Patent Publication Number: US-2011055615-A1

Title: Method of and device for detecting cable connection

Description:
This application is a divisional of application Ser. No. 11/447,898, filed Jun. 7, 2006, which is a divisional of application Ser. No. 09/971,674, filed Oct. 9, 2001. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method of and device for detecting wire connection between a personal computer and a peripheral device by the use of the technology of Universal Serial Bus (“USB”). 
     BACKGROUND OF THE INVENTION 
       FIG. 6  is a block diagram showing a connection between the personal computer  1007  and the conventional detector  1001 . The personal computer  1007  comprises the root hub  1005  and the plug  1004 . The root hub  1005  is a host for communication using the USB. The root hub  1005  and the plug  1004  are connected through the power line VBUS and the resistance R 2 . Electric potential VBUS is supplied to the peripheral device from the personal computer through a power line. 
     The detector  1001  comprises the level conversion and protection circuit  1002 , MCU  1003 , plug  1009 , and the resistance R 1 . The MCU  1003  and the plug  1009  are connected through the USB communication line transmitting electrical potential for a differential signal of a D+ voltage level, and the USB communication line transmitting electrical potential for a differential signal of a D− voltage level. The resistance R 1  is connected between the MPU  1003  and the USB communication line transmitting D− electrical potential. The resistance R 1  transmits an output VREG of a regulator built in the MCU  1003 . The plug  1004  of the personal computer  1007  and the plug  1009  of the detector  1001  are connected through the cable  1006 . 
     Potential VBUS from the personal computer  1007  is applied to the level conversion and protection circuit  1002  through the plugs  1004  and  1009 . When the potential VBUS is received, the level conversion and protection circuit  1002  outputs the VBUS detection signal to the MCU  1003 . 
     In the conventional detector  1001  the level conversion and protection circuit  1002  is provided outside the MCU  1003 . Thus, reception of potential VBUS is detected in this level conversion and protection circuit  1002  that is an external circuit with respect to the MPU  1003 . The MCU  1003  detects connection of the detector  1001  and the personal computer  1007  based on the VBUS detection signal output by the level conversion and protection circuit  1002 . Thus, in the conventional detector  1001  the level conversion and protection circuit  1002  is required and therefore it is difficult to reduce the size of the circuit. 
     Some times the detector is provided with a built in battery power supply and this battery is charged using the potential received from the personal computer. However, in such a detector it is difficult to perform fine detection of the connection, therefore, more circuitry is required to be provided. Therefore, there is a problem that it is difficult to reduce the size of the circuit. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide an intelligent and small-sized detector that consumes less power. 
     The detector according to one aspect of this invention comprises a plug for connecting the detector to the personal computer through a cable; a battery power supply which outputs a predetermined constant electrical potential; and a Micro Control Unit which receives a specific electrical potential from the personal computer through the plug and cable, and receives the constant electrical potential from the battery power supply. 
     The detector according to another aspect of this invention comprises a plug for connecting the detector to the personal computer through a cable; a battery power supply which outputs a predetermined constant electrical potential; an oscillator which outputs an oscillation signal; and a Micro Control Unit which receives a specific electrical potential from the personal computer through the plug and cable, receives the constant electrical potential from the battery power supply, and receives the oscillation signal from the oscillator. 
     Other objects and features of this invention will become apparent from the following description with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a detector according to a first embodiment; 
         FIG. 2  is a block diagram of a detector according to a second embodiment; 
         FIG. 3  is a block diagram of a detector according to a third embodiment; 
         FIG. 4  is a block diagram of a detector according to a fourth embodiment; 
         FIG. 5  is a block diagram of a detector according to a fifth embodiment; and 
         FIG. 6  is a block diagram showing a connection between  10  a personal computer and a conventional detector. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of a detector according to the present invention will be explained below with reference to the accompanying drawings. 
       FIG. 1  is a block diagram of the detector  1  according to a first embodiment of the present invention. The detector  1  comprises the MCU  3 , the battery power supply  7 , and the plug  9 . The battery power supply  7  supplies a predetermined  20  constant electrical potential to the MCU  3 . The plug  9  supplies a specific electrical potential to the MCU  3 . 
