Image information processing system
FIELD OF THE INVENTION 
     The present invention relates to an image information processing system which comprises an image reading unit, a recording unit, a communication unit, etc. as in a facsimile apparatus, and to which is connected a personal computer, etc. to permit any desired image information processing. 
     DESCRIPTION OF THE PRIOR ART 
     In recent years, there has been increased the need of transmitting and editing image data consisted of figures, characters, etc. Heretofore a facsimile apparatus has been employed as an apparatus for transmitting image information. The apparatus of this kind is, however, so designed as only to simply read the image of an original document for transmitting the read image to another facsimile as well as to receive image information sent from another facsimile for recording the same. 
     The user who employs a facsimile has a demand of, for example, extracting and transmitting the required area of an original document, transmitting the image of an original document with a particular area being masked, or transmitting the image of an original document added with particular patterns, characters, etc. In such a case, the document must be reedited using paste and scissors and then copied to prepare a document susceptible of transmission. 
     In general, offices or business premises must preserve a number of documents, which requires a very large preservation space and which makes very troublesome the retrieval operation for taking out a part thereof as well as the operation for putting in order those documents. If those documents are recorded as image data in any of various storage mediums, it would be possible to make small the space for preserving the documents and to simply perform retrieval and putting in order thereof using a computer or the like. However, the apparatus for use in reading image data from a document, etc. with high accuracy and applying the data to a computer as well as in recording the image data stored in the computer on a paper sheet with high quality, is usually large in size and very expensive, and it has only a function of reading and recording. 
     A facsimile apparatus is capable of reading, recording and communicating image data with relatively high accuracy. Therefore, if the conventional facsimile apparatus is modified to be connectable with a personal computer, etc. to permit transfer of image data between the facsimile and the computer, it would be possible to process the data in various manners and store the same on the computer side, to return the data back to the facsimile for recording, and to transmit the data from one facsimile to another facsimile apparatus, as required. 
     In the meantime, when connecting a computer or the like to a facsimile apparatus, the configuration of an interface unit is very important from the following reasons. 
     Firstly, since the image data read out of a document has a very large quantity of data, it takes a longer time period to transfer the data between the reading/recording apparatus and the computer if the data transmission speed is low. This results in a longer processing time and, when the reading/recording apparatus is combined with the ordinary facsimile, the transmitter side must wait for a long time frequently even upon receiving a reception request from another facsimile, because the apparatus is under operation. In case of transmitting data at a high speed, there has been heretofore used a parallel data transmission system (e.g., centronics interface). 
     Secondly, it is preferable to reduce the number of data lines for an interface and lines for a control signal, and hence to reduce the volume (or weight) of connection cables. In other words, with decreasing the number of lines, the cost of the connection cables themselves is lowered when the apparatus is interconnected through a long distance, and the presence of the connection cables becomes less obstructive when facsimiles, computers, etc. are used independently from each other or in combination with other equipment connectable thereto, and when they are moved as required. In such a case, there has been heretofore employed a serial data transmission system e.g., RS-232C interface. 
     However, the serial data transmission system is complicated and expensive in its circuit configuration and has a relatively low transmission speed, while the parallel data transmission system requires a very large number of data lines and control signal lines. 
     SUMMARY OF THE INVENTION 
     The present invention has for its first object to connect an information processor such as a computer with a facsimile apparatus, and for its second object to both make an inexpensive interface unit for use in connecting therebetween and connection cables, and achieve high-speed data transmission through the interface unit. 
     The parallel data transmission system is more fit for transmitting data at a high speed. When an image data reading/recording apparatus such as a facsimile apparatus is connected to an information processor such as a personal computer, an interface is required to perform the function of transmitting data from the image data reading/recording apparatus to the information processor as well as a function of transmitting data from the information processor to the image data reading/recording apparatus. Accordingly, in case of using, for example, two sets of centronics interfaces, there are needed 16 data lines per se and at least about 6 control signal lines in addition to the former, so that the cables necessary for connecting those lines become very large in the volume and very high in the cost. 
     Now considering operation of the interface unit from the viewpoint of time, there is practicably no possibility that the operation for inputting data into the image data reading/recording apparatus from the exterior is run simultaneously with the operation for outputting data to the exterior. The number of data lines is thus decreased to half, if those lines are formed as bidirectional lines to be commonly used for inputting and outputting. As to the control signal lines, since the data sending signal (SEND), for example, is a signal which is to be passed from the transmission side to the reception side and which is never issued from the reception side, it is also possible to commonly use the same lines as data sending lines for two apparatus on both sides. 
