Patent Publication Number: US-7724035-B2

Title: Data transmission system and cable

Description:
This is a divisional of application Ser. No. 11/137,478 filed May 26, 2005 now U.S. Pat. No. 7,446,571. The entire disclosure(s) of the prior application(s), application Ser. No. 11/137,478 is considered part of the disclosure of the accompanying divisional application and is hereby incorporated by reference. 

   FIELD OF THE INVENTION 
   The invention relates to a wired digital data transmission system, particularly to a data transmission system for transmitting and receiving binary signals between multiple electronic equipment each provided with an individual power supply and a cable used therein. 
   BACKGROUND OF THE INVENTION 
   A conventional data transmission system as illustrated by a circuit diagram in  FIG. 4(A)  comprises multiple electronic equipment  10 ,  20  each provided with an individual power supply, and a cable  30  for connecting therebetween. The data transmission system includes two sets of data transmitting circuits each having an open drain type output section at a transmitting end and an input section provided with a pull-up type resistor at a receiving end, and these data transmitting circuits extend between the electronic equipment  10 ,  20  and the cable  30 . A first digital data transmitting circuit is provided for transmitting data from the electronic equipment  10  to the electronic equipment  20  while a second digital data transmitting circuit is provided for transmitting data from the electronic equipment  20  to the electronic equipment  10  in an opposite direction. 
   The electronic equipment  10  (first electronic equipment) comprises a power supply  11  of an output voltage Va, an internal circuit  14  for effecting various data processing adaptable to intend applications, a transmitting circuit  12  for subjecting transmission data supplied from the internal circuit  14  to a proper coding processing or modulating processing such as a parallel-serial conversion and the like so as to adjust a data format, an open drain type output section  13  (first output section) for binarizing an output signal from the transmitting circuit  12  and transmitting the binarized output signal to the electronic equipment  20  by way of the cable  30 , an input section  16  (second input section) for waveform shaping a binary signal supplied from the electronic equipment  20  by way of the cable  30  and inputting thereto, a pull-up resistor Ra (second resistor) which is attached to the input side of the input section  16 , and a receiving circuit  15  for subjecting the received data inputted to the input section  16  to a proper decoding processing or demodulating processing such as serial-parallel conversion and the like so as to adjust a data format and supplying it to the internal circuit  14 . 
   The transmitting circuit  12 , the internal circuit  14 , the receiving circuit  15 , the input section  16  are respectively operated under the output voltage Va while the pull-up resistor Ra is connected to a power supply line of the output voltage Va at one end and also connected to an input line of the input section  16  at the other end so as to perform its function utilizing the output voltage Va. On the other hand, the open drain type output section  13  is employed so as to supply a signal without dependence on the output voltage Va of its own electronic equipment  10 . That is, the output section  13  is rendered in a ground state in its output when an output value thereof is low while it is rendered in a high impedance state (floating state, high resistive state) in its output when the output value is high. 
   The electronic equipment  20  (second electronic equipment) that is a communication counterpart of the electronic equipment  10  comprises a power supply  21  of an output voltage Vb, an internal circuit  24  for effecting various data processing adaptable to intend applications, a transmitting circuit  25  for subjecting transmission data supplied from the internal circuit  24  to a proper coding processing or modulating processing such as a parallel-serial conversion and the like so as to adjust a data format, an open drain type output section  26  (second output section) for binarizing an output signal from the transmitting circuit  25  and transmitting the binarized output signal to the electronic equipment  10  by way of the cable  30 , an input section  23  (first input section) for waveform shaping a binary signal supplied from the electronic equipment  10  by way of the cable  30  and inputting thereto, a pull-up resistor Rb (first resistor) which is attached to the input side of the input section  23 , and a receiving circuit  22  for subjecting the received data inputted to the input section  23  to a proper decoding processing or demodulating processing such as serial-parallel conversion and the like so as to adjust a data format and supplying it to the internal circuit  24 . 
