JPH06149429A - Pull-up resistor switching circuit - Google Patents

Abstract

PURPOSE:To miniaturize a computer unit to connect plural external input/output devices provided with different impedance standards, and to provide the pull-up resistor switching device which prevents a computer from generating malfunction or destroying circuit elements. CONSTITUTION:This circuit is provided with a shared connector 35 for connecting the plural external input/output devices, impedance switching means 18, 31, 32 and 34 for satisfying the different impedance standards of those plural external input/output devices, and leaked current proof means (diode) 33 for preventing the circuit element destruction or malfunction of a computer 10 due to leaked potentials from the external input/output devices.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pull-up resistance switching circuit, and more particularly to a pull-up resistance switching circuit for connecting a plurality of external input / output devices having different impedance standards.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram of a conventional computer system having a pull-up resistor for connecting a computer and a plurality of external input / output devices.

In the figure, a conventional computer system of this type comprises a computer 10 and a plurality of external input / output devices 11 and 12, and the computer 10 includes a data processing circuit 13, an input / output buffer 14, and a bidirectional. The signal line 15, the input signal line 16, the power supply voltage 17, the pull-up resistor 18 for the external input / output device 11, the pull-up resistor 19 for the external input / output device 12, and the signal line 20. There is. Further, the external input / output device 11 includes a power supply voltage 23, a resistor 24, and an input / output buffer 25,
The external input / output device 12 includes an output buffer 26. The computer 10 and the external input / output devices 11 and 12 are connected to each other by the connectors 21 and 22.

The operation of the pull-up resistor of the conventional computer system configured as described above will be described. As is apparent from the figure, the conventional computer system has a plurality of connectors 21 and 22 corresponding to the plurality of external input / output devices 11 and 12. Then, the input / output data from the external input / output device 11 is input to the connector 21 and the signal line 2
Input / output is performed to the input / output buffer 14 via 0, and impedance adjustment with the external input / output device 11 is performed by the pull-up resistor 18. Input data from the external input / output device 12 is input to the data processing circuit 13 via the connector 22 and the input signal line 16, and the pull-up resistor 19 is supplied.
Therefore, impedance adjustment with the external input / output device 12 is performed.

[0005]

In the conventional pull-up resistor switching circuit, as described above, the individual connectors and pull-up resistors are configured in correspondence with the respective external input / output devices. In a computer system in which a large number of external input / output devices are connected to a large number of data processing circuits, a plurality of external input / output devices are always required to have a plurality of connectors, which has been a major obstacle to the miniaturization of the device. When the power of the computer is OFF and the power of the external input / output device is ON, the power supply voltage of the external input / output device floats the power supply voltage of the computer through the resistance of the own device and the pull-up resistor of the computer, However, there is a problem in that the malfunction of the device or the destruction of the circuit element is caused.

The present invention has been made in order to solve the above problems, and realizes miniaturization of a computer device by sharing a connector for connecting a plurality of external input / output devices which are rarely used. In addition, the power of the computer is turned off and the power of the external input / output device is turned on.
Even in the case of N, the purpose is to obtain a pull-up resistor switching circuit that does not cause a computer to malfunction or destroy circuit elements.

[0007]

In order to achieve the above object, a pull-up resistance switching circuit according to the present invention includes a common connector for connecting a plurality of external input / output devices and a plurality of external input / output devices. The present invention is characterized by comprising impedance switching means satisfying different impedance standards and leakage current prevention means for preventing malfunction due to leakage potentials from a plurality of external input / output devices.

[0008]

Therefore, according to the pull-up resistance switching circuit of the present invention, a plurality of external input / output devices having different impedance standards can be connected by the common connector and the impedance switching means while maintaining the miniaturization of the device. Moreover, the leakage current prevention means enables the computer to be connected without causing malfunction or destruction of circuit elements even when the computer is powered off and the external input / output device is powered on.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a computer system that constitutes a pull-up resistance switching circuit according to this embodiment. In the figure, the same or corresponding parts as those of the conventional computer system are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 1, in the computer system of this embodiment, the computer 10 includes resistors 31, 34 and M
The OS FET 32, the diode 33, and the data processing circuit 13 are provided, and the external input / output device 11 and the external input / output device 12 are connected to the computer 10 by a common connector 35. In addition, an enable signal of the signal line 20 which is an output signal from the data processing circuit 13 is shown in FIG.
Is shown as enable signal 30.

