JP2000092097A - System for insertion/withdrawal of live line in multi-bus system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain live line pull in and out for a terminal without giving effect on communication during the communication between optional terminals by applying live line pull in/out to the terminal being an object of live line pull in and out in a state that an interruption means is started to interrupt a corresponding signal line during the communication between the optional terminals. SOLUTION: In the case that an operation is made to connect an optional terminal 2k to a multi-terminal bus 1 or to disconnect an optional terminal 2k1 already connected from the multi-terminal bus 1 when terminals, e.g. 2a, 2b make communication with each other on the multi-terminal bus 1, each of bus interruption sections 3k-3k3 interrupts temporarily buses 4k-4k3 between the multi-terminal bus 1 and the terminals 2k-2k3. That is, the terminals 2k-2k3 are disconnected from the multi-terminal bus 1 by using the bus interruption sections 3k-3k3. Then the disconnected state is recovered as it was by the bus interruption sections 3k-3k3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-bus system in which a plurality of terminal devices are connected to one bus (hereinafter referred to as "multi-bus") via respective signal lines. The present invention relates to a hot-swap method for a multi-bus system that enables hot-swap of a terminal device without affecting the communication during communication between arbitrary terminal devices on a medium multi-bus system.

[0002]

2. Description of the Related Art Conventionally, in a multi-bus system of this kind, before the multi-bus system is started, a connection between the multi-bus and a terminal is made in advance, and an arbitrary connection between the multi-bus and an already connected multi-bus system is performed in accordance with a multi-bus protocol. Operate so as to perform communication between terminals (e.g., arbitrate between terminals to obtain the right to use the multibus, and use the bus for the terminal that has obtained the right to use the bus). It is common to do.

In a general terminal connected to the multi-bus, the electric level of the multi-bus interface signal terminal in the connection portion of the terminal connected to the multi-bus is (1) the power of the terminal is turned on and the terminal has already been started. In the state and the state where the power of the terminal is already turned off, the electric level of the multi-bus interface signal terminal keeps the high impedance, but when the power of the terminal is turned on and turned on and when the power is turned off, it is temporarily When the high impedance state is destroyed, and (2) when the power is turned on and started, the electrical level of the multi-bus interface signal terminal is high impedance,
At other times, the level can be roughly classified as unstable.

In the above conventional multi-bus system,
When communication is being performed between any terminal and a terminal, an attempt is made to activate (including the operation of connecting) a terminal other than the already activated terminal. (A) When connected to the multibus, noise is generated by contact between the multibus interface signal terminal on the multibus side and the multibus interface terminal on the terminal side.

(B) When a power supply of a terminal already connected to the multi-bus in a power-off state is turned on, noise is generated because the high-impedance state of the multi-bus interface terminal on the terminal side is destroyed.

Due to such factors, noise is applied to the multi-bus, and as a result, communication performed in the multi-bus system is disturbed, resulting in a disadvantage that access between terminals cannot be performed normally.

Conventionally, in order to avoid this inconvenience, a conventional multi-bus system in which communication is performed between arbitrary terminals is performed when a terminal is connected from the outside or when a power supply is already connected to the multi-bus. When turning on the power of a terminal that is not turned on, the multi-bus system must be temporarily stopped, then the terminal connection or power-on operation must be performed, and then the multi-bus system must be restarted. .

However, if the multi-bus system is stopped every time the terminal is connected and the power of the terminal connected to the multi-bus is turned on, the operation rate is significantly reduced. The problem arises.

[0009]

As described above, in the conventional multi-bus system, a new terminal device is newly added to the multi-bus system during communication between arbitrary terminal devices. When an additional connection or disconnection of a terminal device already connected to the bus system from the multi-bus system, or power-on or power-off of a terminal device already connected is performed, a multi-bus interface signal on the terminal device side is generated. From the terminals, noise is applied to the multi-bus system, and as a result, communication performed on the multi-bus system is disturbed.

For this reason, conventionally, in order to avoid communication disturbance due to the above-mentioned noise application, it is necessary to stop the multi-bus system once and then perform hot-swapping of the terminal device. However, there is a problem that the temperature is reduced.

