Abstract:
A USB connection-detection circuitry and the operation method of the same are disclosed. The circuitry includes a transmitting circuit and a detecting circuit. The transmitting circuit contains a pair of differential signal lines, a pair of pull-down resistors and a pair of pull-up resistors wherein one pull-down resistor and one pull-up resistor are connected to the same differential signal line with their own individual switches. A power-related signal supplied by a power-supply system is received by the transmitting circuitry and transmitted through a differential signal line. Then, the power-related signal is grounded via a pull-down resistor. The detecting circuit is utilized to detect the power-related signals, which flow through the differential lines. When a device is connected to this connection-detection circuitry with a USB cable, the differential signal lines of the USB cable are connected with the differential signal lines of this circuitry. This results in the variation of the power-related signals, which are connected to the ground through the pull-down resistors originally. Therefore, by comparing the difference of the power-related signals before and after the connection, the connection-detection circuitry is able to automatically identify the mode of the device, which connects to the circuitry.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates generally to a circuitry and its operating methods, more particularly to a Connection-detection circuitry and its operating methods used in a USB system.  
         DESCRIPTION OF THE RELATED ART  
         [0002]    Universal Serial Bus (USB) is a new interface proposed by several major computer manufactures to solve the inextricable problems experienced when installing and extending a conventional computer system and its peripheral equipments. Under this system, all peripherals can communicate with the host computer through the same interface, i.e., a USB bus. Moreover, one of its distinguishing features is that all USB peripherals are provided with “plug and play” function. That is to say, it is no longer a necessity to switch off the host computer or to install the drivers prior the installation or removing of such devices.  
           [0003]    In accordance with the USB specification, each USB system is consist of three elements: a USB host, a USB inter-connection interface, and a USB device. There is only one USB host in a USB system and is often constructed within the host computer. USB devices can be classified as a USB function device and a USB hub. USB function devices are referred to computer peripheral devices such as a keyboard, a mouse or a printer, etc. and each USB function device is connected to a USB host through a USB inter-connection interface. USB hubs can expand a single connection port to be multiple connection ports and enable a plurality of USB function devices to be connected to the same USB bus.  
           [0004]    With reference to FIG. 1, a schematic diagram is drawn to illustrate the connecting method of a USB system. As shown in the figure, a plurality of USB functional devices and USB hubs are connected to the host  10  with a tiered star topology. A root hub  11  is located at the base of the USB host  10  and provides two connection ports  12  and  13  which are used to connect a USB hub  14  or a function device  15 . Each USB hub  14  provides several connection ports to which the plural USB function devices  15 , 17  and USB hubs  16  can be connected. In this way, a maximum of 127 function devices can be attached to a host.  
           [0005]    When a USB device is attached to a USB hub, its presence can be detected by the USB hub automatically. The hub informs the USB host which it is connected to that a “new device” is attached to the bus. After a succession of data transmission, the USB device is then connected to the USB bus and start responding to the requests of the host computer or the user, to perform the build-in functions thereof. In order to detect the presence of new devices, a set of connection-detection circuitry built in the USB hub and the USB devices separately are utilized by the USB hub to detect the connection and removing of the USB devices.  
           [0006]    Refer to the FIG. 2, a set of USB Connection-detection circuitry built in a conventional USB hub device (or a host) and a conventional USB device is shown in the figure. The connection-detection circuitry includes an up stream detection circuitry  200 , which is constructed in the USB hub device  20  (or a host), and a down stream detection circuitry  300 , which is constructed in the USB device  30 .  