     The MCU  3  comprises the USB function circuit  5 , the CPU and peripheral circuit  6 , and the detection circuit  8 . Moreover, the MCU  3  comprises a VCC terminal for input of a VCC level signal from the battery power supply  7 , VSS terminal which is connected to the plug  9  for transmission of a standard level VSS (usually, earth electrical potential, and hereinafter, called as VSS), D+ terminal which is connected to the plug  9  for transmission of a D+ electric level, and a D− terminal which is connected to the plug  9  for transmission of a D− electric level. 
     The MCU  3  comprises a VREG terminal for transmission of output VREG of a regulator built in the USB function circuit  5 , and a VBUS terminal which is connected to the plug  9  for transmission of VBUS (electrical potential supplied form the personal computer). 
     The USB function circuit  5  is connected to the VCC terminal, VSS terminal, D+ terminal, D− terminal, VREG terminal, and the VBUS terminal. The CPU and peripheral circuit  6  is connected to the VCC and VSS terminals. The CPU and peripheral circuit  6  performs on-off control of the USB function circuit  5  based on the output of the detection circuit  8 . The detection circuit  8  is connected to the VBUS terminal, and the CPU and peripheral circuit  6 . The resistance R 1  whose one terminal is connected to the VREG terminal, and the other terminal is connected to a USB communication line for transmission of the D− electrical potential is provided. The D− electrical potential is pulled up by the resistance R 1  at the VREG electrical potential in the case of low rate USB communication. 
     Although not shown here, the detector  1  is connected to a personal computer through the plug  9 , cable, and a plug in the personal computer is the same manner as explained with reference to the conventional detector. 
     The D− electrical potential is pulled up to VREG X (R 2 /(R 1 +R 2 )) V and the D+ electrical potential is pulled down by the resistance R 2 , as there is no output by the resistance R 1  and the resistance R 2  of the personal computer together with the MCU  3  and the root hub of the personal computer in the case of no communication. 
     Operations of the detector  1  will be described below. When the cable for connecting the detector  1  and the personal computer is connected to the plug  9 , potential VBUS which is received from the personal computer is applied to the USB function circuit  5  and the detection circuit  8 . 
     The detection circuit  8  supplies the potential VBUS to the CPU and peripheral circuit  6 . The detection circuit  8  monitors the voltage level of VBUS supplied through the cable. The CPU and peripheral circuit  6  outputs an Enable signal for ON operation of the USB function circuit  5  so as to perform USB communication. 
     The USB function circuit  5  after the ON operation outputs the VREG electrical potential of the output of the built-in regulator. The VREG electrical potential is applied to the D− terminal while the D− electrical potential of the USB communication line is pulled up by the resistance R 1 . 
     The detection circuit  8  outputs a signal having a low logical level (“L”) when the potential VBUS is Hi-Z and outputs a signal having high logical level (“H”) when the potential VBUS is the specific electrical potential (for example, 5 V) to the CPU and peripheral circuit  6 . In other words, the detection circuit  8  shall output a “L” signal when the detector and the personal computer are not connected to each other, because, in this case the potential VBUS will be equal to Hi-Z. On the other hand, the detection circuit  8  shall output a “H” signal when the detector and the personal computer are connected to each other, because, in this case the potential VBUS will be equal to the specific electrical potential. 
     Thus, whether the detector and the personal computer are connected to each other can be detected by the CPU and peripheral circuit  6  based on the changes in the voltage level of VBUS supplied from the detection circuit  8 . Accordingly, the MCU  3  functions as a communication controller using the USB between the detector  1  and the personal computer. 
     According to the first embodiment, more intelligent connection detection using the MCU, compared with that of a conventional detector, may be realized by provision of the MCU provided with the detection circuit. 
     Moreover, the MCU has an advantage that the MCU eliminate a special circuit, which has been conventionally required for detection, as the MCU may have a control function as a peripheral device (not shown). 
     When the detector  1  and the personal computer are not connected to each other, the peripheral device is activated based on the built in battery power supply. In this case, the potential VBUS is not input into the USB function circuit. The USB function circuit may be made to stop its operation when the potential VBUS is not received, which shall lead to reduced power consumption. The USB function circuit may be made to restart its operation when the detector and the personal computer are once more connected to each other. Moreover, the MPU  3  may be made to charge the battery power supply using the potential VBUS. 