Next, the operation of the computer system of the present embodiment configured as described above will be described. First, when the external input / output device 11 is connected to the computer 10, the data processing circuit 13 turns on the enable signal 30 of the signal line 20. As a result, the input / output buffer 14 becomes data enable, and the signal line 20 becomes the bidirectional signal line 1.
It becomes conductive with 5. Therefore, the data processing circuit 13 and the external input / output device 11 are in a connected state in which data can be input / output through the shared connector 35.

Regarding the pull-up resistance value at that time, the enable signal 3 of the signal line 20 from the data processing circuit 13 is used.
When 0 is applied to the base of the MOS FET 32 via the resistor 31, the MOS FET 32 is turned on, whereby the resistor 34 and the resistor 18 are connected in parallel, and the combined resistance value thereof is the same as the value of the resistor 19 in FIG. Designed to be equivalent. Therefore, it is understood that the pull-up resistance switching circuit of this embodiment can satisfy the impedance standard of the external input / output device 11.

Also, the computer 10 has a common connector 3
When the external input / output device 12 is connected via 5, the enable signal 30 of the signal line 20 from the data processing circuit 13
Is turned off. As a result, the input / output buffer 14 becomes data disable, and the signal line 20 becomes the input signal line 16
Then, the signal line 20 realizes the same function as the input signal line 16 shown in FIG. 2, and the input data can be processed by the data processing circuit 13.

Regarding the pull-up resistance value at that time, the enable signal 3 of the signal line 20 from the data processing circuit 13 is used.
Since 0 is turned off, the MOS FET 32 is turned off and only the resistor 18 is connected to the power supply voltage 17. Therefore, the combined resistance value in this case becomes equal to the value of the resistor 19 in FIG. 2, and it is understood that the pull-up resistance switching circuit of this embodiment can satisfy the impedance standard of the external input / output device 12. The diode 33 and the MOS FE of the pull-up resistance switching circuit of this embodiment are
The ON resistance of T32 should be small enough to be ignored with respect to the impedance standard of a plurality of external input / output devices.

Further, for example, when the external input / output device 11 and the computer 10 are connected, the external input / output device 11
Is connected to the power supply voltage 23 through the resistor 24, the power supply voltage 17 of the computer 10 becomes O.
In the FF state, the power supply voltage 23 of the external input / output device 11 is turned on.
In the state, the leakage current from the power supply voltage 23 of the external input / output device 11 causes the resistance 24, the common connector 35, and the signal line 2 to flow.
Although the circuit configuration is such that it flows into the power supply voltage 17 of the computer 10 via 0 and the resistor 18 or the resistor 34 (this has conventionally caused malfunction of the computer or destruction of circuit elements). In the pull-up resistor switching circuit of the example, this leakage current is prevented by the diode 33.

[0016]

As described above, according to the pull-up resistance switching circuit of the present invention, a plurality of external input / output devices having different impedance standards are connected by the common connector, and the different impedances of the external input / output devices are connected. Since the standard is configured to be satisfied by the impedance switching means, there is an effect that a plurality of external input / output devices having different impedances can be connected while maintaining the miniaturization of the computer device. Also, when the computer power is off and the external input / output device power is on,
Since the leakage current generated in the case of N is configured to be prevented by the leakage current prevention means, there is an effect that it is possible to prevent the malfunction of the computer and the destruction of the circuit element.

[Brief description of drawings]

FIG. 1 is a block diagram of a computer system including a pull-up resistance switching circuit according to an embodiment.

FIG. 2 is a block diagram of a computer system for connecting a plurality of external input / output devices having conventional pull-up resistors.

[Explanation of symbols]

 10 computer 11,12 external input / output device 13 data processing circuit 14,25 input / output buffer 15 bidirectional signal line 16 input signal line 17,23 power supply voltage 18,19,24,31,34 resistance 20 signal line 21,22 connector 26 Output Buffer 32 MOS FET 33 Diode 35 Shared Connector

Claims (1)

[Claims] 1. A pull-up resistor switching circuit used in a computer system for connecting a plurality of external input / output devices each having a different impedance standard, wherein a shared connector for connecting the plurality of external input / output devices is provided.
Impedance switching means satisfying different impedance standards of the plurality of external input / output devices, and leakage current prevention means for preventing circuit element destruction or malfunction due to leakage potential from the plurality of external input / output devices are provided. A pull-up resistor switching circuit.