           [0007]    As shown in the figure, the USB hub device  20  and the USB device  30  are connected to each other with a USB cable  40 . The USB cable  40  includes four wires: two power lines  401 ,  402  (VCC and GND), and two differential signal lines  403 ,  404  (i.e., the differential signal line  403  is referred to a D+ differential signal line while the differential line  404  is referred to a D− differential signal line). One terminal of the USB cable  40  is connected to the USB hub device  20 , and the other one is connected to the USB device  30 . Inside the USB hub device  20 , a pair of differential signal lines  203 ,  204  whose terminals are connected to the USB transceiver  205  which constructed in the USB hub device  20  are used to connect to the Differential signal lines  403 ,  404  (D+ and D−) of the USB cable  40 . Further, a pair of pull-down resistor  206 ,  207  are constructed in the USB hub device  20 , wherein the pull-down resistor  206  is connected to the differential signal line  203 , and the pull-down resistor  207  is connected to the differential signal line  204 . The up stream detection circuitry  200  of the USB hub device  20  is constructed by the differential signal lines  203 ,  204 , pull-down resistors  206 ,  207 , and a voltage detector  220 . Meanwhile, a pair of differential signal lines  303 ,  304  are also constructed in the USB device  30  and used to connect to the differential signal lines  403 ,  404  (D+ and D−) of the USB cable  40 . The other terminals of the differential signal lines  303  and  304  are both connected to the USB transceiver  305  of the USB device  30 .  
           [0008]    Furthermore, a pull-up resistor  308  is constructed inside the USB device  30  and connected to the differential signal line  303  when the USB device is a Full/High Speed USB device, i.e., a device whose data transmission rate is 12/480 MB per second, such as a printer or a microphone. The differential signal line  303  is then used to connect to the D+ differential signal line  403  of the USB cable  40 .  
           [0009]    On the other hand, a pull-up resistor  309  is constructed inside the USB device  30  and connected to the differential signal line  304  when the USB device  30  is a Low Speed USB device, i.e., a device whose data transmission rate is 1.5 Mb per second, such as a mouse or a keyboard. The Differential Signal Line  304  is then used to connect to the D− differential signal line  404  of the USB cable  40 .  
           [0010]    No matter it is a high speed or a low speed device, the USB device  30  is equipped with a down stream detection circuitry  300  which is constructed by the differential signals line  303 ,  304  and a pull-up resistor  308  or  309 . The down stream detection circuitry  300  is used to connect to the up stream detection circuitry  200  via the USB cable  40  and enables the USB hub device  20  to perform the connecting or removing detection of the USB devices.  
           [0011]    Herein below are descriptions about the operation methods of the connection-detection circuitry.  
           [0012]    First, the differential signal lines  203 ,  204  which are constructed in the USB hub device  20  and used to connect to the D+ and D− differential signal lines  403 ,  404  are connected to a ground voltage through the pull-down resistors  206 ,  207  before connecting to the USB device  30 .  
           [0013]    When the USB device  30  is connected to the USB hub device  20  via the USB cable  40 , a voltage of 5V is supplied from the USB hub device  20  to the USB device  30  through a VCC power line  401  within the USB cable  40 . Then a voltage of 3.3V is provided to the pull-up resistor  308  or  309  by the circuitry (not shown) inside the USB device  30  utilizing the power supplied by the USB hub device  20 . If the USB device is a High-Speed device, a voltage of 3.3V is provided to the pull-up resistor  308  and a potential difference is generated between the two terminals of the differential signal line  403  of the USB cable  40 . The voltage level of the differential line  203  is detected by the voltage detector  220  of the USB hub device  20 . Therefore, the attached device is identified by the USB hub device  20  as a High-Speed device according to the voltage change. Besides, if the USB device  30  is a Low-Speed device, a voltage of 3.3V is provided to the pull-up resistor  309  and a potential difference is generated between the two terminals of the differential signal line  404  of the USB cable  40 . The voltage level of the differential line  204  is detected by the voltage detector  220  of the USB hub device  20 . Therefore, the attached device is identified by the USB hub device  20  as a Low-Speed device according to the voltage change.  
           [0014]    On the other hand, if a USB device  30  which is originally connected to the USB hub device  20  is removed from the bus, the disconnection of the USB device  30  also can be detected by the USB hub device  20  with the connection-detection circuitry.  
           [0015]    The above descriptions are related to a connection-detection circuitry constructed in a conventional USB hub device (or host) and a conventional USB device. A drawback of the connection-detection circuitry mentioned above is that it is designed with USB standard specifications, that is, the devices which are connected to each other through the connection-detection circuitry must maintain a host-device relationship in order to fulfill the tiered star topology of a USB bus. Thus, under such circumstances, a USB function device only can be connected to a USB hub device or a USB host device and cannot be connected to another USB function device. As a result, the data transmission directly from one USB function device to another USB function device is forbidden.  