       FIG. 2  is a block diagram of a detector  11  according to a second embodiment of the present invention. The detector  11  comprises MCU  13 , battery power supply  17  for supplying of predetermined electrical potential to the MCU  13 , and the plug  19  transmitting specific electrical potential to the MCU  13 . 
     The MCU  13  comprises the USB function circuit  15 , CPU and peripheral circuit  16 , and the A-D converter  18 . Moreover, the MCU  13  comprises a VCC terminal for input of a VCC level signal from the battery power supply  17 , VSS terminal which is connected to the plug  19  for transmission of a standard level VSS, D+ terminal which is connected to the plug  19  for transmission of a D+ electric level; and a D− terminal which is connected to the plug  19  for transmission of a D− electric level. The MCU  13  also includes a VREG terminal for transmission of an output VREG of a regulator built in the USB function circuit  15  and a VBUS terminal which is connected to the plug  19  for transmission of VBUS (electrical potential supplied from the personal computer). 
     The USB function circuit  15  is connected to the VCC terminal, VSS terminal, D+ terminal, D− terminal, VREG terminal, and the VBUS terminal. The A-D converter  18  is connected to the VCC terminal, VSS terminal, and the D− terminal. The A-D converter  18  performs conversion of the D− electrical potential to a digital value for transmission to the CPU and peripheral circuit  16 . The CPU and peripheral circuit  16  is connected to the VCC and VSS terminals. The CPU and peripheral circuit  16  performs on-off control of the USB function circuit  15  based on the output of the A-D converter  18 . The resistance R 1  whose one terminal is connected to the VREG terminal, and the other terminal to a USB communication line for transmission of the D− electrical potential is provided. The D− electrical potential is pulled up at the VREG electrical potential in the case of low rate USB communication. 
     Although not shown here, the detector  11  is connected to a personal computer through the plug  19 , cable, and a plug in the personal computer is the same manner as explained with reference to the conventional detector. 
     Moreover, the D− electrical potential is pulled up to VREGX (R 2 /(R 1 +R 2 )) V and the D+ electrical potential is pulled down by the resistance R 2 , as there is no output by the resistance R 1  and the resistance R 2  of the personal computer together with the MCU  13  and the root hub of the personal computer in the case of no communication. 
     The detector  11  operates as follows. The D− electrical potential of the USB communication line is divided by the resistance R 1  and the resistance R 2  provided in the personal computer, in a state the cable is connected to the plug  19  and there is no communication. 
     The divided electrical potential is input to the A-D converter  18  as an A-D input. The A-D converter  18  outputs the VBUS detection signal to the CPU and peripheral circuit  16 . 
     The CPU and peripheral circuit  16  outputs the Enable signal to the USB function circuit  15  to perform on-off operation of the USB function circuit  15 , and the USB function circuit  15  outputs the output VREG of the built-in regulator. 
     The VREG electrical potential is transmitted to the D− terminal while the D− electrical potential of the USB communication line is pulled up by the resistance R 1 . 
     When the detector  11  and the personal computer are not connected to each other, the D− electrical potential becomes equal to the output VREG of the regulator. Accordingly, whether the detector and the personal computer are connected to each other can be detected based on the detection of the difference in the D− electrical potential between the connection state of the cable and the non-connection state of the cable. That is, the difference in the digital values caused by the connection/non-connection states of the cable may be used as detection unit. 
     According to the second embodiment, the similar advantages to those of the first embodiment may be expected by provision of the MCU comprising the A-D converter, and, if the A-D converter is essentially required as a function of a personal computer peripheral device, common use of the converter may be advantageously realized. 
       FIG. 3  is a block diagram of a detector  31  according to a third embodiment of the present invention. The detector  31  comprises the MCU  33 , battery power supply  37  for supplying of predetermined electrical potential to the MCU  33 , and the plug  39  transmitting specific electrical potential to the MCU  33 . 
     The MCU  33  comprises the USB function circuit  35 , CPU and peripheral circuit  36 , and the ring oscillator  38 . Furthermore, the MCU  33  comprises a VCC terminal for input of a VCC level signal from the battery power supply  37 , VSS terminal which is connected to the plug  39  for transmission of a standard level VSS, D+ terminal which is connected to the plug  39  for transmission of a D+ electric level, and a D− terminal which is connected to the plug  39  for transmission of a D− electric level. The MCU  33  also includes a VREG terminal for transmission of output VREG of a regulator built in the USB function circuit  35 , and a VBUS terminal which is connected to the plug  39  for transmission of VBUS (electrical potential supplied from the personal computer). 
