Abstract:
A switching device for RS-232 serial port and USB serial port is adapted to simultaneously provide a RS-232 serial port and a USB serial port for a micro-processor with a single USART. The switching device can automatically switch to select either of the RS-232 serial port or the USB serial port as a main interface for communicating with other external computer facilities and related peripheries. When one of the serial ports is selected as the main communication interface to communicate with one of external computers, the other one serial port thereof still can transmit signals from the micro-processor to another computer through its transmitting data pin (TXD).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a switching device for selecting RS-232 serial port and USB serial port. More particularly, the present invention relates to using a photo-coupler to automatically select one receiving data pin (RXD line) of both RS-232 serial port and USB serial port so that a computer and peripherals thereof are able to communicate with the RS-232 serial port or the USB serial port. In operation, when one of the RS-232 serial port and the USB serial port is selected, a transmitting data pin (TXD line) of the other is still able to transmit data from a microprocessor to another computer. 
     2. Description of the Related Art 
     Conventionally, a computer usually possesses a single RS-232 (Recommended standard 232) communication port or USB (Universal Serial Bus) communication port and hardly possesses these two ports at the same time. This results in inconvenience in data communication. 
     The conventional communication device using the RS-232 communication port, as shown in  FIG. 1 , includes a single USART (Universal Synchronous Asynchronous Receiver Transmitter) microprocessor  11 , a RS-232/USART converter element  12  and a RS-232 serial port  13 . The communication device  1  adopts serial communication and has a signal transmission line for transmitting and receiving data. The microprocessor  11  contains a single USART set electrically connecting to the RS-232/USART converter element  12  for converting voltage signals. Further, the RS-232/USART converter element  12  electrically connects to the RS-232 serial port  13  that communicates with a first computer  2  via a transmission line. The first computer  2  is able to transmit and receive data bit by bit through a transmission line. 
     In 1969 the Electrical Industries Association adopted the RS-232 communication protocol which has two voltage signal ranges: one ranging between −3V and −25V denoting logical signal “1” and the other ranging between 3V and 25V denoting logical signal “0”. A computer peripheral, such as UPS, contains a microprocessor control unit (MCU) using a voltage 5V or 3.3V. Therefore, the conventional communication device  1  must include the RS-232/USART converter element  12  for converting transmission signals of the microprocessor  11  and the RS-232 serial port  13 . 
     Referring to  FIG. 2 , the other conventional communication device  10  includes a single USART microprocessor  11 , a USB/USART converter element  14  and a USB serial port  15 . The microprocessor  11  contains a single USART set electrically connecting to the USB/USART converter element  14  for converting voltage signals. Further, the USB/USART converter element  14  electrically connects to the USB serial port  15  that communicates with a second computer  20  via a transmission line. The second computer  20  is able to transmit and receive data bit by bit through a transmission line. 
     The USB communication protocol was developed by Intel, Compaq, DEC, IBM, Microsoft, NEC, and Northern Telecom. However, USB protocol has replaced RS-232 protocol and become a single, general-purpose port for computer peripherals. It is apparent that the USB serial port is a universal protocol port for computer peripherals communicating with a host computer. 
     Recently, communication interfaces of both RS-232 and USB are widely applied to a computer system and peripherals. The peripheries of the computer must offer these two interfaces at the same time. So far, the RS-232 serial port of a computer peripheral is only available for an RS-232 protocol interface of the computer system. To exchange the RS-232 protocol interface of the computer system with a USB interface, it is necessary to add an RS-232/USB converter. Alternatively, the USB serial port of a computer peripheral is only available for a USB interface of the computer system. To exchange the USB interface of the computer system with an RS-232 protocol interface, it is necessary to add a USB/RS-232 converter. From the viewpoint of manufacture, it is inconvenient for production management to produce the different peripheries with only one of communication interfaces for RS-232 and USB. 
     To solve this problem, a computer peripheral adopting a communication device  3  having both of a RS-232 serial port and a USB serial port are shown in  FIGS. 3 and 4 . 
