Abstract:
A data control cable connecting between a mobile device and a host device for establishing data communication between the mobile device and the host device. The cable contains a clock generator, which generates a data control signal used for controlling and limiting when the host device can send data to the mobile device. When the data control signal is output to the host device, the host device is permitted to transmit data to the mobile device.

Description:
BACKGROUND OF INVENTION 
   1. Field of the Invention 
   The present invention relates to cable for connecting a mobile device to a host device, and more specifically, to a cable for controlling a data transmission rate between a mobile device and a host device. 
   2. Description of the Prior Art 
   Since modern day mobile devices such as cellular phones have General Packet Radio Service (GPRS) capabilities, mobile devices can be used to connect host devices, such as notebook computers, to the Internet. The mobile device can communicate with the host device through a data bus interface that is similar to the method in which a computer communicates with a modem. 
   Please refer to FIG.  1 .  FIG. 1  is a block diagram of a host device  10  communicating with a modem  14  according to the prior art. The host device  10  and the modem  14  send and receive data signals  16 ,  18  and control signals  20 ,  22  for exchanging information between the host device  10  and the modem  14 . Data signal  16  is sent from the host device  10  as transmitted data (Tx) and received by the modem  14  as received data (Rx). Similarly, data signal  18  is sent from the modem  14  as Tx and received by the host device  10  as Rx. Data signals  16 ,  18  each transmit serial data at a predetermined baud rate. The baud rate is defined as the transmission rate of one bit of data in each byte, the byte containing eight data bits, a start bit, and a stop bit. 
   Control signal  20  is sent from the modem  14  as a clear to send (CTS) signal and received by the host device  10  as a request to send (RTS) signal. Likewise, control signal  22  is sent from the host device  10  as a CTS signal and received by the modem  14  as an RTS signal. When the host device  10  sends the CTS signal  22  with a value of “1” to the modem  14 , this indicates that the host device  10  can accept data received from the modem  14  on data signal  18 . On the other hand, when the host device  10  sends the CTS signal  22  with a value of “0” to the modem  14 , this indicates that the host device  10  cannot currently accept data received from the modem  14  on data signal  18 . Instead, the modem  14  should wait until the host device  10  issues the CTS signal  22  with a value of “1” before sending data to the host device  10  on data signal  18 . Since communication between the host device  10  and the modem  14  is bi-directional, data control signals  20  and  22  serve the same purpose. Therefore, the modem  14  is also able to issue the CTS signal  20  to the host device  10  for controlling the flow of data on the data signal  16  from the host device  10  to the modem  14 . 
   Please refer to FIG.  2 .  FIG. 2  is a diagram of a host device  30  which can communicate with a mobile device  42  according to the prior art. The host device  30  communicates with the mobile device  42  through a cable  36 . The cable  36  has a serial connector  38  that plugs into a corresponding serial port  34  on the host device  30 . The cable  36  also has an earphone connector  40  that plugs into a corresponding earphone jack  44  on the mobile device  42 . The serial connector  38  is typically an RS-232 serial connector, although any serial connector can be used instead. Due to limitations of the earphone connector  40 , only two data signals can be transmitted back and forth between the host device  30  and the mobile device  42 . Therefore, unlike the host device  10  and the modem  14 , no control signals can be sent between the host device  30  and the mobile device  42 . 
   Please refer to FIG.  3 .  FIG. 3  is a block diagram of the host device  30  communicating with the mobile device  42  according to the prior art. As mentioned before, only two data signals  46 ,  48  are sent between the host device  30  and the mobile device  42 . Data signal  46  is sent from the host device  30  as Tx and received by the mobile device  42  as Rx. Similarly, data signal  48  is sent from the mobile device  42  as Tx and received by the host device  30  as Rx. Using the cable  36 , bidirectional communication between the host device  30  and the mobile device  42  is possible, but problems may arise due to the lack of control signals CTS and RTS. The host device  30  has higher processing power and speed than the mobile device  42 , therefore, it is possible for the host device  30  to transmit data to the mobile device  42  through the data signal  46  at a higher rate than the mobile device  42  is capable of processing, which can cause problems. 
   Please refer to FIG.  4 A and FIG.  4 B. FIG.  4 A and  FIG. 4B  are timing diagrams illustrating the transmission of data from the host device  30  to the mobile device  42  through data signal  46 . In  FIG. 4A , the host device  30  is transmitting data through data signal  46  at a baud rate of 19,200 bps (bits per second). Since the earphone connector  40  is only capable of transmitting and receiving data signals  46  and  48 , the CTS and RTS signals are not used. Therefore, the RTS signal shown in  FIG. 4A  is shown as having a constant value of “1” throughout the transmission of data signal  46 . Fortunately, at the baud rate of 19,200 bps, the mobile device  42  has no trouble receiving and processing the data sent from the host device  30 . 
   However, in  FIG. 4B , the host device  30  is transmitting data through data signal  46  at a baud rate of 115,200 bps. Again, the RTS signal maintains a constant value of “1” throughout the transmission of data signal  46 . Unfortunately, at this high baud rate, the mobile device  42  is not able to receive and process all of the data transmitted from the host device  30 . Since the control signal RTS is not used to notify the host device  30  that the mobile device  42  is not able to receive data, the mobile device  42  will be overwhelmed, and may even crash. 
   SUMMARY OF INVENTION 
   It is therefore a primary objective of the claimed invention to provide a data control cable connecting to a mobile device and a host device for establishing data communication between the mobile device and the host device in order to solve the above-mentioned problems. 