     When both the data lines and the control signal lines are formed of bidirectional lines in this way, the problem is in such a possibility that the apparatus on both sides may output respective signals on the same single line simultaneously. To avoid this, either one of the apparatus interconnected to each other may be designed to control the direction of a signal to be passed through the signal lines. When connecting an image data reading/recording apparatus to a personal computer or the like, if the image data reading/recording apparatus is designed to control the direction of signal, transmission the personal computer encounters a large limitation in preparing the program thereof, because it can not start to transmit data until the switching timing of the direction control signal and the processing program for the personal computer must be prepared in accordance with that timing. Therefore, it is preferable to control the direction of a signal on the interface line in accordance with a signal from an external apparatus (such as a personal computer which is connected to the interface. 
     Other objects and features, together with the foregoing, are attained in the embodiment described in the following description and illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of showing an image information processing system according to one embodiment of the present invention; 
     FIG. 2 is a block diagram showing the system configuration of FIG. 1; 
     FIG. 3 is a detailed block diagram showing the configuration of a part of both computer interface IFF and input/output interface IFP shown in FIG. 2; 
     FIGS. 4a and 4b are flowcharts showing schematic operation of a system control unit SCU; 
     FIG. 5 is a flowchart showing schematic operation of a personal computer 1; and 
     FIGS. 6a and 6b are timing charts showing examples of signal timing in an interface circuit. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIG. 1, a personal computer 1 is connected to a facsimile apparatus 10 through an interface connection cable CAB in the illustrated embodiment. The facsimile apparatus 10 is equipped with a telephone set FTE which is connected to the public telephone line. 
     FIG. 2 shows the schematic configuration of the system illustrated in FIG. 1 in the form of a block diagram. Now referring to FIG. 2, the personal computer 1 comprises a central processing unit CPU, an input/output interface IFP, a keyboard KEY, a display CRT and external storage units FD1, FD2. 
     The facsimile apparatus 10 is composed of, from the viewpoint of its function, a network control unit NCU for controlling connection with the communication line, modulation/demodulation units (modems; LSM, HSM, FSK) for making conversion between an image signal and a communication signal, a data compression/reproduction unit DCR for compressing and coding image data and for reproducing image data from the compressed and coded data, a read/write buffer RWB for temporarily storing image data therein, a scanner ISA for reading image data of an original document, a plotter REC for hard-copying image data on a recording paper sheet, a system control unit SCU for controlling operation of the entire facsimile, and various interfaces. The respective functional blocks are connected to the system control unit SCU through the corresponding interface circuits. 
     The signal from the telephone line is provided via the network control unit NCU to a data switch unit DSU by which it is appropriately allocated to the modems LSM, HSM, FSK. Image information out of the demodulated signal is passed through the data compression/reproduction unit DCR and the read/write buffer RWB to drive a plotter driver WE, so that the plotter REC reproduces and records the image in the normal facsimile operation. In a transmission mode, the image signal processed by a video processor VPU is provided via the read/write buffer RWB to the DCR for compression, and thereafter applied to the modulation/demodulation units FSK, HSM, LSM. 
     A computer interface circuit IFF is connected to a bus line of the system control unit SCU, and the cable CAB connected in turn to the computer interface circuit is connected to the input/output interface circuit IFP of the personal computer 1. 
     FIG. 3 shows in detail a part of both the computer interface circuit IFF equipped on the facsimile side and the input/output interface circuit IFP equipped on the personal computer side. Incidentally, those symbols in the figure which are given with overlines mean that the corresponding signals become effective when their signal levels assume a low level L. 
     Description will now be made by referring to FIG. 3. In this embodiment, the interface cable CAB comprises 13 signal lines and a not shown earth line. The signal lines consist of 8 data lines for transferring parallel data of 8-bit and 5 control signal lines L1, L2, L3, L4 and L5. Referring first to the input/output interface circuit IFP equipped on the side of the personal computer 1, bidirectional gate circuits GA3 and GA4 with three state outputs are connected to 3 control signal lines L1, L2, L3 and 8 data lines DB0-DB7, respectively. 