Therefore, the present invention solves the above problem,
An object of the present invention is to provide a hot-swapping method for a multi-bus system that allows hot-swapping of a terminal device without affecting the communication during communication between arbitrary terminal devices on a multi-bus system in operation. And

[0012]

According to a first aspect of the present invention, there is provided a multi-bus system in which a plurality of terminal devices are connected to one bus via respective signal lines. Disconnection means for temporarily disconnecting each signal line between each terminal device, and activation means for activating the disconnection means during communication between any terminal devices via the signal line and the bus. Then, during communication between any of the terminal devices via the signal line and the bus, the disconnection unit is activated by the activation unit to disconnect the corresponding signal line. It is characterized in that hot-swapping of the device is performed.

According to a second aspect of the present invention, in the first aspect of the present invention, the activation means detects power on / off detection means for detecting when the terminal device is turned on and when the terminal device is turned off. And activation control means for activating the disconnection means when the power on / off detection is detected by the power on / off detection means.

According to a third aspect of the present invention, in the first aspect of the present invention, a switch means for operating the cutting means by a user, and a switch operation of the switch means,
Starting control means for starting and controlling the disconnecting means.

According to a fourth aspect of the present invention, in the first aspect of the invention, the activating means detects power-on / off detecting means for detecting when the terminal device is turned on and when the terminal device is turned off. Switch means for operating the disconnection means by a user; and activation control means for controlling activation of the disconnection means based on a detection result of the power on / off detection means and a switch operation of the switch means. It is characterized by the following.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a diagram showing an overall configuration of a multibus system according to an embodiment of the present invention.

In FIG. 1, the multi-bus system includes a multi-terminal bus 1, multi-terminal bus terminals 2a to 2n, bus disconnecting sections 3a to 3n, and buses 4a to 4n on the terminal side. I have.

The multi-terminal bus 1 is a signal path (bus) commonly used by a plurality of terminal devices 2a to 2n to be connected, and transmits a signal from each terminal.

The terminal devices 2a to 2n are terminal devices connected to and accommodated in the multi-terminal bus 1.

The bus disconnecting sections 3a to 3n are characteristic parts of the present invention, and disconnect the terminal devices 2a to 2n connected to the respective bus disconnecting sections 3a to 3n and the buses 4a to 4n on each terminal device side. The terminal devices 2a to 2n and the multi-terminal bus 1 are temporarily disconnected. In addition, this bus cutting part 3a
.About.3n have a function of recovering the state before the bus disconnection after temporarily disconnecting the bus.

Next, a general operation in the case of performing point-to-point communication in such a multi-bus system will be described with reference to an example in which the terminal device 2a and the terminal device 2b perform communication.

In FIG. 1, a terminal device 2a sends information to a terminal device 2b. The information transmitted from the terminal device 2a is transmitted to the multi-terminal bus 1 via the bus 4a on the terminal device side, the bus disconnecting unit 3a.

The information transmitted on the multi-terminal bus 1 is transmitted through each of the bus disconnecting sections 3b to 3n other than the bus disconnecting section 3a and the buses 4b to 4n on each terminal device side. Is transmitted to each of the terminal devices 2b to 2n.

Next, each of the terminal devices 2b to 2n refers to the destination information added to the header information of the received information, and performs a process of fetching the information only if the information is for itself.

In this case, the transmitted information is information destined for the terminal device 2b. Therefore, the terminal device 2b checks the header of the received information to confirm that the information is destined for itself, and take in.

The above operation is an outline of information transmission on a general multi-terminal bus 1. Next, the terminal device 2a and the terminal device 2 are temporarily stored on the multi-terminal bus 1.
(b) When communicating with the multi-terminal bus 1 (a) Connect any terminal device 2k to the multi-terminal bus 1 (a) Disconnect any terminal device 2k1 already connected from the multi-terminal bus 1 ( C) Turn on the power of the terminal device 2k2 which is already connected to the multi-terminal bus 1 and which is turned off. (D) The terminal device which is already connected to the multi-terminal bus 1 and the power is on. When an operation such as turning off the power of the terminal device 2k3 is performed, when the terminal devices 2k to 2k3 apply the noise to the multi-terminal bus 1, each bus is disconnected. Part 3k-3k
3 temporarily disconnects the multi-terminal bus 1 and the buses 4k to 4k3 on the terminal device side, respectively. In other words, the terminal devices 2k to 2k3 are cut off from the multi-terminal bus 1 at the bus disconnecting sections 3k to 3k3. Thereafter, the bus disconnecting sections 3k to 3k3 recover from the disconnected state.