   The input section  23 , the receiving circuit  22 , the internal circuit  14  and the transmitting circuit  25  are respectively operated under the output voltage Vb while the pull-up resistor Rb is connected to a power supply line of the output voltage Vb at one end and also connected to an input line of the input section  23  at the other end so as to perform its function utilizing the output voltage Vb. On the other hand, an open drain type output section  26  is employed so as to supply a signal without dependence on the output voltage Vb of its own electronic equipment  20 . That is, the output section  26  is rendered in ground state in its output when an output value thereof is low while it is rendered in a high impedance state (floating state, high resistive state) in its output when the output value is high. 
   The cable  30  has a connector  31  provided at its one end at the electronic equipment  10  side and another connector  32  provided at its other end at the electronic equipment  20  side, and also it has a long intermediate portion which is flexible and soft so that a physical connection between the electronic equipment  10  and electronic equipment  20  can be dynamically and simply established in compliance with the necessity of communication. Multiple signal transmission lines  33 ,  35  and a ground line  34  which are respectively made of copper wire and the like, and insulatively coated, and built in the cable  30 . The lines  33 ,  34 ,  35  are respectively connected to corresponding contact terminals of the connector  31  at each one end and also connected to corresponding contact terminals of the connector  32  at each other end. The ground line  34  may be connected to a shield or may act as a shield. 
   When the electronic equipment  10  and the electronic equipment  20  are connected to each other by the cable  30 , the output line of the output section  13 , the signal transmission line  33  and the input line of the input section  23  are connected to one another, and the ground line of the electronic equipment  10 , the line  34  and the ground line of the electronic equipment  20  are connected to one another while the output line of the output section  26 , the line  35  and the input line of the input section  16  are connected to one another. That is, a first digital data transmitting circuit for transmitting a binary signal from the electronic equipment  10  to the electronic equipment  20  is formed of the output section  13 , the line  33  and the input section  23 , while a second digital data transmitting circuit for transmitting a binary signal from the electronic equipment  20  to the electronic equipment  10  in an opposite direction is formed of the output section  26 , the line  35  and the input section  16 . 
   The connector  31  is mounted onto the electronic equipment  10  and the connector  32  is mounted onto the electronic equipment  20 , and the electronic equipment  10  and the electronic equipment  20  are connected to each other by the cable  30  so as to transmit data in order to transmit and receive data between the electronic equipment  10 ,  20 . In this state, the transmission of data from the electronic equipment  10  to the electronic equipment  20  is effected by the first digital data transmitting circuit (output section  13 →line  33 →input section  23 ), while the transmission of data from the electronic equipment  20  to the electronic equipment  10  is effected by the second digital data transmitting circuit (output section  26 →line  35 →input section  16 ). 
   More in detail, an output state of the output section  13  (or  26 ) is changed between a ground state and a high impedance state as data value to be transmitted is low or high or ever changed so that the line  33  (or  35 ) is rendered in the ground state when a low data value is outputted. Such a ground state is inputted to the input section  23  (or  16 ) so that the low data value is transmitted. On the other hand, when a high data value is outputted, the signal transmission line  33  (or  35 ) is separated from the ground and is rendered in an output voltage Vb (or Va) application state by way of the pull-up resistor Rb (or Ra) and such a state is inputted to the input section  23  (or  16 ) so that the high data value is transmitted. 
   According to the conventional data transmission system, since the open drain type output sections  13 ,  26  are employed at the transmitting end while the input sections  23 ,  16  provided with the pull-up resistor Rb, Ra are employed at the receiving end, even if the electronic equipment  10 ,  20  are provided with individual power supplies  11 ,  21  and operate by their own power supply voltages Va, Vb, they can be connected to each other so as to transmit data by the cable  30  without being bound by the output voltage Va, Vb of the communication counterpart. 
   Although line capacitance is intensively illustrated on the lines  33 ,  35  of the cable  30 , a capacitance C which distributes between the ground line  34  and a shield or other coating line or the like is parasitic on the lines  33 ,  35 . The capacitance C has a property to increase substantially in proportion to the lengths of the lines  33 ,  35 , and it is generally considerably larger than the capacitance which is parasitic on each circuit inside equipment. When the signals on the lines  33 ,  35  are changed from a low state to a high state, they slow down by time constant (resistance Rb×capacitance C), (resistance Ra×capacitance C), in accordance with the combination of the capacitance C, resistors Rb, Ra at rising of the signals. 