     The USB function circuit  35  is connected to the VSS terminal, VSS terminal, D+ terminal, D− terminal, VREG terminal, and the VBUS terminal. The CPU and peripheral circuit  36  is connected to the VCC and VSS terminals. The CPU and peripheral circuit  36  performs on-off control of the USB function circuit  35  based on the output of the ring oscillator  38 . The ring oscillator  38  is connected to the VBUS and VSS terminals. 
     The resistance R 1  whose one terminal is connected to the VREG terminal and the other terminal is connected to a USB communication line for transmission of the D− electrical potential is provided. The resistance R 1  pulls up the D− electrical potential at the VREG electrical potential in the case of low rate USB communication. 
     Although not shown here, the detector  31  is connected to a personal computer through the plug  39 , cable, and a plug in the personal computer is the same manner as explained with reference to the conventional detector. 
     Moreover, the D− electrical potential is pulled up to VREGX (R 2 /(R 1 +R 2 )) V and the D+ electrical potential is pulled down by the resistance R 2 , as there is no output by the resistance R 1  and the resistance R 2  of the personal computer together with the MCU  33  and the root hub of the personal computer in the case of no communication. 
     The detector  31  operates as follows. Potential VBUS functions as a power supply of the ring oscillator  38  for oscillation in a state where the cable is connected to the plug  39 . The ring oscillator  38  outputs the VBUS detection signal to the CPU and peripheral circuit  36 . The CPU and peripheral circuit  36  outputs the Enable signal to the USB function circuit  35 , and the USB function circuit  35  outputs the output VREG of the built-in regulator. 
     When the detector  31  and the personal computer are not connected to each other, the ring oscillator  38  does not oscillate. Accordingly, whether the detector  31  and the personal computer are connected to each other can be detected based on monitoring of the difference in the oscillation output of the ring oscillator  38  between under a connection state and under a non-connection state of the cable. 
     According to the third embodiment, the similar advantages to those of the first embodiment may be expected by provision of the MCU comprising the ring oscillator. 
       FIG. 4  is a block diagram of a detector  51  according to a fourth embodiment of the present invention. The detector  51  comprises the MCU  53 , battery power supply  57  for supplying of predetermined electrical potential to the MCU  53 , plug  59  transmitting specific electrical potential to the MCU  53 , and the oscillator (for example, ceramic or crystal-oscillation circuit, and, hereinafter, called as an oscillator)  61  for input/output of an oscillation signal to/from the MCU  53 . 
     The MCU  53  comprises the USB function circuit  55 , CPU and peripheral circuit  56 , oscillation circuit  58 , and the counter  60  for counting of the oscillation output from the oscillation circuit  58 . Furthermore, the MCU  53  comprises a VCC terminal for input of a VCC level signal from the battery power supply  57 , D+ terminal which is connected to the plug  59  for transmission of a D+ electric level, and a D− terminal which is connected to the plug  59  for transmission of a D− electric level. The MCU  53  also comprises a VREG terminal for transmission of an output VREG of a regulator built in the USB function circuit  55 , and a VBUS terminal which is connected to the plug  59  for transmission of VBUS (electrical potential supplied from the personal computer) In addition, the MCU  53  comprises a XIN terminal, and a XOUT terminal for transmission of an oscillation signal which is input to the oscillation circuit  58  from the oscillator  61  and vice versa. 
     The USB function circuit  55  is connected to the D+ terminal, D− terminal, VREG terminal, and the VBUS terminal. The oscillation circuit  58  is connected to the VBUS terminal, XIN terminal, and the XOUT terminal. The oscillation circuit  58  performs transmission of the oscillation output to the counter  60 . The CPU and peripheral circuit  56  is connected to the VCC terminal. The CPU and peripheral circuit  56  performs on-off control of the USB function circuit  55  based on the output of the counter  60 . 
     The resistance R 1  whose one terminal is connected to the VREG terminal, and the other terminal is connected to a USB communication line for transmission of the D− electrical potential is provided. The resistance R 1  pulls up the D− electrical potential at the VREG electrical potential in the case of low rate USB communication. 
     Although not shown here, the detector  51  is connected to a personal computer through the plug  59 , cable, and a plug in the personal computer is the same manner as explained with reference to the conventional detector. 