Since each unit operates as described above, by providing a bus disconnecting unit between the multi-terminal bus and the terminal device, the bus disconnecting unit is activated when the terminal device is connected to or disconnected from the multi-terminal bus. By doing so, it is possible to disconnect the multi-terminal bus from the terminal-side bus, thereby enabling "hot plugging and unplugging of the multi-terminal bus interface" without interrupting active communication.

FIG. 2 is a schematic diagram showing a mounting structure of the multi-terminal bus interface shown in FIG. As shown in FIG. 2, this multi-terminal bus interface includes a daughter board (daughter
oard) 11 (11a to 11n) is inserted. The multi-terminal bus 1 is provided inside the motherboard 10. Daughter board 11 (11a-
11n) accommodates the terminal devices 2a to 2n for the multi-terminal bus 1 shown in FIG. 1, the bus disconnecting sections 3a to 3n, and the buses 4a to 4n on the terminal device side.

This daughter board 11 (11a-11)
The flow of signals when communicating between n) will be described by taking as an example a case where communication is performed from the daughter board 11a to the daughter board 11n. In FIG. 2, first, the signal transmitted by the terminal device accommodated in the daughter board 11a is:
The signal passes through the bus on the terminal device side in the daughter board 11a and the bus cutting section, and reaches the motherboard 10. Motherboard 1
The signal that has reached 0 flows through a transmission line (multi-terminal bus) laid in the motherboard 10. This signal enters each of the daughter boards 11a to 11n, and is transmitted in the order of the bus disconnection section, the terminal-side bus, and the terminal device in the daughter board 11n.

Next, a mechanism for inserting and removing the daughter board 11 will be described. Daughter board 11
The power supply is turned on at the same time as the power supply is inserted into the motherboard 10, and is turned off at the same time as the power supply is removed from the motherboard 10.

(1) When the daughter board 11 is inserted, at the same time, the bus disconnecting section accommodated in the daughter board 11 is in a disconnected state (a state in which the multi-terminal bus and the terminal-side bus are electrically disconnected). )become. In this state, the terminal device starts up (becomes operable).
After the terminal device has started up, the bus is switched to the connected state. The determination as to whether or not the terminal device has started up is performed by (A) measuring the time until the terminal device starts up in advance, and determining the time during which the bus disconnecting unit disconnects the bus.
It is set longer than this time, and the voltage level in the daughter board 11 is constantly monitored, and when the voltage rises above the threshold (this also applies to the state at power-on).
(B) A switch for requesting a bus disconnection from a bus disconnection section is provided in the daughter board, and the bus is determined by the electrical level of the switch (when a disconnection request is issued). There is a method of judging to disconnect. Bus disconnection is determined based on the logical sum of (A) and (B). FIG. 7 shows a logical sum table at this time.

(2) When detaching the daughter board 11 from the motherboard 10, the bus disconnecting section in the daughter board 11 disconnects the multi-terminal bus and the terminal-side bus. It should be noted that the determination as to whether or not to make the disconnection state includes (a) a method of constantly monitoring the voltage level in the daughter board 11 and determining to disconnect the bus when the voltage falls below the threshold value; There is a method in which a switch or the like for requesting a bus disconnection is provided in a bus disconnection section in the daughter board 11, and it is determined that the bus is disconnected based on the electric level of the switch (when a disconnection request is issued). Bus disconnection is determined based on the logical sum of (a) and (b).
FIG. 8 shows a logical sum table at this time.

According to such a configuration, the bus can be temporarily cut off when the daughter board is inserted and removed (when the power of the already connected terminal is turned on or turned off), so that no noise is applied to the multi-terminal bus. Terminal device can be connected to or disconnected from the terminal device.

FIG. 3 shows the daughter board 11 shown in FIG.
It is a block diagram which shows the whole structure of (11a-11n). As shown in FIG. 3, the daughter board 11 (11
a to 11n) are the terminal device 110 and the bus disconnecting unit 111
, A connector 112, and a switch 113.

Here, the terminal device 110 is a terminal connected to each of the daughter boards 11a to 11n.