   Accordingly, if the data transmission rate is suitable, it is possible to obtain a signal waveform which clearly shows a binary state (see waveform example at the time of low transmission rate shown in  FIG. 4B ). If the data transmission rate is increased from the foregoing rate, the signal waveform is collapsed, particularly a high state is not made clear (see the waveform example at the time of high transmission rate shown in  FIG. 4C ) so that the data is not transmitted accurately, causing a problem that it is difficult to speed up data transmission or increase data transmission rate. 
   Although various standards and the like capable transmitting data at high speed are proposed and in practical use, the restriction imposed on a cable and a transmitting circuit become severe as the data transmission is speeded up, a driving voltage and other bindings are imposed on a driving condition of the signal transmission line. 
   Under the circumstances, at present if data is transmitted without being bound by a counterpart&#39;s power supply voltage, a transmission rate is restricted, while if data is transmitted by increasing the transmission rate, the data transmission is bound by the counterpart&#39;s power supply voltage. 
   It becomes a technical problem to increase the transmission rate while following an open drain type transmission system adaptable for a different power supply so as to meet both advantages, namely, not to be restricted in transmission rate and not to be bound by the counterpart&#39;s power supply voltage. 
   SUMMARY OF THE INVENTION 
   The invention has been made to solve the problem of the conventional data transmission system, and it is an object of the invention to realize a data transmission system capable of transmitting data at high speed without being bound by a counterpart&#39;s power supply voltage. 
   It is another object of the invention to realize a cable for data transmission which is suitable for the data transmission system. 
   Configurations, operations, and effects of first and second solving means invented for solving the problem of the conventional data transmission system are described hereinafter. 
   First Solving Means: 
   The data transmission system of the first solving means comprises, multiple electronic equipment having individual power supplies, a cable for connecting the electronic equipment so as to transmit signals therebetween, and digital data transmitting circuits extending between the electronic equipment and the cable and having open drain type output sections at transmitting side and input sections provided with pull-up type resistors at receiving ends, wherein either or both of the resistors and output sections are moved to the cable. 
   Further, the cable for data transmission which is suitable for the data transmission system incorporates therein, a first signal transmission line having both ends extending to both ends of the cable, a push-pull type first driving circuit which is put in the first signal transmission line and connected thereto, a power supply line which is extending from a power terminal of the first driving circuit to the end of the cable at the output side of the first driving circuit, and a pull-up type first resistor which is connected to the power supply line at one end and also connected to the input side of the first driving circuit of the first signal transmission line at the other end. 
   Alternatively, the cable further comprises, a second signal transmission line having both ends extending to both ends of the cable, and an open drain type second driving circuit which is put in and connected to the second signal transmission line, namely, a moved second output section. 
   According to the data transmission system of the first solving means, the pull-up type resistor or the open drain type output section is moved to the cable so that the distance therebetween is shortened in length, thereby shortening the length of the part, which is charged and the like by way of the pull-up type resistor, of the signal transmission line inside the cable. 
   As a result, since parasitic capacitance of the part which is charged and the like becomes small, time constant which restricted the rising of a signal becomes small if the resistance value is the same. Accordingly, the change of a signal waveform on the transmission line is made abruptly in a short time, so that the signal waveform is hardly collapsed even if the data transmission rate is increased, thereby maintaining clear state. 
   Accordingly, the invention can realize the data transmission system capable of transmitting data at high speed without being bound by the counterpart&#39;s power supply voltage. 
   Second Solving Means: 
   The data transmission system of the second solving means comprises, first and second electronic equipment having individual power supplies, a cable for connecting between the first and second electronic equipment so as to transmit signals therebetween and having a connector at one end of at least the first electronic equipment side irrespective of the presence of connector at one end of the second electronic equipment side, a first digital data transmitting circuit extending between the first electronic equipment, the cable and the second electronic equipment and having an open drain type first output section at the first electronic equipment side, and a first input section provided with a pull-up type first resistor at the second electronic equipment side, and a second digital data transmitting circuit extending between the first electronic equipment, the cable and the second electronic equipment, and having an open drain type second output section at the second electronic equipment side, and a second input section provided with a pull-up type second resistor at the first electronic equipment side, wherein the first resistor and the second output section are moved from the second electronic equipment to the connector. 