     Moreover, the D− electrical potential is pulled up to VREGX (R 2 /(R 1 +R 2 )) V and the D+ electrical potential is pulled down by the resistance R 2 , as there is no output by the resistance R 1  and the resistance R 2  of the personal computer together with the MCU  53  and the root hub of the personal computer in the case of no communication. 
     The detector  51  operates as follows. Potential VBUS is supplied to the oscillation circuit  58  for oscillation in a state where the cable is connected to the plug  59 . Oscillation output from the oscillation circuit  58  is input to the counter  60  which outputs a detection signal to the CPU and peripheral circuit  56  after a predetermined number of counts. That is, the CPU and peripheral circuit  56  may detect the connection state of the cable by overflow of the counter  60 . The CPU and peripheral circuit  56  outputs the Enable signal to the USB function circuit  55 , and the USB function circuit  55  outputs the output VREG of the built-in regulator. 
     When the detector  51  and the personal computer are not connected to each other, the oscillation circuit  58  does not oscillate. Accordingly, whether the detector  51  and the personal computer are connected to each other can be detected by confirmation, with the CPU and peripheral circuit  56 , of a counting state where oscillation output from the oscillation circuit  58  under the connection state of the cable is counted by a counter  60 . 
     According to the fourth embodiment, the similar advantages to those of the first embodiment may be expected by provision of an MCU comprising the oscillation circuit for transmission of an input/output from/to the oscillator; and a counter for input from the oscillation output from an oscillation circuit. 
       FIG. 5  is a block diagram of a detector  71  according to a fifth embodiment of the present invention. The detector  71  comprises MCU  73 , battery power supply  77  for supplying of predetermined electrical potential to the MCU  73 , plug  79  transmitting specific electrical potential to the MCU  73 , plug  79  for transmission of specific electrical potential to the MCU  73 , and the oscillator  81 . 
     The MCU  73  comprises the USB function circuit  75 , CPU and peripheral circuit  76 , oscillation circuit  78 , counter  80  for counting of the oscillation output from the oscillation circuit  78 , and the PLL circuit  82  for generation of a clock for operations of the USB function circuit  75  by frequency multiplication of the oscillation output from the oscillation circuit  78 . Furthermore, the MCU  73  comprises a VCC terminal for input of a VCC level signal from the battery power supply  77 , D+ terminal which is connected to the plug  79  for transmission of a D+ electric level, and a D− terminal which is connected to the plug  79  for transmission of a D− electric level. The MCU  73  also comprises a VREG terminal for transmission of the output VREG of a regulator built in the USB function circuit  75 , and a VBUS terminal which is connected to the plug  79  for transmission of VBUS (electrical potential supplied from the personal computer). In addition, the MCU  73  comprises a XIN terminal, and a XOUT terminal for transmission of an input/output signal which is input to the oscillation circuit  78  from the oscillator  81  and vice versa. 
     The oscillation circuit  78  is connected to the VBUS terminal, XIN terminal and the XOUT terminal. The oscillation circuit  78  performs transmission of the oscillation output to the counter  80  and the PLL circuit  82 . The USB function circuit  75  is connected to the D+ terminal, D− terminal, VREG terminal, and the VBUS terminal. The PLL circuit  82  supplies a clock to the USB function circuit  75 . 
     The CPU and peripheral circuit  76  is connected to the VCC terminal. The CPU and peripheral circuit  76  performs on-off control of the USB function circuit  75  based on the output of the counter  80 . 
     The resistance R 1  whose one terminal is connected to the VREG terminal and the other terminal is connected to a USB communication line for transmission of the D− electrical potential is provided. The resistance R 1  pulls up the D− electrical potential at the VREG electrical potential. 
     Although not shown here, the detector  71  is connected to a personal computer through the plug  79 , cable, and a plug in the personal computer is the same manner as explained with reference to the conventional detector. 
     Moreover, the D− electrical potential is pulled up to VREGX (R 2 /(R 1 +R 2 )) V and the D+ electrical potential is pulled down by the resistance R 2 , as there is no output by the resistance R 1  and the resistance R 2  of the personal computer together with the MCU  73  and the root hub of the personal computer in the case of no communication. 