The bus disconnecting unit 111 is a terminal
In order to separate the bus on the side from the motherboard 10, the bus is disconnected.

The connector 112 is connected to each daughter board 11.
a to 11n and the motherboard 10.

The switch 113 controls the activation of the bus disconnection unit 111 by a user operation. When the switch 113 is turned on, the bus disconnection request signal (S1) is enabled (that is, the bus disconnection unit). 111), and the switch is set to O
In the FF state, the bus disconnection request signal (S1) is disabled (that is, a signal that does not operate the bus disconnection unit 111). The switch 113 is provided at a location where an operator who connects or disconnects the terminal device 110 can easily operate the switch.

Next, the daughter boards (11a to 11a)
n) is inserted into or removed from the motherboard 10.

First, when inserting or removing the daughter board (any one of 11a to 11n) from motherboard 10, switch 113 must be turned on in advance.
It is performed after the state (that is, the state in which the bus disconnection of the bus disconnection unit 111 is operated). At this time, the bus disconnection request signal (S1) from the switch 113 is enabled, the bus disconnection unit 111 is activated, and connection and disconnection of the daughter boards (11a to 11n) and the motherboard 10 can be performed with the bus disconnected. it can. (In addition, (A)
If the daughter board is powered on in advance, it is connected to the motherboard with the bus disconnected from the beginning. In the case of (B) a system in which the power is turned on by connecting the daughter board to the motherboard, the bus is turned off at the same time as the power is turned on. According to such a configuration, the daughter board is provided with a bus disconnection section for disconnecting the terminal device and the multi-terminal bus, and a switch for activating the bus disconnection section is provided. Daughter boards can be inserted or removed.

FIG. 4 is a block diagram showing the overall configuration of the bus cutting unit 111 shown in FIG. As shown in FIG. 4, the bus disconnection unit 111 includes a power-on monitoring unit 111a, a bus disconnection request monitoring unit 111b, an OR circuit 111c,
And a bus disconnecting function unit 111d.

Here, when the power is supplied to the daughter boards 11 (11a to 11n), the power-on monitoring section 111a activates the power-on signal (S2) shown in FIG. Signal indicating that).

The bus disconnection request monitoring section 111b monitors the bus disconnection request signal (S1) from the switch 113 shown in FIG. 3, and when this signal indicates an enable state, the bus disconnection start signal (S1) shown in FIG. S3) is enabled.

The OR circuit 111c receives the power-on signal (S2) and the bus disconnection start signal (S3), executes a logical sum, and outputs a bus disconnection signal (S4) (enables the bus). The OR circuit 111c at this time
9 is shown in FIG.

Upon receiving the bus disconnection signal (S4), the bus disconnection function section 111d disconnects the multibus and electrically or physically disconnects the terminal device 110 from the multibus.

Next, the detailed operation of each of the above components will be described.

First, when the power is turned on, the power-on monitoring unit 111a enables the power-on signal (S2) until a device on the same daughter board is started, and after the device is started, , Power-on signal (S
Disable 2). By operating in this way, the bus disconnection signal (S
4) is enabled), the power is turned on, and the terminal device 1 is turned on.
Until 10 starts, the terminal device 110 can be separated from the multibus.

In the bus disconnection request monitoring unit 111b, the switch 113 shown in FIG.
When the bus disconnection request signal (S1) from the switch 13 is enabled, the bus disconnection start signal (S3) is enabled. Conversely, the switch 113 shown in FIG. When S1) is disabled, the bus disconnection start signal (S3) is disabled. By operating in this manner, the daughter board 1
When inserting or removing 1 (11a to 11n), the terminal device 110 can be reliably separated from the multibus.

The operation of the OR circuit 111c is shown in the table of FIG. As can be seen from this figure, the power-on signal (S
2) and / or the bus disconnection start signal (S3) is enabled (ON state), the bus disconnection signal (S3)
4) is enabled (ON state) and the power-on signal (S
When both 2) and the bus disconnection start signal (S3) are disabled (OFF state), the bus disconnection signal (S4) is disabled (OFF state). By operating in this manner, the bus disconnection signal (S4) can be output according to the states of the power-on signal (S2) and the bus disconnection start signal (S3) shown in FIG.