     The control signal line L1 is a line which allows a single unidirectional signal ONLINE to pass therethrough from the facsimile 10 side to the personal computer 1 side, and another control signal line L2 is a line which allows a single unidirectional signal FAX/Input-Output to pass therethrough from the personal computer 1 side to the facsimile 10 side. The remaining control signal lines L3, L4 and L5 are formed as bidirectional lines. The control signal line L3 allows either a signal SEND going from the computer 1 side to the facsimile side or a signal SEND going in the opposite direction to pass therethrough, the line L4 allows either a signal INSTB going from the computer 1 side to the facsimile side or a signal INSTB going in the opposite direction to pass therethrough, and the line L5 allows either a signal TX/RX going from the computer 1 side to the facsimile side or a signal PE going from the facsimile side to the computer 1 side to pass therethrough. 
     More specifically, when the personal computer 1 outputs a high level H as the signal TX/RX, this signal is applied to the gate GA3 through a buffer BF2, thus causing G7, G9 and G12 out of the gate GA3 to close and G8, G10 and G11 to open. As a result, the signal SEND going from the computer 1 side to the facsimile 10 side, the signal INSTB going from the facsimile 10 side to the computer 1 side and the signal PE going from the facsimile 10 side to the computer 1 side, are disposed into such a state where they are able to pass through the gate GA3. At this time, a low level L is applied to a control terminal DIEN of the gate GA4 through an inverter IN1, thus setting 8-bit data going from the computer 1 side to the facsimile 10 side into such a state where it is able to pass through the gate GA4 (i.e., a transmission enable state as looked from the computer 1). 
     On the other hand, when the personal computer 1 outputs a low level L as the signal TX/RX, G7, G9 and G12 out of the gate GA3 are opened and G8, G10 and G11 are closed. As a result, the signal SEND going from the facsimile 10 side to the computer 1 side, the signal INSTB going from the computer 1 side to the facsimile 10 side and the signal TX/RX going from the computer 1 side to the facsimile 10 side are set into such a state where they are able to pass through the gate GA3. The gate GA4 is set into such a state where the signal going from the facsimile 10 side to the computer 1 side is able to pass therethrough (i.e., a reception enable state as looked from the computer 1 side). It is to be noted that, because the control signal line L5 is pulled up to a power source line through a resistor, it assumes a high level H in the above state unless the signal PE is applied thereto from the facsimile side. 
     Referring now to the computer interface circuit IFF equipped on the facsimile 10 side, as with the foregoing interface circuit IFP, a bidirectional gate GA1 with three state outputs is connected to the control signal lines L3, L4 and L5, and a bidirectional gate GA2 is connected to the 8 data lines. The gate GA1 also includes an exclusive OR gate EXOR having input terminals  ○1  and  ○2  to which are connected the control signal line L5 and a port P4 of an output port OP1, respectively, and having an output terminal which is connected to a control signal input terminal of the gate GA1 through a buffer BF1. As to the gate GA1, when an output level of the buffer BF1 assumes L, G1, G3 and G6 are closed but G2, G4 and G5 are opened, while when an output level of the BF1 assumes H, G1, G3 and G6 are opened but G2, G4, G5 are closed. The control signal line L1 and input terminals of the gates G1, G4 and G5 are connected to ports P1, P2, P3 and P4 of the output port OP1, respectively, and the control signal line L2 and output terminals of the gates G2, G3 and G6 are connected to ports P5, P6, P7 and P8 of an input port IP1, respectively. 
     An 8-bit data latch LA1 is connected to a data input terminal DI of the gate GA2. Data input terminals of the output port OP1, data output terminals of the input port IP1, a data output terminal D0 of the gate GA2 and data input terminals of the data latch LA1 are connected to 8-bit data buses D0-D7 which in turn are connected to the system control unit SCU. Address information of 16-bit output from the unit SCU is applied to a decoder DE1 so as to produce two chip select signals CS1 and CS2. The signal CS1 is applied to both the output port OP1 and the input port IP1, while the signal CS2 is applied to both the data latch LA1 and a NAND gate NA2. 
     Signals IOW and IOR are control signals which are produced from the control signals for a microprocessor in the system control unit SCU, and they assume a low level L when the I/O port is selected and a write strobe pulse or a read strobe pulse is issued, respectively. Accordingly, when the microprocessor in the SCU designates the port address, with which the signal CS2 is issued, and then writes predetermined data, the written data is latched by the data latch LA1 to be applied to the gate GA2 and, if a terminal DIEN of the gate GA2 is applied with a low level L, such 8-bit data is output to the connection cable CAB. Meanwhile, when the processor commands reading with that port address, the information on data lines of the connection cable is read into the data buses if the terminal DIEN of the gate GA2 assumes a high level H. 