       FIG. 3  depicts a schematic view of dual communication interfaces of a communication device for RS-232 and USB. The communication device  3  includes a dual USARTs microprocessor  31 , a RS-232/USART converter element  32 , a RS-232 serial port  33 , a USB/USART converter element  34  and a USB serial port  35 . One USART interface of the double USART microprocessor  31  electrically connects to the RS-232/USART converter element  32 . And, the RS-232/USART converter element  32  electrically connects to the RS-232 serial port  33  for providing a RS-232 protocol interface. Subsequently, the RS-232 serial port  33  communicates with a first computer  2 . The other USART interface of the dual USARTs microprocessor  31  electrically connects to the USB/USART converter element  34 . And, the USB/USART converter element  34  electrically connects to the USB serial port  35  for providing a USB interface. Subsequently, the USB serial port  35  communicates with a second computer  20 . 
       FIG. 4  depicts a schematic view of other dual communication interfaces of a communication device for RS-232 and USB. The communication device  4  includes a first single USART microprocessor  41 , a second single USART microprocessor  41 ′, a RS-232/USART converter element  42 , a RS-232 serial port  43 , a USB/USART converter element  44  and a USB serial port  45 . A USART interface of the first USART microprocessor  41  electrically connects to the RS-232/USART converter element  42 . And, the RS-232/USART converter element  42  electrically connects to the RS-232 serial port  43  for providing a RS-232 protocol interface. Subsequently, the RS-232 serial port  43  communicates with a first computer  2 . A USART interface of the second USART microprocessor  41 ′ electrically connects to the USB/USART converter element  44 . And, the USB/USART converter element  44  electrically connects to the USB serial port  45  for providing a USB interface. Subsequently, the USB serial port  45  communicates with a second computer  20 . 
     However, the communication device including RS-232 and USB may increase manufacture cost even though it has an advantage of providing dual communication functions for RS-232 and USB simultaneously. 
     The present invention intends to provide a switching device for RS-232 serial port and USB serial port using a photo-coupler device to automatically select one receiving data pin (RXDA and RXDB lines) of the RS-232 serial port or the USB serial port for communicating data. Firstly, a microprocessor with only one USART can be used to perform automatically selecting one receiving data pin (RXD line) of both RS-232 serial port and USB serial port as a main COM port for communicating data from the microprocessor to a first computer. Secondly, the other unselected one of a transmitting data pin (TXD line) of the RS-232 serial port and the USB serial port that is regarded as a secondary COM port still also transmits data from the microprocessor to a second computer. Thereby, the switching device for RS-232 serial port and USB serial port employs the photo-coupler device to automatically select one of the RS-232 serial port or the USB serial port in such a way to mitigate and overcome the above problem. 
     SUMMARY OF THE INVENTION 
     The primary objective of this invention is to provide a switching device of a single USART microprocessor using a photo-coupler device to automatically select RS-232 serial port or USB serial port. In operation, the selected one of the RS-232 serial port or the USB serial port is regarded as a main COM port while the other unselected one of transmitting data pins (TXD lines) of the RS-232 serial port and the USB serial port communicates data from the microprocessor to another computer. Thereby, it is convenient in operation and can reduce the manufacture cost. 
     The switching device for RS-232 serial port and USB serial port in accordance with the present invention includes a single USART microprocessor, a photo-coupler device, a RS-232/USART converter element, a RS-232 serial port, a USB/USART converter element and a USB serial port. The single USART microprocessor has a transmitting data pin (TXD line) and a receiving data pin (RXD line). The transmitting data pin of the single USART microprocessor connects to a transmitting data pin (TXDA) of the RS-232/USART converter element and a transmitting data pin (TXDB) of the USB/USART converter element together. The receiving data pin of the single USART microprocessor connects to two anodes of two diodes, and two cathodes of the two diodes connects to a receiving data pin (RXDA) of the RS-232/USART converter element and a receiving data pin (RXDB) of the USB/USART converter element. 