         SUMMERY OF THE INVENTION  
         [0016]    Therefore, one object of the invention is to provide a circuitry, which enables a USB device to connect to a USB device or a USB host arbitrarily.  
           [0017]    Further, another object of the invention is to provide an operation method of the circuitry such that a USB device containing such circuitry is able to identify the device type of a USB device or a USB host to which it is connected.  
           [0018]    According to the invention, the circuitry includes a transmitting circuit and a detecting circuit. The transmitting circuit is used to receive a first power-related signal from a power supply system, and the detection circuit is used to detect the change of the first power-related signal. The transmitting circuit includes a first differential signal line, a first pull-down resistor, and a first switching element. Therein, the first power-related signal is transmitted through the first differential signal line and is grounded via the first pull-down resistor. The first switching element is disposed between the pull-down resistor and the first differential signal line and is used to switch the connection between the first differential signal line and the first pull-down resistor.  
           [0019]    The transmitting circuit further includes a first power line, a second switching element, a first pull-up resistor, and a third switching element. Therein, the first power line is used to transmit a second power-related signal received from the power supply system to a power line of the USB cable, and is connected to the power supply system via the second switching element. The first pull-up resistor is connected to the first differential signal line via the third switching element.  
           [0020]    The detecting circuit of the circuitry includes a timer which is used to calculate a period of time.  
           [0021]    In addition, the circuitry further includes a first power supply system as the power supply system for supplying a plurality of power-related signals.  
           [0022]    According to this invention, the present invention also provides a operation method of the circuitry and the method includes the following steps: receiving a first power-related signal from a power supply system; connecting the first power-related signal to a ground voltage through a pull-down resistor; receiving a second power related signal from the power supply system when a device is connected to the circuitry with a USB cable and transmitting the second power related signal to a power line of the USB cable before a differential signal line of the USB cable is connected to a conductive line which the first power related signal is transmitted through; detecting the change of the first power related signal before and after connecting to the device; and determining whether or not to stop receiving the first and the second power related signal from the power supply system according to the change of the first power related signal detected.  
           [0023]    Therein, when the receiving of the first and the second power related signals are stopped, a forth power related signal is supplied by the circuitry to the differential signal line of the USB cable utilizing a third power related signal if the third power related signal is received by the circuitry from the power line of the USB cable during a time period.  
           [0024]    On the other hand, if the third power related signal is not received by the circuitry from the power line of the USB cable after the period of time, the first and second power related signal is received from the power supply system again, and the first power related signal is connected to a ground voltage through the pull-down resistor and the second power related signal is transmitted to the power line of the USB cable.  
         DESCRIPTION OF PREFERRED EMBODIMENTS  
         [0025]    What followed is the detailed descriptions of methods and preferred embodiments of the invention to achieve the above mentioned objectives.  
         Manual Switch Mode  
         [0026]    Refer to FIG. 3, a connection-detection circuitry of the first embodiment according to the present invention is shown in the figure. The Connection-detection circuitry  500  includes a pair of differential signal lines  503 ,  504 , a pair of pull-down resistor  506 ,  507 , a pair of pull-up resistor  508 ,  509 , a power supply system  510 , and a set of manual switching elements  511 . Wherein, the differential signal line  503  is used to connect to a D+ differential signal Line  403  of a USB cable  40  while the differential signal line  504  is used to connect to a D− differential signal line  404  of the USB cable  40 . The connection-detection circuitry  500  of this embodiment is a manual-switch mode circuitry.  
           [0027]    If a USB “Devicehost” device  50  containing such connection-detection circuitry  500  is to be connected to a USB host or a USB hub device, the user can use a set of manual-switch elements  511  to set the USB Devicehost device  50  into “Device-Mode” before the connection. Under Device-Mode, the pull-down resistors  506 , 507  and the power supply system  510  are disconnected by the manual-switch elements  511 . When the Devicehost device  50  is a High-Speed USB device, a pull-up resistor  508  is connected to a differential signal line  503  and the other pull-up resistor  509  is disconnected. On the other hand, if the Devicehost device  50  is a Low-Speed USB device, a pull-up resistor  509  is connected to differential signal line  504  and the other pull-up resistor  508  is disconnected.  