     Furthermore, when the processor disignates the port address, with which the signal CS1 is issued, and then runs the writing operation, the lower 4-bit data on the data buses is issued from the output port OP1. And when it commands reading with that port address, the data is applied to the upper 4 bits of the data buses from the input port IP1. 
     FIGS. 4a and 4b show schematic operation of the system control unit SCU in the facsimile 10, FIG. 5 shows schematic operation of the personal computer 1, and FIGS. 6a and 6b show examples of signal timing for the interface circuit. 
     Operation of the system control unit SCU in the facsimile 10 will be first described by referring to FIGS. 4a and 4b. After the completion of initial setting, the unit SCU reads the state of a mode selection switch SW and then performs the operation in accordance with the set state thereof. The switch SW is, as shown in FIG. 2, connected to an operation board OPB. When the switch SW is turned to the manual side, the unit SCU is caused to control the system to operate in the same manner as the ordinary facsimile. 
     When the switch SW is turned to the automatic side, the signal ONLINE is first output. More specifically, the port address with which the chip select signal CS1 is issued is designated and then 8-bit data with its bit 0 being set at &#34;0&#34; (=L) is written. This causes the control signal line L1 of the interface cable CAB to be set at a low level L. 
     Next, the mode signal on the control signal line L2 is checked. This is done by reading data after designating the port address, with which the chip select signal CS1 is issued, and then by discriminating whether the bit 4 of 8-bit data appeared on the data buses is &#34;1&#34; or &#34;0&#34;. In this embodiment, it is supposed that the control signal of L (=&#34;0&#34;) offers a facsimile mode FAX and the same of H offers an input/output mode. Stated differently in summary, in this embodiment, a facsimile mode represents data transmission that is performed between the personal computer 1 and another facsimile connected through the telephone line, and an input/output mode represents data transmission that is performed between the facsimile 10 and the personal computer 1. 
     In case of an input/output mode, the level of the control signal line L5, i.e., the signal TX/RX, is checked. When the signal level assumes TX (low level L), the system control unit SCU is caused to set a mode where the image data read by the scanner ISA of the facsimile 10 is sent to the personal computer 1 side. 
     In this operation mode, the unit SCU of the facsimile 10 stores the image data obtained by the scanner ISA in the read/write buffer RWB one line by one line, and then outputs the data to the connection cable CAB through the interface circuit IFF. To inform the reception side (the personal computer 1 in this case) of that the data is now being issued, the signal SEND of low level is set on the control signal line L3 (to hold this state L) after issuing the 8-bit data. Then, the signal level of the control signal line L4 is monitored to wait for the signal INSTB of low level indicating the completion of reception and sent from the data reception side (computer 1) will appear on the line L4. When the signal INSTB appears thereon, the unit SCU clears the SEND signal and prepares subsequent data transmission. After the completion of reading and data transmission of the image data, the signal ONLINE on the control signal line L1 is cleared. 
     When the signal level of the control signal line L5 assumes RX (high level H), the unit SCU is caused to set a mode where the data sent out of the personal computer 1 is recorded by the plotter REC. In this mode, the unit SCU first sets the plotter to start and then begins data reception after checking both the end of data and the residual quantity of recording paper sheets. In data reception, the level of the control signal line L3 is monitored and 8-bit data on the data lines is then read as the SEND signal has arrived. The read data is stored in the read/write buffer RWB and, when the data of one line has been completely stored, the unit SCU provides an output to the plotter REC. 
     The unit SCU outputs the signal INSTB to the control signal line L4 for confirmation for each data reception. When the residual quantity of recording paper sheets is reduced, the signal PE of low level is output on the control signal line L5 to inform the reception side (the computer 1) of the fact. When the end of data is detected, the signal ONLINE on the control signal line L1 is cleared. Incidentially, the unit SCU detects the end of data in this embodiment by clocking the lapsed time from the previous data reception, and if the lapsed time reaches a predetermined value, this is judged as the end of data. 
     There will now be described a facsimile mode (see FIG. 4b). Also in this mode, the unit SCU first checks the level of the control signal line L5, i.e., the control signal TX/RX. In this embodiment, when that signal level assumes TX (low level), the unit SCU sets a mode (reception/transfer mode) where the information transmitted from another facsimile connected through the telephone line is transferred to the personal computer 1. And when that signal level assumes RX (high level), the unit SCU sets a mode (transmission/transfer mode) where the data sent out of the personal computer 1 is transmitted to another facsimile connected through the telephone line. 