The bus disconnecting function section 111d disconnects the bus only when the bus disconnection request signal (S1) is enabled.

FIG. 5 shows the power-on monitoring section 111 shown in FIG.
It is a block diagram which shows the whole structure of a. As shown in FIG. 5, in the power-on monitoring section 111a, the voltage detecting section 11
1a1, a bus disconnection time counting section 111a2, and a bus disconnection signal sending section 111a3.

Here, the voltage detector 111a1 detects a rise and a drop of the power supply voltage in the same daughter board. The judgment of the rise of the power supply voltage is based on the fact that the power supply voltage is at a certain threshold value (this is a device on the same daughter board (see FIG. 3)
Should be set on the basis of the lower limit value of the operating voltage, and must be set to a voltage lower than the lower limit value. ) Is judged. Thereby, the voltage detection unit 111a1
Detects the rise of the power supply voltage in the same daughter board and enables the threshold signal (S5) shown in FIG.
On the other hand, the determination of the drop in the power supply voltage is such that the power supply voltage is set to a certain threshold value (threshold at the time of the drop) (a voltage higher than the lower limit value of the operating voltage of the terminal device 110 shown in FIG. 3).
Judge by going below. As a result, the voltage detection unit 111a1 detects a drop in the power supply voltage in the same daughter board, and disables the threshold signal (S5) shown in FIG. In other words, the threshold signal (S5) indicates that a change in the power state of the same daughter board indicates that the power supply has changed from OFF to ON
Is enabled by the change of
The state is disabled by the change of F.

When the logic level of the threshold signal (S5) changes to the enable state (that is, when the power supply of the daughter board is turned on), the bus disconnection time counting section 111a2 sets a predetermined time ( A time-out signal (S6) is enabled, which is a time period much longer than the rise time at the time of power-on of the devices in the same daughter board. Then, after a predetermined time has elapsed, the signal is disabled. On the other hand, when the threshold signal (S5) is in the disabled state, the timeout signal (S6) is held in the enabled state. That is, when the power supply in the same daughter board changes to the ON state, the timeout signal (S6) is enabled for a certain period of time, and thereafter is maintained in the disabled state. Also, the power is off
When it changes to the state, it is kept in the enabled state.

The bus disconnection signal transmission section 111a3 adjusts the electrical level of the timeout signal (S6) to the TTL level and transmits the power-on signal (S2) (that is, the bus disconnection signal).

FIG. 6 shows the bus disconnection request monitoring unit 1 shown in FIG.
It is a block diagram which shows the whole structure of 11b. As shown in FIG. 6, the bus disconnection request monitor 111b includes a bus disconnection control signal generator 111b1 and a waveform forming circuit 111b.
2. It is configured to include a bus disconnection start signal transmission unit 111b3.

Here, the bus disconnection control signal generator 111b
1 receives the bus disconnection request signal (S1) from the switch 113 shown in FIG. 3, removes spike noise applied to the bus disconnection unit 111 from the signal, and sends out a bus disconnection control signal (S7). This bus disconnection control signal (S7) changes in conjunction with the logical level of the bus disconnection request signal (S1). That is, when the bus disconnection request signal (S1) is in the enable state, the bus disconnection control signal (S1) transmitted from the bus disconnection control signal generation section 111b1.
7) is enabled, and when the bus disconnection request signal (S1) is disabled, the bus disconnection control signal (S7) is disabled. The waveform forming circuit unit 111b2 receives the bus disconnection control signal (S7) and forms a signal waveform of the signal so that the next block can easily recognize the signal (electrical level and transmission pattern). . The formed waveform is output to the next stage as a bus disconnection start request signal (S8). The source of the bus disconnection control signal (S7) received by the waveform forming circuit 111b2 may be a switch of a mechanical contact. In this case, when the electrical level of the signal rises and falls, the electrical level may be disturbed (a region where the signal level is uncertain). The purpose is to eliminate the disturbance of the electric level. When an arbitrary electric level of the signal has continued for a certain period of time (it is ideally made variable depending on the source of the signal. In the case of a mechanical contact, several milliseconds are required). ), A bus disconnection start request signal (S8) is transmitted. The bus disconnection start request signal (S8) changes in conjunction with the bus disconnection control signal (S7). That is, when the bus disconnection control signal (S7) is enabled, the bus disconnection start request signal (S8) is enabled and the bus disconnection control signal (S7) is enabled.
7) is disabled, the bus disconnection start request signal (S
8) is disabled.