           [0028]    When the Devicehost device  50  is connected to a USB host or a USB hub device, a voltage of 5V is supplied from the USB host/hub device to the USB Devicehost device  50  through the USB cable  40 . The following detection steps are the same with those of the USB device  30  connecting to the USB hub device  20  mentioned above.  
           [0029]    If the Devicehost device  50  is to be connected to another USB function device, the user can use the manual-switch elements  511  to set the Devicehost device  50  into “Host-Mode”. Under Host-Mode, the pull-up resistors  508 , 509  are disconnected by the manual-switch elements  511 . Meanwhile, the pull-down resistors  506 ,  507  are connected to the differential signal lines  503 ,  504  separately and the power supply system  510  is also connected to a power line (not shown) constructed in the Devicehost device  50 . Therein, the power line is used to connect to a power line  401  of the USB cable  40 . When the Devicehost device  50  is connected to a USB function device, a voltage of 5V is supplied from the Devicehost device  50  to the USB function device through the USB cable  40 . Then, a voltage of 3.3V is supplied to the pull-up resistor connected to the differential signal line  403  or  404  depending on the device type of the USB function device (High-Speed or Low-Speed) by utilizing the power supplied by the Devicehost device  50 . A potential difference is then generated between the two terminals of the differential signal line  403  or  404 . Therefore, the device type of the USB function device can be identified by the Devicehost device  50  according to the voltage change of the differential signal line  503  or  504  and the connection-detection process of these two devices is completed.  
           [0030]    As described above, by simulating the connection-detection methods of a USB host or hub device with the Connection-detection circuitry  500 , the USB Devicehost  50  is connected to a USB function device. Thus, a USB Devicehost device of the invention is able to be connected to a USB function device with the “Host-Device” relationship of USB system and processes the data transmission between these two devices by utilizing the software and firmware constructed thereof. The problems which data can not be transmitted directly from one USB device to another USB device under the standard USB specification is solved.  
         Current-Detection Mode  
         [0031]    The “Current-Detection Mode” differs from the above-mentioned “Manual-Switch Mode” in that the type of the device to which the Devicehost device is connected, i.e., a USB host/hub device or a USB function device, is identified with a current change detected by the connection-detection circuitry inside the Devicehost device automatically. It is no longer required for the user to switch the mode of the Devicehost device whose a Current-Detection Mode connection-detection circuitry before the connection.  
           [0032]    With reference to FIG. 4 a  and  4   b , a connection-detection circuitry  600  of the second embodiment according to the invention is shown in the figures. The connection-detection circuitry  600  includes a pair of differential signal lines  603 ,  604 , a power line  611 , a ground line  612 , a pair of pull-down resistors  606 ,  607 , a pair of pull-up resistors  608 ,  609 , a power supply system  610 , and a current-detection circuit  620 . Wherein, the differential signal lines  603 ,  604  are used to connect to the D+ and D− differential signal line  403 ,  404  of the USB cable  40  ; while each of the pull-down resistors  606  and the pull-up resistor  608  is connected to the differential signal line  603  with a switching element, and each of the pull-down resistor  607  and the pull-up resistor  609  is connected to the differential line  604  with a switching element, separately. Further, a timer  621  is constructed in the current-detection circuit  620  and will be explained in details later. Besides, the power supply system  610  of the connection-detection circuitry  600  can be omitted and replaced with an external power supply system.  
           [0033]    The operation methods of Current-Detection mode are explained as follows.  
           [0034]    First, a current source is supplied from the power supply system  610  to each of the differential signal lines  603  and  604 , individually. Before any connection taking place, the currents Ip, Im transmitting through the pull-down resistors  606  and  607  are the same with the outputs of the current sources added to the differential signal lines  603 ,  604 .  