     The detector  71  operates as follows. Potential VBUS is supplied to the oscillation circuit  78  for oscillation in a state where the cable is connected to the plug  79 . Oscillation output from the oscillation circuit  78  is input to the counter  80  which outputs a detection signal to the CPU and peripheral circuit  76  after a predetermined number of counts. The PLL circuit  82  that outputs a clock for operations to the USB function circuit  75  by input and frequency multiplication of the oscillation output from the oscillation circuit  78 . The CPU and peripheral circuit  76  outputs the Enable signal to the USB function circuit  75 , and the USB function circuit  75  outputs the output VREG of the built-in regulator. 
     When the detector  71  and the personal computer are not connected to each other, the oscillation circuit  78  does not oscillate. Accordingly, whether the detector  71  and the personal computer are connected to each other can be detected by confirmation, with the CPU and peripheral circuit  76 , of a counting state where oscillation output from the oscillation circuit  78  under the connection state of the cable is counted by a counter  80 . 
     According to the fifth embodiment, more intelligent connection detection, compared with that of the fourth embodiment, maybe realized by provision of the MCU provided with the oscillation circuit for transmission of the input/output form the oscillator; the counter for input of the oscillation output from the oscillation circuit; and the PLL circuit for generation of a clock for operations of the USB function circuit by frequency multiplication of the oscillation output from the oscillation circuit. 
     Moreover, when a clock for operations of the USB function circuit is commonly used as the oscillation output from the oscillation circuit, a specially dedicated oscillation circuit may be eliminated, as only a counter is required for a circuit functioning only as detection unit. 
     In addition, there is also an advantage that the clock for operations of the USB function circuit is commonly used as the oscillation circuit for detection of whether the detector  71  and the personal computer are connected to each other. 
     According to a sixth embodiment of the present invention, the detector comprises a MCU that includes a comparator instead of the A-D converter shown in  FIG. 2 . Other configuration is the same as that shown in  FIG. 2 . However, the threshold for the comparator is assumed to be controlled enough to detect the difference of the D− electrical potential between a connection state and a non-connection state of the cable. 
     Whether the detector according to the sixth embodiment and the personal computer are connected to each other can be detected by detection, with the inverter, of the difference in the D− electrical potential between the connection state and the non-connection state of the cable. 
     Thus, according to the sixth embodiment, more intelligent connection detection, than that of the second embodiment, may be realized by provision of the MCU comprising the comparator. The comparator has a simpler configuration as compared to the A-D converter, therefore, cost reduction becomes possible, and circuit becomes simple. 
     According to a sixth embodiment of the present invention, the detector comprises a MCU that includes an inverter instead of the A-D converter shown in  FIG. 2 . Other configuration is the same as that shown in  FIG. 2 . However, the threshold for the inverter is assumed to be designed enough to detect the difference of the D− electrical potential between a connection state and a non-connection state of the cable. 
     Whether the detector according to the seventh embodiment and the personal computer are connected to each other can be detected by detection, with the inverter, of the difference in the D− electrical potential between the connection state and the non-connection state of the cable. 
     According to the seventh embodiment, more intelligent connection detection, than that of the second embodiment, may be realized by provision of the MCU comprising the inverter. 
     Moreover, the detection function may be realized by using an inverter with appropriately adjusted threshold (enough to detect the changes in the D− electrical potential), that is, by a simpler configuration than that of a comparator according to the sixth embodiment. 
     As explained above, according to the detector of one aspect of this invention, intelligent and small-sized detector with low power consumption is obtained. Furthermore, a dedicated circuit for detection that is used conventionally is not required. 
     Also, the MCU is provided with the control function as a peripheral device. The peripheral device is activated using built-in battery and the operation of the USB function circuit is stopped when the detector and the personal computer are not connected, thereby achieving reduction in the power consumption. Furthermore, when the detector and the personal computer are connected, the operation of the USB function circuit is restarted, and the battery is charged by the potential from the personal computer. 
     Furthermore, a A-D converter is provided which may be commonly used if the peripheral device requires A-D conversion. The A-D converter may be replaced with a comparator. The comparator has a simpler configuration as compared to the A-D converter. Furthermore, the A-D converter may be replaced with an inverter. The inverter has a simpler configuration as compared to the A-D converter. 
     According to the method of another aspect of this invention, fine detection of the connection with low power consumption may be efficiently performed. 
     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.