   According to the claimed invention, a data control cable connects to a mobile device and a host device for establishing data communication between the mobile device and the host device. The data control cable contains a first data input port for receiving a first data sent from the host device, a second data input port for receiving a second data sent from the mobile device, a first data output port for outputting the first data received from the host device to the mobile device, a second data output port for outputting the second data received from the mobile device to the host device, a clock generator for generating a data control signal used to control when the host device is capable of sending the first data, and a control output port for outputting the data control signal generated by the clock generator to the host device. 
   It is an advantage of the claimed invention that the data control cable contains the clock generator for generating the data control signal. The data control signal limits the amount of data that the host device can send to the mobile device, and prevents the mobile device from being overwhelmed with data and crashing. 
   These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment, which is illustrated in the various figures and drawings. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
       FIG. 1  is a block diagram of a host device communicating with a modem according to the prior art. 
       FIG. 2  is a diagram of a host device which can communicate with a mobile device according to the prior art. 
       FIG. 3  is a block diagram of the host device from  FIG. 2  communicating with the mobile device according to the prior art. 
     FIG.  4 A and  FIG. 4B  are timing diagrams illustrating the transmission of data from the host device to the mobile device through a data signal according to the prior art. 
       FIG. 4C  is a timing diagram illustrating the transmission of data from a host device to a mobile device according to the present invention. 
       FIG. 5  is a diagram of a host device which can communicate with a mobile device according to the present invention. 
       FIG. 6  is a block diagram of the host device communicating with the mobile device according to the present invention. 
   

   DETAILED DESCRIPTION 
   Please refer to FIG.  5 .  FIG. 5  is a diagram of a host device  100  which can communicate with a mobile device  130  according to the present invention. For example, the host device  100  may be a computer, and the mobile device  130  may be a cellular phone. The host device  100  communicates with the mobile device  130  through a cable  120 . The cable  120  has a serial connector  122  that plugs into a corresponding serial port  112  on the host device  100 . The cable  120  also has an earphone connector  126  that plugs into a corresponding earphone jack  132  on the mobile device  130 . Unlike the prior art cable  36 , however, the cable  120  of the present invention has a clock generator  124 , which will be explained below. The serial connector  122  is typically an RS-232 serial connector, although any serial connector can be used instead. Because the earphone connector  126  is only able to transmit two data signals between the host device  100  and the mobile device  130 , the present invention cable  120  makes use of the clock generator  124  to provide a control signal. 
   Please refer to FIG.  6 .  FIG. 6  is a block diagram of the host device  100  communicating with the mobile device  130  according to the present invention. As with the prior art, only two data signals  140 ,  142  are sent between the host device  100  and the mobile device  130 . Data signal  140  is sent from the host device  100  as Tx through a first data input port  150  of the cable  120  and received by the mobile device  130  as Rx through a first data output port  160  of the cable  120 . Similarly, data signal  142  is sent from the mobile device  130  as Tx through a second data input port  162  of the cable  120  and received by the host device  100  as Rx through a second data output port  152  of the cable  120 . Unlike the prior art, the clock generator  124  generates a control signal which acts as a CTS signal sent from the mobile device  130  and received by the host device  100  as an RTS signal  146  through a control output port  156  of the cable  120 . A CTS signal  144  is generated by the host device  100  and is input to the cable  120  through a control input port  154 , but is not transmitted by the cable  120  since the cable  120  is not able to transmit additional signals and since the host device  100  typically has much greater data processing ability than the mobile device  130 . 
   The RTS signal  146  generated by the clock generator  124  controls the rate at which the host device  100  is able to send data to the mobile device  130 . A user of the cable  120  is able to set both the frequency and the duty cycle of the RTS signal  146  generated by the clock generator  124  to adjust a data transfer rate. By adjusting the frequency and duty cycle of the RTS signal  146  according to the specifications of the mobile device  130 , optimum data transmission rates can be obtained. 
   Please refer to  FIG. 4C  with reference to FIG.  4 A and FIG.  4 B.  FIG. 4C  is a timing diagram illustrating the transmission of data from the host device  100  to the mobile device  130  according to the present invention. Unlike the prior art cable  36 , which is shown in FIG.  4 A and  FIG. 4B , the RTS signal  146  of the present invention is not held at a value of “1”. Instead, the clock generator  124  generates an oscillating value for the RTS signal  146  that is shown in FIG.  4 C. Therefore, while the value of the RTS signal  146  is “0”, the host device  100  is not able to transmit data to the mobile device  130 . Only when the value of the RTS signal  146  is “1” will the host device  100  be able to send data to the mobile device  130  through the data signal  140 . Since each bit of data is transmitted at the same rate as before, the baud rates shown in FIG.  4 B and  FIG. 4C  are identical. However, the use of the RTS signal  146  forces the host device  100  to wait a longer period of time between transmission of successive bytes of data. Therefore, the use of the RTS signal  146  generated by the clock generator  124  lowers the throughput rate of data sent from the host device  100  to the mobile device  130 , but use of the RTS signal  146  also prevents the mobile device  130  from crashing due to being overwhelmed with data from the host device  100 . 
   Please note that the present invention is not limited to a cable that connects a cellular phone to a computer. The cable can also be used to connect any host device to a mobile device for allowing the host device to transmit and receive data signals through the mobile device. 
   Compared to the prior art cable  36 , the present invention cable  120  contains the clock generator  124  for producing the RTS signal  146 . The use of the RTS signal  146  prevents the host device  100  from transmitting data to the mobile device  130  at a rate exceeding the maximum rate at which the mobile device  130  can receive and process data. The clock generator  124  prevents the mobile device  130  from crashing, and ultimately improves data transmission from the host device  100  to the mobile device  130 . Since the frequency and duty cycle of the RTS signal  146  can be adjusted, the mobile device  130  is able to receive data at the highest possible rate without crashing the mobile device  130 . 
   Those skilled in the art will readily observe that numerous modifications and alterations of the device may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.