   Further, the cable for data transmission which is suitable for the data transmission system incorporates therein, a first signal transmission line and a second signal transmission line having a connector provided at least one end of the cable, and both ends thereof extending to both ends of the cable, the cable further comprises a push-pull type first driving circuit which is put in the first signal transmission line within the connector and connected to a line, part of the first signal transmission line extending to the end of the cable at the connector side at its input side (i.e., input terminal or input line of the first driving circuit) and also connected to a line, part of the first signal transmission line opposite to the line, part of the first signal transmission line at its output side (i.e., output terminal or output line of the first driving circuit), a power supply line extending from a power terminal of the first driving circuit to the output side of the first driving circuit, i.e., to the end of the cable opposite thereto, a pull-up type first resistor connected to the power supply line at one end, and also connected to an input side of the first driving circuit of the first signal transmission line at the other end, an open drain type second driving circuit which is put in the second signal transmission line, and connected to a line, part of the second signal transmission line extending to the end of cable at the connector side of the second signal transmission line at its output side (i.e., output terminal or output line of the second driving circuit), and also connected to a line, part of the second signal transmission line opposite to the line, part of the second signal transmission line at its input side (i.e., input terminal or input line of the second driving circuit). 
   According to the cable for the data transmission system of the second solving means, data is transmitted from the first electronic equipment to the second electronic equipment by the first digital data transmitting circuit by way of the cable while data transmitted from the second electronic equipment to the first electronic equipment by the second digital data transmitting circuit by way of the cable so that two-way communication is effected. Further, according to both the first and second digital data transmitting circuit, a combination of the open drain type output section and the pull-up type resistor is kept therein but the installing positions thereof are moved to the cable so as to render parasitic capacitance small. Further, the part where the open drain type output section and the pull-up type resistor are moved to the connector in the cable which is the closest to the first electronic equipment so that the parasitic capacitance becomes the smallest irrespective of the length of the cable. Still further, the first resistor and the second output section are moved to the cable, which relates to the second electronic equipment and the connector but not relates to the first electronic equipment. 
   As a result, the data transmission system of the invention can be simply built in the first electronic equipment which has been conventionally used by attaching the connector to or detaching the connector from the cable, and further the operation and the effect of the invention are immediately achieved by merely increasing the operation speed of the transmitting and receiving sections. This effect is achieved more effectively. 
   Accordingly, the invention can realize the data transmission system capable of transmitting data at much higher speed without being bound by the counterpart&#39;s power supply voltage which is familiar with existing electronic equipment. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1(A)  to (C) show a data transmission system according to a first embodiment of the invention wherein  FIG. 1(A)  is a circuit diagram,  FIG. 1(B)  shows an example of a waveform at low transmission rate, and  FIG. 1(C)  shows an example of a waveform at high transmission rate; 
       FIGS. 2(A) ,  2 (B),  2 (C) show a data transmission system in detail according to a second embodiment of the invention, respectively showing an open drain type circuit; 
       FIGS. 3(A) ,  3 (B),  3 (C) show a data transmission system in detail according to a third embodiment of the invention, respectively showing a push-pull type circuit; and 
       FIG. 4(A)  to (C) show a conventional data transmission system wherein  FIG. 4(A)  is a circuit diagram,  FIG. 4(B)  shows an example of a waveform at low transmission rate, and  FIG. 4(C)  shows an example of a waveform at high transmission rate. 
   

   PREFERRED EMBODIMENT OF THE INVENTION 
   First Embodiment 
   A concrete configuration of the data transmission system according to the first embodiment of the invention is described with reference to  FIGS. 1(A) to 1(C) , which are compared with  FIGS. 4(A) to 4(C)  of the conventional data transmission system, in which  FIG. 1(A)  is a circuit diagram. The data transmission system shown in  FIG. 1(A)  is different from that shown in  FIG. 4(A)  in respect of an electronic equipment  40  (second electronic equipment) formed by partially improving the electronic equipment  20  shown in  FIG. 4(A) , and a cable  50  formed by partially improving the cable  30  shown in  FIG. 4(A) . The electronic equipment  10  shown in  FIG. 1(A)  is the same as that shown in  FIG. 4(A) . 