           [0035]    Then, refer to FIG. 4 a , the connection method between a Devicehost device  60  including a Current-Detection Mode connection-detection circuitry  600  and a USB host/hub device  20  is shown in the figure. When the Devicehost device  60  is connected to a USB host  20  (or a USB hub device), the output current of the current source added to the differential signal line  603  is transmitted through the pull-down resistor  606  of the Devicehost device  60  and the pull-down resistor  206  of the USB host  20 ; while the output current of the current source added to the differential signal lines  604  is transmitted through the pull-down resistor  607  of the Devicehost device  60  and the pull-down resistor  207  of the USB host  20 . Therefore, the currents Ip, Im transmitting through the pull-down resistors  606  and  607  are decreased. Assume that the currents Ip, Im transmitting through the pull-down resistors  606 ,  607  before connection are both “I” and the resistance of the pull-down resistors  606 ,  607  are both “Rpd”, then the currents Ip and Im running through the two pull-down resistors when the two devices  60 ,  20  are connected can be expressed by equation (1): 
             Ip=Im=I×Rpd/ ( Rpd+Rp )  equation (1) 
           [0036]    By measuring the currents Ip, Im transmitting through the pull-down resistors  606 , 607 , the connected device can be recognized as a USB host by the Devicehost device  60 . The Devicehost device  60  is then switched into “Device-Mode” automatically. Under Device-Mode, the connection between the pull-down resistors  606 ,  607  and the differential signal lines  603 ,  604  are disconnected ; while the originally disconnected pull-up resistors  608 ,  609  are connected to the differential signal lines  603 ,  604 , respectively.  
           [0037]    Refer to FIG. 4 b,  the connection between a Devicehost device  60  including a Current-Detection Mode connection-detection circuitry  600  and a USB device  30  is shown in the figure. As described above, a pull-up resistor  308  is connected to a differential signal line  303  which is used to connect to the D+ differential line  403  if the USB device  30  is a High-Speed USB device. On the other hand, a pull-up resistor  309  is connected to a differential signal line  304  which is used to connect to the differential line  404  of the USB cable  40  if the USB device  30  is a Low-Speed device. Assume that the connected device  30  is a High-Speed USB device, the resistance of the pull-up resistor  308  is R H  and the voltage source added to the pull-up resistor  308  is V H , then the current Ip transmitting through the pull-down resistor  606  can be expressed by equation (2): 
             I   p =( V   H   +I×R   H )/( R   H   +R   p )  equation (2) 
           [0038]    On the other hand, assume that the connected device  30  is a Low-Speed USB device, the resistance of the pull-up resistor  309  is R L  and the voltage source added to the pull-up resistor  309  is V L , then the current Im transmitting through the pull-down resistor  607  can be expressed by equation (3): 
             I   m =( V   L   +I×R   L )/( R   L   +R   p )  equation (3) 
           [0039]    By measuring the currents Ip, Im transmitting through the pull-down resistors  606 , 607 , the connected device can be recognized as a USB device (High-Speed or Low-Speed, respectively) by the Devicehost device  60 . The Devicehost device  60  is then switched into “Host-Mode” automatically. Under Host-Mode, the pull-up resistors  608  and  609  of the connection-detection circuitry  600  are remained in a disconnection state.  
           [0040]    Therefore, the Devicehost device  60  is able to identify the type of the device to which it is connected as a USB host or a USB device automatically by utilizing the Current-Detection Mode connection-detection circuitry  600 .  
         Voltage Detection Mode  
         [0041]    Similar to Current-Detection Mode described above, it is unnecessary for the user to switch the mode of the Devicehost device under “Voltage-Detection Mode”. The difference between the two is that a voltage-change rather than a current-change is detected by a voltage-detection circuit to identify the device type of the connected device under Voltage-Detection Mode.  
           [0042]    Refer to FIG. 5 a  and  5   b,  a connection-detection circuitry  700  of the third embodiment according to the invention is shown in the figures. The connection-detection circuitry  700  of Voltage-Detection Mode includes a pair of differential signal lines  703 ,  704 , a power line  711 , a ground line  712 , a pair of pull-down resistors  706  and  707 , a pair of pull-up resistors  708  and  709 , a pair of up-stream resistors  701  and  702 , a power supply system  710 , and a voltage-detection circuit  720 . Wherein, the differential signal lines  703  and  704  are used to connect to the D+ and D− differential signal lines  403  and  404  of the USB cable  40 , respectively. Each of the pull-down resistor  706 , the pull-up resistor  708  and the up-stream resistor  701  is connected to the differential signal line  703  with a switching element, individually. Meanwhile, each of the pull-down resistor  707 , the pull-up resistor  709 , and the up-stream resistor  702  is connected to the differential signal line  704  with a switching element, respectively. Furthermore, a timer  721  is constructed in the voltage-detection circuit  720  and will be explained in details later.  
