Abstract:
A data transmission system connects a first device and a second devices, and transmits a signal therebetween. The data transmission system includes a first interface for interfacing the first device and the second device, and a second interface for interfacing the first device and the second device. The first device outputs the signal, with the signal having one of a plurality of voltage ranges. A selector selects one of the first interface and the second interface. The data transmission system also includes an indicator for indicating whether the voltage range of the signal output from the first device is out of a predetermined voltage range of the selected one interface, when the selector selects the one interface.

Description:
This application is a continuation, of application Ser. No. 08/433,571, filed May 3, 1995, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a data transmission system having a main device, such as a computer, connected to a plurality of peripheral devices which may transmit different types of signals to the main device. 
     Conventionally, peripheral devices which transmit data to a main computer employ one of more signal transmitting standards. For instance, bar code readers which are connected to a host computer may output a TTL signal or an RS-232C signal. If the bar code reader outputs a TTL signal, then a +5 V signal corresponds to a logical HIGH, and a 0 V signal corresponds to a logical LOW. However, if the bar code reader outputs an RS-232C signal, then a -10 V signal corresponds to a logical HIGH, and a +10 V signal corresponds to a logical LOW. 
     Accordingly, if a peripheral device, such as the bar code reader, which outputs one type of signal is attached to an interface of the host computer which is designed to accept another type of signal, erroneous operation of the data transmission system will occur. Further, since the RS-232C signal has a wider operating voltage range than the TTL signal, if a peripheral device which outputs an RS-232C signal is attached to a TTL interface of the host computer for a certain period of time, damage to the TTL interface may occur. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide an improved data transmission system which indicates to a user of the data transmission system a condition that a device having a predetermined operating voltage range is connected to an interface having an operating voltage range which is narrower than the predetermined operating voltage range. 
     It is another object of the present invention to provide an improved data transmission system in which an indicator indicates an erroneous connection of a device to the interface, as well as information related to data transmitted from the device to the interface. 
     According to an aspect of the present invention, there is provided a data transmission system for connecting a first device with a second device, a signal being exchanged between the first device and the second device. The data transmission system includes: 
     a first interface for interfacing the first device with the second device. The first device outputs the signal which may include one of a plurality of voltage ranges. The data transmission system also includes a second interface for interfacing the first device with the second device, a selector switch for selecting one of the first interface and the second interface, and an indicator for indicating whether the voltage range of the signal received from the first device is out of a predetermined voltage range of the selected one interface, when the selector switch selects the one interface. 
     Optionally, the first device includes a peripheral device and the second device includes a host computer. The host computer receives data from the peripheral device through the data transmission system. 
     Further, the indicator may also be used for indicating an erroneous operating condition of the first device in accordance with the data transmitted from the first device to the second device. 
     Further optionally, the first device may output either, e.g., an RS-232C signal or a TTL signal, with the first and the second interfaces interfacing the TTL and the RS-232C signals, respectively. However, the types of interfaces are not limited to TTL and RS-232C. 
     Optionally, the indicator can be actuated with power only from the received signal if the first interface receives the signal having a voltage which is out of the predetermined voltage range. Therefore, the data transmission system can indicate that the first device is connected to an incorrect interface, even if the second device is not operable. This provides additional protection in the case that the first device is incorrectly connected. 
     Further optionally, the data transmission system further includes a device for receiving an error signal from the second device, the receiving a device driving the indicator when the error signal is received. The receiving device may include a switching circuit, which drives the indicator when the error signal is received. 
     Furthermore, the second device includes a processor for processing the signal transmitted from the first device. The processor outputs the error signal when an error condition is detected during the processing of the signal. 
     Still optionally, the indicator may include, e.g., an LED or other light emitting device which emits light when voltage is applied. Further, the light emitting device may be connected in series to rectifiers so that the light emitting device emits (or does not emit) light depending on the polarity of voltage of the signal transmitted from the first device to the first interface. Furthermore, any other indicator (e.g., visual or aural) may alternatively be used. 