   More in detail, the pull-up type resistor Rb (first resistor) provided in the electronic equipment  20  of the conventional data transmission system and the open drain type output section  26  (second output section, second driving circuit) provided in the same electronic equipment  20  are respectively moved to a connector  51  of the cable  50 . 
   The cable  50  has the connector  51  instead of the connector  31  in  FIG. 4(A)  at the electronic equipment  10  side, of which a push-pull type buffer  53  (first driving circuit) is put in a line  33  (first signal transmission line). An input terminal of the buffer  53  is connected to a short line of the line  33 , a part of the line  33  extending to the end of the connector  51  (i.e., a part for receiving an output of an output section  13 ) while an output terminal of the buffer  53  is connected to a long line of the line  33 , a part of the line  33  opposite to the short line (i.e., a part extending to the connector  32  by way of an intermediate part of the cable  50  of the line  33 ). A ground terminal of the buffer  53  is connected to a line  34  within the connector  51 , and a power supply terminal (power supply and reception section) of the buffer  53  is connected to a vacant line contained in the cable  50  or a line  52  (power supply line) which is assigned thereto by newly adding. 
   The line  52  extends in parallel with the line  33  in the cable  50  and reaches the connector  32  (end of the cable at the output side), and it is connected to a vacant terminal of the connector  32  or to a contact terminal added to the connector  32 . 
   The pull-up type resistor Rb is connected to the line  52  at one end within the connector  51  and is connected to a short part corresponding to the input side of the buffer  53  of the line  33  at the other end. 
   Although the output section  26  is put in a line  35  (second signal transmission line) within the connector  51 , it is connected to the buffer  53  in an opposite direction. That is, an output terminal of the output section  26  is connected to a short line of the line  35 , a part of the line  35  extending to the end of the connector  51  side of the line  35  (i.e., a part extending to an input section  16 ) while an input terminal of the output section  26  is connected to a long line of the line  35 , a part of the line  35  at the opposite side (i.e., a part extending to the connector  32  of the line  35  by way of the intermediate part of the cable  50 ). Although a ground terminal of the output section  26  is connected to the line  34  within the connector  51 , the output section  26  is not connected to a power supply line and the like because it is an open drain type which does not require the supply and reception of a power supply. 
   The electronic equipment  40  is configured such that the pull-up type resistor Rb is moved to the connector  51  of the cable  50  and displaced from the electronic equipment  40  regarding the first digital data transmitting circuit (output section  13 →line  33 →input section  23 ), and the line which is divided from the power supply line of a voltage Vb is wired to reach an a counterpart&#39;s connector of the connector  32  corresponding to the line  52  extending from the pull-up type resistor Rb within the cable  50  to reach the connector  32 , wherein when the connector  32  is installed on the electronic equipment  40 , the line  52  and the power supply line of the voltage Vb are rendered conductive. 
   The electronic equipment  40  in the second digital transmitting circuit (output section  26 →line  35 →input section  16 ) has a push-pull type buffer  41  (alternative driving circuit) provided on a part where the output section  26  was provided before it was moved to the connector  51  (i.e., position corresponding to the output section  26  of the electronic equipment  20  before it was improved) corresponding to a case where the open drain type output section  26  is moved to the connector  51  of the cable  50  and displaced from the electronic equipment  40 . The buffer  41  receives an output of a transmitting circuit  25  in the same manner as the previous output section  26 , and outputs an output to the line  35  by way of the connector  32  which however operates under a power supply voltage Vb, which is different from the output section  26 . That is, the pull-up type buffer  41  renders an output in a ground state in the same manner as the push-pull type buffer  53  when the output value is low while it renders the output in a power supply voltage state when the output value is high wherein electric current flows with low resistance in any state. If the transmitting circuit  25  is formed of a push-pull type and has a sufficient power, the pull-up type buffer  41  may be not provided so as to short circuit the signal line. 
   A manner of use and operation of the data transmission system of the first embodiment is described more in detail with reference to  FIGS. 1(B) and 1(C)  wherein  FIG. 1(B)  shows an example of a waveform at low transmission rate, and  FIG. 1  (C) shows an example of a waveform at high transmission rate which are respectively compared with  FIGS. 4(B) and 4(C) . 