     In case of RX (a transmission/transfer mode), the unit SCU first clears the signal ONLINE on the control signal line L1 and then starts preparation for facsimile transmission. This process is proceeded similarly to the ordinary facsimile transmission as follows. 
     (a) Calling: the counterpart facsimile is called by dialing the telephone set. 
     (b) Confirmation of calling party: a tone of 2100 Hz is sent out to inform that the calling party is a facsimile terminal. 
     (c) Confirmation of function: the function of the calling party is informed using the low speed modem (FSK) of 300 bps. 
     (d) Command information: transmission parameters (transmission rate of the high speed modem, etc.) is informed using the low speed modem. 
     (e) Training: matching of the high speed modem with the line is made and a predetermined data pattern is sent to check a data transmission error rate. 
     (f) Response after training: when the data transmission error rate after training is less than a certain value, &#34;Completion of Reception Preparation&#34; is informed to proceed to the next step. When the rate is larger than a certain value, &#34;Request of Retraining&#34; is repeated. 
     After the completion of transmission preparation, the signal ONLINE is set on the control signal line L1 and then the end of data as well as arrival of the SEND signal are both checked. Upon arrival of the SEND signal, the unit SCU receives 8-bit data on the data lines from the computer interface IFF and stores the same in the read/write buffer RWB. Subsequent to such data input, the signal INSTB is issued onto the control signal line L4. When the data of one line is completely stored, data compression processing is started and, after this processing, data transmission (to another facsimile) is started. It is to be noted that, in this embodiment, data compression processing and data transmission processing are run under interrrupt processing so as to avoid a shift in timing. Incidentially, during transmission of data the control signal ONLINE for the computer interface IFF is cleared to inhibit the computer side from entering the data transmission operation. 
     After the end of data was detected and transmission of all the data stored in the memory was completed, the unit SCU commands processing for ending the facsimile transmission, clears the signal ONLINE and then returns to checking of the switch SW. 
     In an operation mode (reception/transfer mode) where the control signal line L5 assumes a low level TX, it waits for a reception request from the facsimile (counterpart) on the transmission side. Upon a reception request, connection processing on the reception side is performed similarly to the above mentioned preparation for facsimile transmission, and data reception is then started. Compressed data reproduction processing is implemented for each reception of 1-line data and, after the completion of this processing, the individual 8-bit data are output to the computer interface IFF. At the same time, the unit SCU sets the signal SEND on the control signal line L3 and then waits for that the signal INSTB to appear on the control signal line L4. Upon arrival of the signal INSTB, the signal SEND is cleared and thereafter the above process is repeated until all of the 1-line data will be transmitted. After reception from the counterpart facsimile is terminated and the data stored in the memory of the facsimile 10 is all transmitted to the personal computer 1 completely, the unit SCU commands processing for ending the facsimile transmission, clears the signal ONLINE and then returns to checking of the switch SW. 
     Next, schematic operation of the personal computer 1 will be described by referring to FIG. 5. After the completion of initial setting processing, the CPU of the computer 1 checks the level of the control signal line L1. If, the level is set at ONLINE, it proceeds to designation of an operation mode. In other words, thereafter it runs the operation set in accordance with key-in operation effected on the personal computer 1 by an operator. 
     In this embodiment there are four operation modes; a mode where the data in the computer 1 is recorded by the plotter REC (recording mode), a mode where the data read by the scanner ISA is input to the computer 1 (image input mode), a mode where the data in the computer 1 is transmitted to another facsimile (transmission/transfer mode), and a mode where the data received from another facsimile is input to the computer 1 (reception/transfer mode). As to processing effected on the computer 1 side, however, there are primary two types of operation modes (image output mode and image input mode), because the input/output mode (recording mode, image input mode) and the facsimile mode (transmission/transfer mode, reception/transfer mode) are different from each other just in their signal levels issued to the control signal line L2. 
     In a mode (image output mode) where data is sent from the computer 1 side to the plotter REC or another facsimile, the CPU of the computer 1 first sets the level of the control signal line L5 at RX and then starts data sending. During this processing, the signal ONLINE on the control signal line L1 and the signal PE on the control signal line L5 are both checked. Subsequent to output of 8-bit data, the CPU sets the SEND signal on the control signal line L3 and, upon arrival of the signal INSTB through the control signal line L4, it clears the SEND signal and then prepares for the next data transmission. After all the data has been transmitted completely, it returns to checking of the signal ONLINE. 