     According to another aspect of the present invention, there is provided a data transmission system for connecting a first device to a second device. The data transmission system includes at least two interfaces selectively connected to the first device for receiving a signal from the first device and an indicator capable of being actuated to indicate an erroneous operating condition of the first device. The erroneous operating condition is included in the signal. When one of the at least two interfaces receives a signal having a voltage range wider than a range to be applied to one of the at least two interfaces, the indicator is actuated. 
     Optionally, when the one of the at least two interfaces receives the signal having a negative voltage value, the indicator is actuated, and when the one of the at least two interfaces receives the signal having a positive voltage value, the indicator is not actuated. 
     wherein when one of the two interfaces receives a signal having voltage range wider than a range to be applied to the one of the two interfaces, the indicator is actuated. 
     Optionally, when the one of the two interfaces receives the signal having a negative voltage value, the indicator is actuated, and 
     wherein when the one of the two interfaces receives the signal having a positive voltage value, the indicator is not actuated. 
     According to a further aspect of the present invention, there is provided a data transmission system for connecting a peripheral device to a host computer. The data transmission device including at least two interfaces for receiving a signal from the peripheral device, each of the interfaces selectable by a switch, and an indicator for indicating information contained within the signal. When the switch selects one of the at least two interfaces, the indicator indicates information related to a voltage of the signal received from the peripheral device. When the switch selects either of the at least two interfaces the indicator also indicates information related to data transmitted by the signal. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a data transmission system embodying the present invention; and 
     FIG. 2 is a schematic diagram of a portion of the data transmission system shown in FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     FIG. 1 is a block diagram of a data transmission system 1, embodying the present invention. 
     Data transmission system 1 includes a host computer having a CPU 100. Data transmission system 1 has a power source 8, and an input terminal 6. A peripheral device (not shown) is attached to the input terminal 6 and connected, via switch 5, to a first interface 3 or a second interface 4. The first interface 3 is provided to communicate with peripheral devices which output a TTL signal, while the second interface 4 is provided to communicate with peripheral devices which output, e.g., e.g., an RS-232C signal. The TTL signal has two values: a +5 V signal which corresponds to a logical HIGH, and a 0 V signal which corresponds to a logical LOW. Similarly, the RS-232C signal has two values: a -10 V signal which corresponds to a logical HIGH, and a +10 V signal which corresponds to a logical LOW. 
     An output of the first interface 3 and an output of the second interface 4 are connected to inputs of an AND gate 2. In the preferred embodiment, the first interface 3 and the second interface 4 are active LOW. Therefore, when one of the interfaces (3,4) is selected, the output of the other interface (3,4) remains HIGH. Thus, the data output by the AND gate 2 will be the same as the data output from the selected interface (3,4), since the other input to the AND gate 2 remains HIGH. The output of the AND gate 2 is then fed to CPU 100. 
     The CPU 100 drives a switching circuit 7 to control an operation of an error indicator 10. When the switching circuit 7 is controlled to turn ON the error indicator 10, current flows from the power source 8 through the switching circuit 7 to the error indicator 10. The current flow is controlled by a current controller 9 and a current controller 13. A voltage across the error indicator 10 is controlled by rectifier 12. 
     Further, rectifier 14 provides proper biasing, such that when a peripheral device which outputs an RS-232C signal inadvertently connected to the first interface 3 by the switch 5, the error indicator 10 is biased to turn ON. The signal output from the peripheral device to the input terminal 6 can be detected, and the error indicator 10 turned ON to indicate an incorrect connection, by using power provided by the signal output from the peripheral device. Thus, the error indicator 10 will be turned ON even if no power is provided from the power source 8. It is therefore not necessary to use the power source 8 in order to indicate a connection of a peripheral device to an incorrect interface. 
     As also described above, the CPU 100 can drive the switching system 7 and thereby control the error indicator 10. Thus, if there is a data error from the peripheral device which is detected by the CPU 100, this error can be indicated. Therefore, according to the preferred embodiment, more than one type of error can be indicated by a single error indicator. 