     A separate aspect of the present invention is that a first terminal of the photo-coupler device acts as the control input and is controlled by +5V supplied from a power source of the USB serial port through a current-limiting resistor. And a second terminal of the photo-coupler device connects to the receiving data pin (RXDA) of the RS-232/USART converter element. In this aspect, the USB serial port has a high priority for communication with one of the computers. 
     A further separate aspect of the present invention is that a DTR pin of the RS-232 serial port controls a first terminal of the photo-coupler device. And a second terminal of the photo-coupler device connects to the receiving data pin (RXDB) of the USB/USART converter element. In this aspect, the RS-232 serial port has a high priority for communication with one of computers. 
     In a yet further separate aspect of the present invention, a DIP switch is used to select one of the RS-232 serial port and the USB serial port. In operation, the selected one of the RS-232 serial port and the USB serial port has a high priority for communication with one of computers. 
     In a yet further separate aspect of the present invention, a first terminal of the photo-coupler device acts as a control input and is controlled by control signals supplied from the USB serial port through the USB/USART converter element and the current-limiting resistor. And a second terminal of the photo-coupler device connects to the receiving data pin (RXDA) of the RS-232/USART converter element. 
     Thereby, the switching device selects one of the RS-232 serial port and the USB serial port regarded as a main COM port while the unselected other one of the RS-232 serial port and the USB serial port can still transmit data from the microprocessor to another computer 
     Other objectives, advantages and novel features of the invention will become more apparent from the following detailed description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will now be described in detail with reference to the accompanying drawings wherein: 
         FIG. 1  is a schematic view of a conventional communication device having a RS-232 serial port in accordance with the prior art; 
         FIG. 2  is a schematic view of another conventional communication device having a USB serial port in accordance with the prior art; 
         FIG. 3  is a schematic view of a conventional communication device having both of a RS-232 serial port and a USB serial port in accordance with the prior art; 
         FIG. 4  is a schematic view of another conventional communication device having both of a RS-232 serial port and a USB serial port in accordance with the prior art; 
         FIG. 5  is a schematic view of a switching device for RS-232 serial port and USB serial port in accordance with a first embodiment of the present invention; 
         FIG. 6  is a schematic view of a switching device for RS-232 serial port and USB serial port in accordance with a second embodiment of the present invention; 
         FIG. 7  is a schematic view of a switching device for RS-232 serial port and USB serial port in accordance with a third embodiment of the present invention; and 
         FIG. 8  is a schematic view of a switching device for RS-232 serial port and USB serial port in accordance with a fourth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 5 , it depicts a schematic view of a switching device for RS-232 serial port and USB serial port in accordance with a first embodiment of the present invention. In this embodiment, the switching device  5  includes a single USART microprocessor  51 , a photo-coupler device  52 , a RS-232/USART converter element  53 , a RS-232 serial port  54 , a USB/USART converter element  55 , a USB serial port  56 , a first diode  57 , a second diode  57 ′ and a current-limiting resistor  58 . 
     Still referring to  FIG. 5 , the single USART microprocessor  51  has a transmitting data pin (TXD) connecting to a transmitting data pin (TXDA) of the RS-232/USART converter element  53  and a transmitting data pin (TXDB) of the USB/USART converter element  55 . Correspondingly, the single USART microprocessor  51  has a receiving data pin (RXD) connecting to two cathodes of the first diode  57  and the second diode  57 ′. Two anodes of the first diode  57  and the second diode  57 ′ connect with a receiving data pin (RXDA) of the RS-232/USART converter element  53  and a receiving data pin (RXDB) of the USB/USART converter element  55 . A first terminal of the photo-coupler device  52  acts as the control input and is controlled by +5V supplied from a power source of the USB serial port  56  through the current-limiting resistor  58 . And a second terminal of the photo-coupler device  52  connects to the receiving data pin (RXDA) of the RS-232/USART converter element  53 . 