           [0043]    Instead of a current source, a voltage source V is added to the pair of up-stream resistors  701 ,  702  which are connected to the differential signal lines  703 ,  704  of the connection-detection circuitry  700 . Thus, before any connection taking place, assume that the resistance of the up-stream resistors  701 ,  702  is Rs and the resistance of the pull-down resistors is Rp, then the voltage level Vs of the differential signal lines  703 ,  704  detected by the voltage-detection circuit  720  can be expressed by equation (4): 
             Vs=V×Rp/ ( Rp+Rs )  equation (4) 
           [0044]    Refer to FIG. 5 a,  the connection between a Devicehost device  70  including a Voltage-Detection Mode connection-detection circuitry  700  and a USB host  20  (or a USB hub device) is shown in the figure. As described above, a pair of pull-down resistors  206 ,  207  are connected to the differential signal lines  203 ,  204  inside the USB host  20 . The differential signal lines  203 ,  204  are used to connect to the differential signal lines  403 ,  404  of the USB cable  40 . When the Device host  70  is connected to the USB host  20 , assume that the resistance of the pull-down resistors  206 ,  207  is Rpd, then the voltage level Vh of the differential signal lines  703 ,  704  detected by the voltage detection circuitry can be expressed by equation (5): 
             Vh=V× ( Rpd×Rp )/( Rpd×Rp+Rpd×Rs+Rp×Rs )  (5) 
           [0045]    By comparing the difference of the voltage levels Vs and Vh, the connected device  20  can be recognized as a USB host by the Devicehost device  70 . The Devicehost device  70  is then switched into “Device-Mode” automatically. Under Device-Mode, the connection between the pull-down resistors  706 ,  707  and the differential signal lines  703 ,  704  are disconnected; while the originally disconnected pull-up resistors  708 ,  709  are connected to the differential signal lines  703 ,  704 , respectively.  
           [0046]    Refer to FIG. 5 b,  the connection between a Devicehost device  70  including a Voltage-Detection Mode connection-detection circuitry  700  and a USB device  30  is shown in the figure. When the Devicehost device  70  is connected to a High-Speed USB device  30 , assume that the resistance of the pull-up resistor  308  of the device is R H  and the voltage source added to the pull-up resistor  308  is V H , then the voltage level Vd of the differential line  703  detected by the voltage-detection circuit  720  can be expressed by equation (6): 
             V   d =( V ×( R   p   ×R   H )/( R   p   ×R   H   +R   p   ×R   s   +R   H   ×R   s ))+( V   H ×( R   p   ×R   s )/( R   p   ×R   s   +R   p   ×R   H   +R   S   ×R   H ))  (6) 
           [0047]    On the other hand, if the connected device is a Low-Speed USB device, assume that the resistance of the pull-up resistor  309  is R L  and the voltage source added to the pull-up resistor  309  is V L , then the voltage level V e  of the differential signal line  704  detected by the voltage-detection circuit  720  can be expressed by equation (7): 
             V   e =( V ×( R   p   ×R   L )/( R   p   ×R   L   +R   p   ×R   s   +R   L   ×R   s )) +( V   L ×( R   p   ×R   s )/( R   p   ×R   s   +R   p   ×R   L   +R   s   ×R   L ))  (7) 
           [0048]    By comparing the difference of the voltage levels Vs and Vd or Ve, the connected device  30  can be recognized as a USB device by the Devicehost device  70 . The Devicehost device  70  is then switched into “Host-Mode” automatically. Under Host-Mode, the pull-up resistors  708  and  709  of the connection-detection circuitry  700  are remained in a disconnection state.  