     FIG. 2 shows a schematic diagram of a portion of the data transmission system 1. As shown in FIG. 2, the switching system 7 comprises transistor 7a, resistor 7b and resistor 7c. The current controller 9 comprises resistor 9a, while the current controller 13 comprises resistor 13a. The error indicator 10 comprises LED 10a, while the rectifiers 12 and 14 comprise diodes 12a and 14a, respectively. 
     An operation of the above described data transmission system will be described below. 
     Initially, a peripheral device (not shown) is connected to the data transmission system 1 through the input terminal 6. If the signal output from the peripheral device is an RS-232C signal, and the switch 5 is positioned to connect the input terminal to the first interface 3, as shown in FIG. 1, the input terminal 6 is also connected to rectifier 14. As shown in FIG. 2, the anode of the diode 14a is biased at -10 V when a peripheral device outputs an RS-232C signal while connected to rectifier 14. This results in the LED 10a being forward biased and diodes 12a and 14a also being forward biased. Thus, the LED 10a emits light, indicating that an error has occurred. Since the erroneous connection is indicated, an operator can disable or switch the connection so that the signal (having a wider operating range than the first interface 3) is not continuously applied to the first interface 3. Therefore, no damage to the first interface 3 will occur. 
     If a peripheral device which outputs a TTL signal is connected to the input terminal 6, and the switch 5 is connected to the first interface 3, the voltage at the anode of the diode 14a is +5 V. The diode 14a is reversed biased, and, therefore, no current flows through the LED 10a, and light is emitted. Therefore, no error is indicated. 
     In case switch 5 is set to connect the input terminal 6 to the second interface 4, the rectifier 14 is not connected to the input terminal 6, and therefore, no error indication is made. The operating voltage range of the second interface 4 is designed, e.g., for an RS-232C signal, and as a result, if a peripheral device which outputs a TTL signal is erroneously connected to the second interface, no damage to the interface will occur. 
     As described above, the embodiment according to the present invention provides a visual indication of an erroneously connected peripheral device, which may damage the data transmission system if connected to the CPU 100. Thus, according to the present invention, damage of the data transmission system can be avoided. 
     In the disclosed embodiment, the first interface 3 is designed to receive TTL signals. Thus, depending on the design of the first interface 3, the first interface 3 may be damaged if RS-232C signals are applied, since the operating voltage range of the RS-232C signals is wider than the operating voltage of the first interface 3. Therefore, a protection circuit such as a clamping circuit, can be provided at the first stage of the first interface 3 in order to prevent the first interface 3 from being damaged. 
     Once it is determined that the peripheral device connected to the input terminal 6 is connected to the correct interface, then the error indicator 10 may be used to indicate erroneous data transmission from the peripheral device. 
     As shown in FIGS. 1 and 2, the output from the first interface 3 and second interface 4 is fed to the AND gate 2. The output of the AND gate 2 is fed to an input of the CPU 100. If the CPU 100 determines that the data output from the AND gate 2 is erroneous, the CPU 100 drives the switching circuit 7 to turn ON transistor 7a. The LED 10a is therefore forward biased, and emits light, indicating that an error has occurred. 
     Therefore, as described above, a single error indicator 10 (LED 10a) can be used to provide information about an erroneously connected peripheral device, as well as an error in data received from the peripheral device. This improves the functionality of the data transmission system. Further, the number of parts, cost and size of the data transmission system are reduced by this implementation. 
     Further, as described above, an indication of an erroneously connected peripheral device can be made even though the host computer is not connected, and an external power supply is not turned ON. This can prevent damage to the host computer, since the error can be corrected before the peripheral device is patched to the host computer. 
     The present disclosure relates to subject matter contained in Japanese Patent Application No. HEI 6-126797 filed on May 17, 1994 which is expressly incorporated herein by reference in its entirety.