     Further, the RS-232 serial port  54  connects to the RS-232/USART converter element  53  while the USB serial port  56  connects to the USB/USART converter element  55   
     Still referring to  FIG. 5 , in operation, the RS-232 serial port  54  continuously communicates with the single USART microprocessor  51  through the RS-232/USART converter element  53  for a first computer  2 . Once a second computer  20  hooks up the USB serial port  56 , the first terminal of the photo-coupler device  52  is actuated and the second terminal conducts to cause the receiving data pin (RXDA) of the RS-232/USART converter element  53  is disabled. This permits changing the single USART microprocessor  51  to communicate data to the second computer  20  through the USB serial port  56 . Until the second computer  20  is removed from the USB serial port  56 , the second terminal of the photo-coupler device  52  is opened so that the receiving data pin (RXDA) of the RS-232/USART converter element  53  is enabled again. Namely, the single USART microprocessor  51  returns to communicate with the first computer  2  through the RS-232 serial port  54 . The switching device  5  uses the photo-coupler device  52  for selecting one of the RS-232 serial port  54  and the USB serial port  56 . In this embodiment, the USB serial port  56  has the high priority for communication with a computer. 
     Turning now to  FIG. 6 , it depicts a schematic view of a switching device for RS-232 serial port and USB serial port in accordance with a second embodiment of the present invention. In this embodiment, the switching device  6  includes a single USART microprocessor  61 , a photo-coupler device  62 , a RS-232/USART converter element  63 , a RS-232 serial port  64 , a USB/USART converter element  65 , a USB serial port  66 , a first diode  67 , a second diode  67 ′ and a current-limiting resistor  68 . 
     Still referring to  FIG. 6 , the single USART microprocessor  61  has a transmitting data pin (TXD) connecting to a transmitting data pin (TXDA) of the RS-232/USART converter element  63  and a transmitting data pin (TXDB) of the USB/USART converter element  65 . Correspondingly, the single USART microprocessor  51  has a receiving data pin (RXD) connecting to two cathodes of the first diode  67  and the second diode  67 ′. Two anodes of the first diode  67  and the second diode  67 ′ connect with a receiving data pin (RXDA) of the RS-232/USART converter element  63  and a receiving data pin (RXDB) of the USB/USART converter element  65 . A DTR pin of the RS-232 serial port  64  controls a first terminal of the photo-coupler device  62 . And a second terminal of the photo-coupler device  62  connects to the receiving data pin (RXDB) of the USB/USART converter element  65 . 
     Further, the RS-232 serial port  64  connects to the RS-232/USART converter element  63  while the USB serial port  66  connects to the USB/USART converter element  65 . 
     Still referring to  FIG. 6 , in operation, the USB serial port  66  continuously communicates with the single USART microprocessor  61  through the USB/USART converter element  65  for a second computer  20 . Once a first computer  2  hooks up the RS-232 serial port  64 , the first terminal of the photo-coupler device  62  is actuated and the second terminal is conducted that the receiving data pin (RXDA) of the USB/USART converter element  63  is disabled. This permits changing the single USART microprocessor  61  to communicate data to the first computer  2  through the RS-232 serial port  64 . Until the first computer  2  is removed from the RS-232 serial port  64 , the second terminal photo-coupler device  62  is opened that the receiving data pin (RXDA) of the USB/USART converter element  63  is enable again. Namely, the single USART microprocessor  51  returns to communicate with the second computer  20  through the USB serial port  66 . The switching device  6  uses the photo-coupler device  62  for selecting one of the RS-232 serial port  64  and the USB serial port  66 . In this embodiment, the RS-232 serial port  64  has the high priority for communication with a computer. 
     Referring to  FIG. 7 , it depicts a schematic view of a switching device for RS-232 serial port and USB serial port in accordance with a third embodiment of the present invention. In this embodiment, the switching device  7  includes a single USART microprocessor  71 , a first photo-coupler device  72 , a second photo-coupler device  72 ′, a RS-232/USART converter element  73 , a RS-232 serial port  74 , a USB/USART converter element  75 , a USB serial port  76 , a first diode  77 , a second diode  77 ′, a first current-limiting resistor  78 , a second current-limiting resistor  79  and a DIP switch  70 . 