           [0049]    Summing up the above, the three types of connection-detection circuitry are designed to solve the problems existed in the conventional USB devices that the connection and data transmission are forbidden between the USB devices. A “Devicehost” device including the connection-detection circuitry is proposed by the invention. The Devicehost device is able to switch into “Device-Mode” or “Host-Mode” in response to the type of connected device by means of “Manual-Switch Mode”, “Current-detection Mode” or “Voltage-detection Mode”. Under “Manual-Switch Mode”, it is feasible for two Devicehost devices to determine the “HostDevice” relationship and connect to each other by the manual-switch method. However, there are problems in the connection between the Devicehost devices whose “Current-detection Mode” or “Voltage-detection Mode”. Therefore, a set of logic circuit is established in these Devicehost devices to solve the problem. In cooperate with FIG. 6, the set of logic circuit is explained in detail utilizing a Devicehost device of Current-Detection Mode.  
           [0050]    Refer to FIG. 6, the procedure of a Devicehost device of Current-detection Mode to detect the type of the connected device is illustrated in a flow chart.  
           [0051]    First of all, when the Devicehost device is connected to a device (Step  601 ), as described before, a current change of the D+ or D− differential signal line is detected by the current-detection circuit constructed inside the Devicehost (Step  602 ). If the detected current changes from “1” to the value expressed by equation (2) or (3) then the Devicehost device is able to identify that the connected device is a High-Speed USB device or a Low-Speed USB device and switch into “Host-Mode” automatically (Step  603 ).  
           [0052]    However, the detected current is in consist with the current value expressed by equation (1) when a USB host or another devicehost device is connected to the Devicehost device because either of the USB host or the devicehost device is also equipped with a pair of pull-down resistors and a power supply system which can supply a 5V voltage source. Thus, when this phenomenon is detected, the Devicehost device firstly disconnects its internal power supply system which provides the 5V voltage source, and disconnects the connection between the pull-down resistors and the differential signal lines of the connection-detection circuitry (Step  604 ).  
           [0053]    After this, a timer provided within the Devicehost device is activated and a time period is randomly set by the timer (Step  605 ). Every time when the timer is activated, a counting down process is started with the set time period. If the Devicehost device receives a 5V voltage from the connected device during this time period (Step  606 ), then the Devicehost device is able to identify that the connected device is a USB host and switch into “Device-Mode” automatically (Step  607 ).  
           [0054]    On the other hand, if the Devicehost device does not receive a 5V voltage when the counting down process is terminated, that is, the set time period is exceeded, then the power supply system of the Devicehost device is reactivated and the pull-down resistors are connected to the differential signal lines again (Step  608 ). After this, as illustrated in the flow chart, the Connection-detection circuitry of the Devicehost device restarts the current-detection process from Step  602  and the above process is repeated (Step  609 ).  
           [0055]    When the above detection process is proceeded within two Devicehost devices which are connected to each other, it is the “time difference” between the time periods set by the timers of the devices that determines the “Host-device” relationship. That is, when one Devicehost device has reactivated its power supply system and reconnected the pull-down resistors to the differential signal lines; while the other Devicehost device has not yet proceed to the re-connection step, the former one is recognized as a USB host and switches into “Host-Mode” (Step  602  to Step  603 ) and the later one is recognized as a USB device and switches into “Device-Mode” (Step  606  to Step  607 ).  
           [0056]    Therefore, by the above process, the Devicehost device of the invention can accurately identify the type of the connected device and switch into “Device-Mode” or “Host-Mode” automatically in response to the connected device and to proceed the data transmission process.  
           [0057]    While there have been shown and described what are at present considered the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0058]    [0058]FIG. 1 is a schematic diagram which illustrates the connection method of a USB system.  
         [0059]    [0059]FIG. 2 is a schematic diagram of a conventional USB Connection-Detection Circuitry.  
         [0060]    [0060]FIG. 3 is a schematic diagram of a Connection-detection circuitry of the first embodiment according to the present invention.  
         [0061]    [0061]FIG. 4 a  is a schematic diagram illustrating the connection between a device containing a Connection-detection circuitry of the second embodiment according to the present invention and a USB host/hub device.  