The bus disconnection start signal transmitting section 111b3 adjusts the electric level of the bus disconnection start request signal (S8) to the TTL level and transmits the bus disconnection start signal (S3).

As a specific application of this embodiment described above, an interface such as SCSI or Ethernet can be considered.

[0060]

As described above, according to the present invention,
Disconnecting means for temporarily disconnecting each signal line between the multi-bus (bus) and each terminal device is provided, and when performing hot-swapping of the terminal device, the disconnecting device is activated and the corresponding signal line is activated. In the state where the terminal is disconnected, the terminal device to be hot-swapped is inserted and removed, so that even when communication is performed between any terminal devices on the operating multi-bus system, the communication can be performed. Without hindering the operation, the hot swap of the terminal device can be performed, and the inconvenience that the operation rate is reduced by performing the hot swap of the terminal device after the system is cut off is prevented as in the related art. For example, it is possible to prevent the communication time from being excessively increased due to repeated retransmission operations due to communication disconnection.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a multibus system according to an embodiment of the present invention.

FIG. 2 is an external schematic view showing a mounting structure of the multi-bus system shown in FIG.

FIG. 3 is a block diagram showing an overall configuration of daughter boards 11a to 11n shown in FIG. 2;

FIG. 4 is a block diagram showing an overall configuration of a bus cutting unit shown in FIG. 3;

FIG. 5 is a block diagram showing the overall configuration of a power-on monitoring unit in FIG.

FIG. 6 is a block diagram showing an overall configuration of a bus disconnection request monitoring unit shown in FIG. 4;

FIG. 7 is a table showing a logical sum operation in the bus cutting unit shown in FIG. 2;

FIG. 8 is a table showing another example of the OR operation in the bus disconnection unit shown in FIG. 7;

FIG. 9 is a table showing the operation of the OR circuit shown in FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Multi-terminal bus 2a-2n Terminal device 3a-3n Bus disconnecting unit 4a-4n bus 10 Motherboard 11 (11a-11n) Daughter board 110 Terminal device 111 Bus disconnecting unit 111a Power-on monitoring unit 111a1 Voltage detecting unit 111a2 Bus disconnecting time count Unit 111a3 bus disconnection signal transmission unit 111b bus disconnection request monitoring unit 111b1 bus disconnection control signal generation unit 111b2 waveform formation circuit unit 111b3 bus disconnection start signal transmission unit 111c OR circuit 111d bus disconnection function unit 112 connector 113 switch

 ────────────────────────────────────────────────── ─── Continued from the front page (72) Inventor Hiroshi Yamaguchi 3-1-1 Asahigaoka, Hino-shi, Tokyo Toshiba Communication Systems Engineering Co., Ltd.

Claims (4)

[Claims] In a multi-bus system in which a plurality of terminal devices are connected to one bus via respective signal lines, disconnection for temporarily disconnecting each signal line between the bus and each terminal device is provided. Means, during communication between any of the terminal devices via the signal line and the bus, comprising a starting means to start the disconnecting means,
During communication between any of the terminal devices via the signal line and the bus, the disconnection unit is activated by the activation unit,
A hot-swap method for a multi-bus system, wherein hot-swap of a terminal device to be hot-swapped is performed in a state where a corresponding signal line is cut. 2. The power-on / off detection means for detecting when the power of the terminal device is turned on and when the power is turned off, and a detection result of the power-on / off detection means. 2. The hot-swap method for a multi-bus system according to claim 1, further comprising: a start-up control unit that controls the start-up of said disconnection unit. 3. The apparatus according to claim 2, wherein said activation means includes: switch means for operating said disconnection means by a user; and activation control means for activationly controlling said disconnection means based on a switch operation of said switch means. The hot-swap method for a multi-bus system according to claim 1, wherein 4. The power-on / off detection means for detecting when the power of the terminal device is turned on and when the power is turned off; a switch means for operating the disconnection means by a user; 2. The multi-bus system according to claim 1, further comprising: start control means for controlling start of said disconnection means based on a detection result of said power on / off detection means and a switch operation of said switch means. Hot swapping method.