     In a mode (image input mode) where data is input to the computer 1 from another facsimile or the scanner ISA, the CPU of the computer 1 first sets the control signal line L5 at TX (low level) and then checks the signal ONLINE on the control signal line L1. With this signal being issued, it waits for arrival of the SEND signal through the control signal line L3. Upon arrival of the SEND signal, the CPU receives 8-bit data on the data lines and stores the data in the memory at the predetermined address, and then it issues the signal INSTB  indicating the completion of reception onto the control signal line L4 and waits for arrival of the next data. If the signal ONLINE disappears, the CPU proceeds to designation of an operation mode after waiting for that the signal ONLINE will appear once again, and thereafter these processes will be repeated. 
     Accordingly, in case data is transmitted, for example, from the computer 1 side to the facsimile 10 side, the signals as shown in FIG. 6a appear on the interface cable CAB. More specifically, when the facsimile 10 outputs the ONLINE signal, the computer 1 outputs the predetermined 8-bit data onto the data lines and subsequently otuputs the SEND signal onto the control signal line L3. After confirming the SEND signal, the facsimile 10 takes in the 8-bit data on the data lines and outputs the INSTB signal to inform reception on its side. After confirming the INSTB signal, the computer 1 clears the SEND signal and then prepares for the next data transmission. 
     By referring to FIG. 6b there will be now be described in detail operation of the facsimile 10 and the computer 1 in case the residual quantity of recording paper sheets becomes small during reception of data from the computer 1 by the facsimile 10, i.e., during recording by the plotter REC. In this mode, the signal TXRX issued from the computer 1 assumes a high level H at the beginning, so that G11 is opened and G12 is closed. The control signal line L5 indicates a high level H because it is pulled up to the power source line through a resistor. This causes the terminal ○1  of the exclusive OR gate EXOR on the facsimile side to assume H and normally the terminal  ○2  also assumes H, so that its output terminal becomes L to make G5 of the gate GA1 open and G6 thereof closed. The facsimile 10 normally sets the port P4 of the output port OP1 at a high level H, but it outputs a low level L at the port P4 when recording paper sheets are decreased in the residual quantity. This signal is output onto the control signal line L5 through the gate G5 to become the signal PE indicating the decreased residual quantity of recording paper sheets. Since the gate G11 is opened on the computer 1 side, this signal PE is sent to the computer 1. Upon arrival of this signal, after sending the predetermined data the computer 1 stops transmission of data and then sets the control signal line L5 at a TX level. When the control signal line L5 becomes a TX level (L), the output level of the gate EXOR on the facsimile side is inverted to H causing G5 of the gate GA1 to close and G6 thereof to open, so that the TX level is applied to the port P8 of the input port IP1. By monitoring the level at the port P8, the facsimile 10 recognizes the fact that the RX mode (transmission/transfer mode) has changed into the TX mode (reception/transfer mode). 
     Although switching between a facsimile mode and an input/output mode was made using the control signal line in the foregoing embodiment, this mode setting may be performed by sending the given control code through the 8-bit data lines. Further, although a specific control signal line was prepared for sending the signal ONLINE indicating whether or not the facsimile 10 is in such a state as enabling communication with the computer 1 in the foregoing embodiment, it is also possible to pass both the signal ONLINE and the signal PE indicating the decreased residual quantity of recording paper sheets through the same single line. By so doing, the control signal lines L1 and L2 in the illustrated embodiment becomes needless, thus resulting in the less number of signal lines. Moreover, although the confirmation signal INSTB was used in the foregoing embodiment to improve reliability of signal transmission, that signal may be dispensed with. In such case, confirmation of the signal INSTB is omitted and the SEND signal is so controlled as to be output for a predetermined time on the transmission side. Consequently, what is required at minimum is only bidirectional data lines of 8 bits and two bidirectional control signal lines L3, L5. 
     In addition, although the foregoing embodiment used the normal image data for data transmission between the facsimile 10 and the computer 1, the compressed and coded data may be transmitted as an alternative. In such case, since the amount of data is decreased, the time necessry for data transmission is shortened. Finally, although a personal computer was connected to a facsimile apparatus in the foregoing embodiment, other equipments which have an equivalent function, such as word processors, office computers or intelligent terminal units, are also connectable to the facsimile apparatus. 
     According to the embodiment as described above, data transmission is enabled between a facsimile apparatus and a computer or so, and an interface circuit is simplified in its configuration. In particular, a part of both data lines and control signal lines is formed of bidirectional lines and this permits high-speed data transmission using less signal lines. 
     Other various modifications will become possible for those skilled in the art after receiving the teachings of the present disclosure without departing from the scope thereof.