   Although portable equipment such as a portable telephone is exemplified as a typical example of the electronic equipment  10 , a fixedly used electronic equipment may be used. Although a personal computer, a portable information terminal, a mail terminal, a browser board and the like are exemplified an a typical example of the electronic equipment  20 , they are not limited to such an electronic equipment. Although a two-way serial communication in which a UART (Universal Asynchronous Receiver Transmitter) is built and which is capable of shifting and changing a band rate is exemplified as a typical example of the data transmission system, the data transmission system is not always such two-way serial communication. 
   In any case, when the electronic equipment  10  and electronic equipment  40  are connected to each other by the cable  50 , more in detail, when the connector  51  is mounted onto the electronic equipment  10  while the connector  32  is mounted on the electronic equipment  40 , the output line of the output section  13 , a short part of the divided line  33 , the buffer  53 , a long part of the divided line  33  and the input line of the input section  23  are connected to one another so as to establish the first digital data transmitting circuit, which is rendered in a state where the binary signal can be transmitted from the electronic equipment  10  to the electronic equipment  40 . At the same time, the output line of the buffer  41 , a long part of the divided line  35 , the output section  26 , a short part of the divided line  35  and the input line of the input section  16  are connected to one another so as to establish the second digital data transmitting circuit, which is rendered in a state where the binary signal can be transmitted from the electronic equipment  40  to the electronic equipment  10 . 
   When data is transmitted and received between the electronic equipment  10  and electronic equipment  40  which are connected to each other so as to transmit data, the output state of the output section  13  is changed between a ground state and a high impedance state in the first digital data transmitting circuit (output section  13 →line  33 →buffer  53 →line  33 →input section  23 ) as the data value to be transmitted is low or high, or ever changed, so that the short line  33  is rendered in a ground state when low data value is outputted, and the same ground state is inputted to the buffer  53  so that the long line  33  to which the data value is outputted is also rendered in the ground state and also the same state is inputted to the input section  23  so as to transmit the low data value. On the other hand, when high data value is outputted, the short line  33  is separated from the ground and rendered in the voltage Vb application state by way of the pull-up type resistor Rb, while when the same state is inputted to the buffer  53 , the long line  33  to which the data value is outputted is rendered conductive to the line  52  with low resistance by way of the buffer  53 , and such an active driving establishes the voltage Vb application state, and further the same state is inputted to the input section  23  so as to transmit high data value. 
   The output state of the buffer  41  is changed between a ground state and a voltage Vb application state in the second digital data transmitting circuit (buffer  41 →line  35 →output section  26 →line  35 →input section  16 ) as the data value to be transmitted is low or high, or ever changed, so that the long line  35  is rendered in a ground state when low data value is outputted, and the same ground state is inputted to the output section  26  so that the short line  35  to which data value is outputted is also rendered in the ground state and also the same state is inputted to the input section  16  so that the low data value is transmitted to the input section  16 . On the other hand, when the high data value is outputted, the long line  35  is rendered in the voltage Vb application state, and this state is inputted to the output section  26  so that the short line  35  to which data value is outputted is separated from the ground and is rendered in the voltage Va application state by way of the pull-up type resistor Ra, and the same state is inputted to the input section  16  so that high data value is outputted. 
   Although the buffer  53  or the buffer  41  is put or added also in this case, the transmission is effected by the open drain type output sections  13 ,  26  and the reception is effected by the input sections  23 ,  16  to which pull-up type resistors Rb, Ra are directly or indirectly attached. Accordingly, even if the electronic equipment  10 ,  40  is provided with individual power supplies  11 ,  21  so that they can be operable by their own power supply voltages Va, Vb, there keeps an advantage that they can be connected by the cable  50  so as to transmit data therebetween without being bound by the communication counterpart&#39;s power supply voltages Va, Vb. 
   Further, the line  33  and the line  35  of the cable  50  are divided by the buffer  53  and output section  26  within the connector  51  while both the lines  33 ,  35  are driven by the combination of the open drain type output sections  13 ,  26  and pull-up type resistors Rb, Ra at each short part, and driven by the push-pull type buffers  53 ,  41  at each long part. The distributed capacitance C is parasitic (although only the line capacitance is intensively illustrated) between each long line which occupies most parts of the lines  33 ,  35  and the line  34 , shield, other coated material and the like in the same manner as the conventional data transmission system. On the other hand, a small capacitance Cs is parasitic (although only the line capacitance is intensively illustrated) between each short line of the lines  33 ,  35  located adjacent to the electronic equipment  10  side and the line  34 , shield, other coated material and the like. The capacitance Cs at the short part is much smaller than the capacitance C at the long part without dependency on the length of the cable  50 . 
