JPH0991069A - Expansion bus control circuit - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide an expansion connector that does not cause unnecessary radiation of radio waves even when an external expansion device is not connected to the external expansion connector. SOLUTION: An input bus signal S1 to a personal computer is directly input to the personal computer 1. The output bus signal S2 is output from the expansion connector 3 to the expansion device 4 as the same signal S3 output controlled by the buffer circuit 21. The enable signal of the buffer circuit 21 is used as the connection detection signal S4 by pulling up the ground signal of the expansion device to the constant voltage VCC by the pull-up resistor 26 in the expansion connection unit 2. Input / output bus signal S8 other than data and data input / output bus signal S13
Similarly, the output is controlled by the bidirectional buffer circuits 22 and 24, respectively, and the signals S7 and S14 are connected to the expansion device 4 through the expansion connector 3. Bidirectional buffer circuit 22
The enable signals of 24 and 24 can be used by sharing the previous connection detection signal S4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an extended bus control circuit for use in personal computers and the like, which reduces unnecessary radiation.

[0002]

2. Description of the Related Art A personal computer has an external bus slot for connecting various kinds of expansion boards, but for connecting external expansion equipment so that more expansion boards can be connected. There is an extension connector terminal that draws out the bus signal of the outside. In this case, conventionally, the bus signal was directly drawn out to the expansion connector terminal, so even when the external expansion device is not connected to the connector terminal, the bus signal composed of many signals such as the power supply voltage is output to the expansion connector. Since they were on board, these bus signals became sources of unnecessary radiation of radio waves, and there was a risk that countermeasures would be required.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and is an expansion device that does not cause unnecessary radiation of radio waves even when an external expansion device is not connected to the external expansion connector. To provide a connector.

[0004]

An expansion connector having an expansion connector is provided with bus signal control means connected to the expansion connector, and the connection of the expansion connector to an external expansion device connected to the expansion connector is shown. A connection detection signal generating means is provided to prohibit output of the bus signal to the expansion connector when an external expansion device is not connected to the expansion connector.

When the bus signal control means connected to the expansion connector is a buffer circuit inserted in the bus signal, and the connection detection signal is an enable signal for the buffer circuit, and an external expansion device is not connected to the expansion connector. Prohibits bus signal output to the expansion connector.

The means for generating the connection detection signal is a ground signal provided in an external expansion device, and the ground signal pulled up by connecting the ground signal to a constant voltage source via a resistor at the expansion connection section is used for the buffer circuit. The enable signal.

The master signal indicating the bus usage state of the equipment connected to the bus signal is used to control the input / output direction of the buffer circuit for input / output signals other than the data line of the bus signal.

A latch circuit for holding one of the data lines of the bus signal is provided to control the input / output direction of the buffer circuit of the data line of the bus signal.

[0009]

In the expansion connecting portion having the expansion connector, the bus signal control means connected to the expansion connector is provided, and the external expansion equipment connected to the expansion connector is connected to the expansion detection means to generate a connection detection signal. By disabling the bus signal output to the expansion connector when the external expansion device is not connected to the expansion connector, the external expansion device is connected to the expansion connector when the external expansion device is not connected. Since no bus signal is output to the connector, unnecessary radiation of radio waves is eliminated.

When the bus signal control means connected to the expansion connector is a buffer circuit inserted into the bus signal, and the connection detection signal is used as an enable signal for the buffer circuit, an external expansion device is not connected to the expansion connector. By prohibiting output of bus signals to the expansion connector, multiple bus boards can be connected to external expansion equipment, and noise superposition on bus signals is reduced.

The connection detection signal can be easily obtained by using the ground signal provided in the external expansion device as the means for generating the connection detection signal and pulling up the ground signal at the expansion connection portion to use as the enable signal for the buffer circuit. To be

By controlling the input / output direction of the buffer circuit for the input / output signals other than the data line of the bus signal by using the master signal indicating the bus usage state of the device to which the bus signal is connected, the direction control of the bus buffer is performed. Can be done easily.