     Still referring to  FIG. 7 , in this embodiment, the DIP switch  70  is used to select one of the RS-232 serial port  74  and the USB serial port  76  in manual operation. In operation, the selected one of the RS-232 serial port  74  and the USB serial port  76  has the high priority for communication with one of computers  2  and  20 . 
     Referring to  FIG. 8 , it depicts a schematic view of a switching device for RS-232 serial port and USB serial port in accordance with a fourth embodiment of the present invention. In this embodiment, the switching device  8  includes a single USART microprocessor  81 , a photo-coupler device  82 , a RS-232/USART converter element  83 , a RS-232 serial port  84 , a USB/USART converter element  85 , a USB serial port  86 , a first diode  87 , a second diode  87 ′ and a current-limiting resistor  88 . 
     Still referring to  FIG. 8 , the single USART microprocessor  81  has a transmitting data pin (TXD) connecting to a transmitting data pin (TXDA) of the RS-232/USART converter element  83  and a transmitting data pin (TXDB) of the USB/USART converter element  85 . Correspondingly, the single USART microprocessor  81  has a receiving data pin (RXD) connecting to two cathodes of the first diode  87  and the second diode  87 ′. Two anodes of the first diode  87  and the second diode  87 ′ connect with a receiving data pin (RXDA) of the RS-232/USART converter element  83  and a receiving data pin (RXDB) of the USB/USART converter element  85 . A first terminal of the photo-coupler device  82  acts as the control input and is controlled by control signals supplied from the USB serial port  86  through the USB/USART converter element  85  and the current-limiting resistor  88 . And a second terminal of the photo-coupler device  82  connects to the receiving data pin (RXDA) of the RS-232/USART converter element  83 . 
     Further, the RS-232 serial port  84  connects to the RS-232/USART converter element  83  while the USB serial port  86  connects to the USB/USART converter element  85 . 
     Still referring to  FIG. 8 , in operation, the RS-232 serial port  84  continuously communicates with the single USART microprocessor  81  through the RS-232/USART converter element  83  for a first computer  2 . Second computer  20  hooks up the USB serial port  86  for communication. When the USB/USART converter element  85  received a complete command from the second computer  20 , a control signal from the USB/USART converter element  85  actuates the first terminal of the photo-coupler device  82  and then the second terminal is closed. Accordingly, the receiving data pin (RXDA) of the RS-232/USART converter element  83  is disabled. This permits changing the single USART microprocessor  81  to communicating data to the second computer  20  through the USB serial port  86 . Until another complete command from the second computer  20  is sent to the single USART microprocessor  81 , the first terminal of the photo-coupler device  82  is cut off. Accordingly, the second terminal photo-coupler device  82  is opened so that the receiving data pin (RXDA) of the RS-232/USART converter element  83  is enabled again. Namely, the single USART microprocessor  81  returns to communicate with the first computer  2  through the RS-232 serial port  84 . The switching device  8  uses the photo-coupler device  82  for selecting one of the RS-232 serial port  84  and the USB serial port  86 . 
     Referring back to  FIG. 3 , the conventional communication device  3  must employ a dual USARTs microprocessor  31  that will increase manufacture cost. Similarly, referring back to  FIG. 4 , the conventional communication device  4  must employ two single USART microprocessors  41  and  41 ′ that may also increase manufacture cost. 
     Referring again to the  FIG. 5 to 8 , each of the switching devices employs only a single USART microprocessor and a photo-coupler device that may reduce manufacture cost. Also, each of the switching devices  5  to  8  provides with the RS-232 serial port and the USB serial port at the same time. It is an advantage of using the photo-coupler device that the selected one of the RS-232 serial port and the USB serial port is regarded as a main COM port while the unselected other one of the RS-232 serial port and the USB serial port transmitting data from the microprocessor to another computer. 
     Although the invention has been described in detail with reference to its presently preferred embodiment, it will be understood by one of ordinary skill in the art that various modifications can be made without departing from the spirit and the scope of the invention, as set forth in the appended claims.