         [0062]    [0062]FIG. 4 b  is a schematic diagram illustrating the connection between a device containing a Connection-detection circuitry of the second embodiment according to the present invention and a USB device.  
         [0063]    [0063]FIG. 5 a  is a schematic diagram illustrating the connection between a device containing a Connection-detection circuitry of the third embodiment according to the present invention and a USB host/hub device.  
         [0064]    [0064]FIG. 5 b  is a schematic diagram illustrating the connection between a device containing a Connection-detection circuitry of the second embodiment according to the present invention and a USB device.  
         [0065]    [0065]FIG. 6 is a flow chart illustrating the detection steps of the connection-detection circuitry of the second embodiment according to the present invention. 
     
    
     NOTATION OF THE DRAWINGS  
       [0066]    [0066] 10  USB host  
         [0067]    [0067] 11  root hub  
         [0068]    [0068] 12  connection port  
         [0069]    [0069] 13  connection port  
         [0070]    [0070] 14  USB hub  
         [0071]    [0071] 15  USB function device  
         [0072]    [0072] 16  USB hub  
         [0073]    [0073] 17  USB function device  
         [0074]    [0074] 20  USB host/hub device  
         [0075]    [0075] 200  Up Stream Detection Circuitry  
         [0076]    [0076] 203  differential signal line  
         [0077]    [0077] 204  differential signal line  
         [0078]    [0078] 205  USB transceiver  
         [0079]    [0079] 206  pull-down resistor  
         [0080]    [0080] 207  pull-down resistor  
         [0081]    [0081] 220  voltage detector  
         [0082]    [0082] 30  USB device  
         [0083]    [0083] 300  down stream detection circuitry  
         [0084]    [0084] 303  differential signal line  
         [0085]    [0085] 304  differential signal line  
         [0086]    [0086] 305  USB transceiver  
         [0087]    [0087] 308  pull-up resistor  
         [0088]    [0088] 309  pull-up resistor  
         [0089]    [0089] 40  USB cable  
         [0090]    [0090] 401  VCC power line  
         [0091]    [0091] 402  GND power line  
         [0092]    [0092] 403  d+ differential signal line  
         [0093]    [0093] 404  d− differential signal line  
         [0094]    [0094] 50  USB devicehost  
         [0095]    [0095] 503  differential signal line  
         [0096]    [0096] 504  differential signal line  
         [0097]    [0097] 505  USB transceiver  
         [0098]    [0098] 506  pull-down resistor  
         [0099]    [0099] 507  pull-down resistor  
         [0100]    [0100] 508  pull-up resistor  
         [0101]    [0101] 509  pull-up resistor  
         [0102]    [0102] 510  power supply system  
         [0103]    [0103] 511  manual-switch elements  
         [0104]    [0104] 60  USB devicehost  
         [0105]    [0105] 600  connection-detection circuitry  
         [0106]    [0106] 603  differential signal line  
         [0107]    [0107] 604  differential signal line  
         [0108]    [0108] 605  USB transceiver  
         [0109]    [0109] 606  pull-down resistor  
         [0110]    [0110] 607  pull-down resistor  
         [0111]    [0111] 608  pull-up resistor  
         [0112]    [0112] 609  pull-up resistor  
         [0113]    [0113] 610  power supply system  
         [0114]    [0114] 611  power line  
         [0115]    [0115] 612  ground line  
         [0116]    [0116] 620  current-detection circuit  
         [0117]    [0117] 621  timer  
         [0118]    [0118] 70  USB devicehost  
         [0119]    [0119] 700  connection-detection circuitry  
         [0120]    [0120] 701  up-stream resistor  
         [0121]    [0121] 702  up-stream resistor  
         [0122]    [0122] 703  differential signal line  
         [0123]    [0123] 704  differential signal line  
         [0124]    [0124] 705  USB transceiver  
         [0125]    [0125] 706  pull-down resistor  
         [0126]    [0126] 707  pull-down resistor  
         [0127]    [0127] 710  power supply system  
         [0128]    [0128] 711  power line  
         [0129]    [0129] 712  ground line  
         [0130]    [0130] 720  voltage-detection circuit  
         [0131]    [0131] 721  timer