By providing a latch circuit for holding one of the data lines of the bus signal and controlling the input / output direction of the buffer circuit of the data line of the bus signal, it is possible to control the data bus buffer without fine timing control. Input / output direction control is possible.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An expansion bus control circuit according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram of an expansion bus control circuit according to the present invention. PC body 1
Each bus signal input to and output from the device passes through the expansion connection unit 2 and is connected to the expansion device 4 via the expansion connector 3. Of the bus signals, the input bus signal S1 to the personal computer is directly input to the personal computer 1 because it is not necessary to control the output. The output bus signal S2 of the personal computer is supplied to the buffer circuit 21.
Expansion connector 3 as the same signal S3 output controlled by
To the expansion device 4. As an enable signal for the buffer circuit 21, a ground signal grounded by the expansion device is pulled up to a constant voltage VCC by a pull-up resistor 26,
It is used as the connection detection signal S4. Similarly, the output control of the input / output bus signal S8 and the data input / output bus signal S13 other than the data is performed by the bidirectional buffer circuits 22 and 24, and are connected to the expansion device 4 through the expansion connector 3 as the same signals S7 and S14, respectively. . Bidirectional buffer circuits 22 and 2
The enable signal of No. 4 shares the previous connection detection signal S4 and is used. Bidirectional buffer circuit 2 for input / output bus signal S8 other than data with simple switching timing of input / output period
As the direction control signal of No. 2, the open collector signal S5 from the expansion device indicating the usage status of the expansion device is pulled up to the constant voltage VCC by the pull-up resistor 27 and used. The signal is connected to the personal computer 1 via the open collector circuit 28. On the other hand, the direction control signal of the bidirectional buffer circuit 24 for the data input / output bus signal S13 with complicated switching timing of the input / output period is created and used by the firmware of the personal computer and the expansion device. On the personal computer side, one of the same data signals when outputting data, S8
Is latched by the latch circuit 23, and the logic 0 signal S9 is connected to the signal S12 via the AND circuit 25 to the direction control terminal of the buffer circuit 24. At this time, assuming that the direction control signal of the buffer circuit 24 is logic 0 and the output direction is from the personal computer, the data signal S13 is output as the same signal S14. The output S9 of the latch 23 is logic 1 except when the output is from the personal computer. When the output data is input to the personal computer 1 from the expansion device, one of the data signals S11 is latched by the expansion device 4 by the latch circuit 41, and the output S10 is input to the AND circuit 25. At this time, the direction control signal S12 becomes logic 1 and the data is input to the personal computer.

[0015]

As described above, in a personal computer to which an expansion connector is attached and an expansion device is connected, the expansion connection portion having the expansion connector is provided with bus signal control means connected to the expansion connector. An external expansion device connected to the expansion connector is provided with a connection detection signal generating means for indicating the connection of the same, and when the external expansion device is not connected to the expansion connector, a bus signal output to the expansion connector By prohibiting, the unnecessary radiation from the expansion connector can be reduced, and the reliability and safety of the device can be increased.

[Brief description of drawings]

FIG. 1 is a block diagram of an expansion bus control circuit according to the present invention.

[Explanation of symbols]

 1 PC main body 2 Expansion connection section 3 Expansion connector 4 Expansion equipment 21 Buffer circuit 22 Bidirectional buffer circuit 23 Latch circuit 24 Bidirectional buffer circuit 25 AND circuit 26 Resistor 27 Resistor 28 Open collector circuit 41 Latch circuit VCC Constant voltage S1 input Bus signal S2 Output bus signal S3 Output bus signal S4 Ground signal S5 Master signal S6 Input / output bus signal other than data S7 Input / output bus signal other than data S8 Data signal S12 Direction control signal S13 Data input / output signal S14 Data input / output signal

Claims (5)

[Claims] 1. A personal computer having an expansion connector having an expansion connector for expanding the bus signal of the personal computer to the outside in a personal computer, and controlling the bus signal connected to the expansion connector at the expansion connector. Means is provided, the external expansion device connected to the expansion connector is provided with a means for generating a connection detection signal indicating the connection of the device, and when the external expansion device is not connected to the expansion connector, the external expansion device is connected to the expansion connector. Expansion bus control circuit characterized by prohibiting the bus signal output of. 2. A bus signal control means connected to the expansion connector is a buffer circuit inserted in the bus signal, and an external expansion device is connected to the expansion connector by using the connection detection signal as an enable signal for the buffer circuit. 2. The expansion bus control circuit according to claim 1, wherein the bus signal output to the expansion connector is prohibited when the expansion bus control circuit does not exist. 3. The connection detection signal generating means is a ground signal provided in an external extension device, and the ground signal is connected to a constant voltage source via a resistor at the extension connection portion to enable the buffer circuit. The expansion bus control circuit according to claim 2, wherein the expansion bus control circuit is a signal. 4. The input / output direction control of a buffer circuit for an input / output signal other than a data line of the bus signal is performed by using a master signal indicating a bus usage state of a device to which the bus signal is connected. The expansion bus control circuit according to claim 2 or claim 3. 5. The method according to claim 2, wherein a latch circuit for holding one of the bus signal data lines is provided to control the input / output direction of the buffer circuit for the bus signal data line. The expansion bus control circuit according to item 4.