera connected to the I/F section (b)  104 . As a result, it is possible to communicate directly with the printer  101  and conduct printing of the image data from the digital camera  22  without passing through a computer or the like. Since the digital camera  22  can use the printer at this point exclusively, it is possible to accomplish communication of data in a large quantity (such as image data) rapidly without being affected by the other digital devices. 
     The data bus on the I/F section (a)  103  disconnected from the printer  101  can separately perform communication of 400 Mbps, and the data transfer rate is not limited to 100 Mbps by the presence of a four-pin connector connected to the I/F section (b)  104 . 
     2. Second Embodiment 
     In a second embodiment of the invention, a configuration in which a digital VTR is connected to the printer  101  shown in FIG. 1 will now be described. In FIG. 5, the same components as in FIG. 1 are assigned the same reference numerals. 
     FIG. 5 is a block diagram illustrating in detail a configuration in which the digital VTR  500  is connected to the printer  101  described in the first embodiment. As in the first embodiment, the printer  101  and the digital VTR  500  have a digital interface conforming to the IEEE1394 Standard. 
     In FIG. 5,  500  is a digital VTR;  101  is the printer;  501  is a magnetic tape;  502  is a magnetic head performing recording/reproducing on the magnetic tape;  503  is an operating section which enters operational instructions (play, external output, etc.) for the digital VTR  500 ;  504  is a system controller which controls the operations of the digital VTR  500 ;  505  is a reproducing section which reproduces compressed image data recorded on the magnetic tape with the use of the head  502 ;  506  is an extension section which extends compressed and recorded image data;  507  is a D/A converter;  508  is a display section displaying image data reproduced from the magnetic tape  501  by means of an EVF (Electric View Finder);  509  is an output terminal outputting an image signal of the digital VTR  500 ;  510  is a memory storing an output from the extension section  506 ; and  511  is a 1394 serial bus I/F section of the digital VTR  500 . 
     Also in FIG. 5,  104  is a 1394 I/F section (b) connected to the 1394 I/F section  511  of the digital device, i.e., the digital VTR  500  via a four-pin terminal 1394 serial bus cable  512 ;  103  is a 1394 I/F section (a) connected to a plurality of digital devices via a six-pin terminal cable  513  having a maximum transfer rate different from that of the cable  512 ;  110  is a gate section which selects and switches the I/F sections  103  and  104 ;  514  is a memory used when forming a printed image;  515  is a printer head printing an image onto paper;  516  is a print head driver;  517  is a connector detecting section which detects insertion of the connector into the connector port ( 3 )  107  of the I/F section (b)  104 ; and  518  is a printer controller which controls operations of the entire printer  101 . 
     Now, operations of the printer  101  and the digital VTR  500  connected as shown in FIG. 5 will be described below. In FIG. 5, the digital VTR  500  is connected directly to the printer  101  as in the case of the digital camera  22  shown in FIG.  4 . 
     As the reproducing operation, the digital VTR  500  reproduces desired image data from among compressed image data recorded on the magnetic tape  501  by means of the magnetic head  502 . The desired image data are selected by the system controller  504  which controls the magnetic tape  501  and the magnetic head  502  on the basis of information entered from the operating section  503  (image specifying command). The image data thus reproduced are compressed and coded by a prescribed compression method based on DCT (Discrete Cosine Transformation) and VLC (Variable Length coding). The digital VTR  500  extends the same in the extension section  506 . The extended image data may be displayed on the EVF  508  via the D/A converter or an image signal may be issued from an external output terminal  509  to an external monitor. 
     Or, the user may put out the image data recorded in the digital VTR directly onto the printer  101 . In this case, the system controller  504  performs control so as to extend an output of the compressed image data from the reproducing section  505  in the extension section  506 , once storing the same in the memory  510 , and then send the same to the I/F section  511 . 
     The image data sent to the I/F section  511  are packetized by a method conforming to the IEEE1394 Standard, and transferred via the cable  512  to the I/F section (b) of the printer  101 . Transfer of the image data between the foregoing I/F section  511  and the I/F section (b)  104  is accomplished by isochronous transfer or asynchronous transfer conforming to the IEEE1394 Standard. 
     As in the first embodiment, the printer  101  usually forms a network together with a plurality of digital devices connected to the I/F section (a)  103  and is set so as to permit communication with the individual digital devices. When the digital VTR  500  as described above is connected to the I/F section (b)  104 , the printer controller  504  of the printer  101  controls the gate section  110  and the I/F power supply  108  in response to an output from the connector detecting section  517 , so that communication only with the digital device connected to the I/F section (b)  104  is permitted, i.e., only the digital VTR is valid. 
     The image data transferred to the printer  101  are formed into a printed image via the gate section  110  in the memory  514 , and printed by the printer head  515 . The printer controller  518  controls switching of the connecting destination of the gate section  110  and write/read of the memory  514  on the basis of information from the connector detecting section  517 . The printer controller  518  controls operation of the driver  112  driving the printer head  109  and a paper feed mechanism not shown. 
     As described above, the printer  101  of the second embodiment, as in the first embodiment, automatically finishes communication with the I/F section (a)  511  and starts communication with only the digital VTR  500  connected to the I/F section (b)  104  only by connecting the digital VTR  500  to the I/F section (b)  104  of the printer  101 . As a result, it is possible to communicate the image data from the digital VTR  500  directly to the printer  101  for printing without passing through a computer or the like. Because the digital VTR  500  can employ the printer exclusively, communication of data in a large quantity (such as image data) can be accomplished rapidly without being affected by other digital devices. 
     In this embodiment, as in the first embodiment, the data transfer rate of the network disconnected from the I/F section (a)  103  is not limited by the data transfer rate of the I/F section (b)  104 . 
     In this embodiment, as in the first embodiment, furthermore, the printer  101  forms a network together with a plurality of digital devices, and apart from the I/F section (a)  103 , the I/F section (b)  104  communicable directly with an output device such as a digital camera  22  may be provided on the front or the side front of the printer  101 , thereby permitting easy connection of a portable device such as a digital camera. In the first and second embodiments, the I/F sections (a) and (b)  103  and  104  use an interface conforming to the IEEE1394 Standard. The invention is not however limited to this, but an interface for radio communication based on the IrDA technique may be used for the I/F section (b)  104 . 
     Various variations are possible without deviating from the spirit of the present invention or from the main features thereof. For example, while the embodiments have been described with a digital camera  22  and a digital VTR  500  as a device exclusively operating the printer  101 , the invention is applicable also to such digital devices as a DVD (Digital Video Disc) player, an MD (Mini Disc) player and PC (Personal Computer), not limiting to the digital devices mentioned above. 
     In the embodiments of the invention, the printer  101  has been described as a digital device exclusively used by the digital camera  22  or the digital VTR  500 . It is not however limited to the printer  101 , but the invention is applicable also to a PC, a hard disk or a scanner. The embodiments shown above are therefore only examples, and should not be construed as limiting. 
     The scope of the present invention is defined by the claims, and is not constrained at all by the text of the specification. All variants and modifications falling under the scope of claims are with the scope of the present invention.