   When signals on the lines  33 ,  34 , and  35  are changed from a low state to a high state, the waveforms of the signals when rising are determined by the combination of the small capacitance Cs and the resistors Rb, Ra but not determined by the large capacitance C. More in detail, the waveforms of the signals are restricted by a time constants (Rb×Cs), (Ra×Cs). 
   Accordingly, it is needless to say that the waveforms of the signals in a clear binary state (high and low data values are clear) can be obtained within the same data transmission rate as made conventionally (see examples of waveforms at the low transmission rate as shown in FIG.  1 (B)), and even if the data transmission rate is increased, waveforms of the signals are hardly collapsed and the waveforms of the signals in a clear binary state can be obtained, so that the data can be transmitted accurately even if it is speeded up (see examples of waveforms at the high transmission rate as shown in  FIG. 1(C) ). 
   Accordingly, data can be transmitted at higher transmission rate than the conventional rate. It is not generally told because transmission rate is changed depending on the length of the cable and the like, but the upper limit of the data transmission rate is improved to an extent of about several MHz whereupon the upper limit data transmission rate has been conventionally about several hundred kHz. If the electronic equipment  10  is configured such that the data transmission rate can be changed by operating a menu or data transmission rate can be automatically changed during the communication while the communication is effected at a given low transmission rate at first, the invention can be directly applied to the conventional existent electronic equipment  10 . 
   Second Embodiment 
     FIGS. 2(A) , (B), (C) show open drain type output sections/driving circuits in detail.  FIG. 2(A)  shows an open drain type output section/driving circuit using a MOS transistor, and  FIG. 2(B)  shows the output section/driving circuit using an NPN transistor, and also  FIG. 2(C)  shows the output section/driving circuit using a switch. Even if the output section/driving circuit uses other devices, they correspond to an open drain type output section/driving circuit provided that an output state of an element or circuit is changed between a short circuit state/low resistance conductive state relative to a reference potential such as a ground and the like and a high impedance state. 
   Third Embodiment 
     FIGS. 3(A) , (B), (C) show push-pull type driving circuits in detail.  FIG. 3(A)  shows a driving circuit using a C-MOS transistor, and  FIG. 3(B)  shows a driving circuit using a totem pole bipolar transistor pairs, and also  FIG. 3(C)  shows a driving circuit using an voltage follow type transistor. Even if the driving circuit uses other devices, they correspond to a push-pull type driving circuit provided that the output state of an element or circuit is changed between a short circuit state/low resistance conductive state relative to a reference potential such as a ground and the like and a short circuit state/low resistance conductive state relative to a reference potential such as a power supply voltage and the like. 
   Other Embodiments 
   The pull-up type resistors Ra, Rb are not limited to be formed of a single resistor element and they may be formed of a combination of multiple elements or formed of a resistor network. 
   Although not shown in drawings, an input protective register, a protective diode, level conversion means, hysteresis property may be added to the input sections  16 ,  23 . 
   The power supplies  11 ,  21  may be formed of cells or not formed of cells. If the power supplies  11 ,  21  are individually provided, the power supply voltages Va, Vb may be the same or not the same, either of which may be higher than the other. 
   As is evident from the foregoing description, the data transmission system and the cable of the first aspect of the invention has an advantageous effect that the data transmission system can be realized wherein the installing positions of the open drain type output section and the pull-up type resistor are moved to the cable while the combination thereof is kept, thereby rendering a parasitic capacitance small so that data can be transmitted at high speed without being bound by the counterpart&#39;s power supply voltage. 
   The data transmission system and the cable of the second aspect of the invention has an advantageous effect that the data transmission system can be realized wherein the data transmission system can be familiar with existing electronic equipment by limiting the improved section of the two-way transmitting circuit to one side of the connector so that data can be transmitted at higher speed without being bound by the counterpart&#39;s power supply voltage.