JPH10301898A - Electronic equipment and interface circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to use the electronic equipment as both a host and a guest. SOLUTION: Relating to the electronic equipment having the interface circuit for connecting other equipment, the interface circuit is equipped with connectors 30 and 32 provided with terminals for connecting a data line, bidirectional line drivers 36 and 38 which send and receive signals through the data line, a path part 34 provided with paths between the connectors 30 and 32 and corresponding line drivers 36 and 38 and a path between terminals of the connectors 30 and 32, transistors 44, 46, 48, 50, 52, and 54 for switching the paths provided on the path part 34, and a USB(universal serial bus) control part 42 which controls the path switching.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic device for connecting peripheral devices such as a keyboard, a mouse, a speaker, a modem and a printer, as well as other electronic devices, and an interface circuit.

[0002]

2. Description of the Related Art In recent years, Universal Serial Bus (USB) has begun to be used as a standard for connecting peripheral devices such as a keyboard, a mouse, a speaker, a modem, and a printer. The USB interface allows an interface that differs for each peripheral device to be easily connected to a host such as a personal computer by the same interface connector.

In the USB interface, there is always one host (a personal computer or the like), and peripheral devices (logical functions are called functions) can be connected to this host to transmit and receive data. With the USB interface, a peripheral device (function) can be further connected to itself by providing a hub.

FIG. 6 shows an example of a connection form between a host 80 and peripheral devices 82 and 92 using a conventional USB interface. The USB interface includes a host interface and a peripheral interface, and peripheral interfaces include a high-speed transfer interface (full speed) and a low-speed transfer interface (low speed).

FIG. 6A shows a configuration in which a host 80 and a peripheral device 82 (full-speed function) for high-speed transfer are connected via a cable 84. A USB circuit (transceiver) 86 is provided in the host 80, and a USB circuit (transceiver) 90 is provided in the peripheral device 82.
Is provided.

[0006] There are two USB data lines (D +, D
−), Pull-down resistors (R1) 88 and 89 are connected to the respective data lines on the host 80 side. On the other hand, on the peripheral device 82 side, the pull-up resistor (R2) 91 is connected to the D + data line because of the full-speed function. According to the USB interface standard, the pull-down resistor (R1) is 15 kΩ ± 5
%, And the pull-up resistance (R2) is 1.5 kΩ ± 5%.

FIG. 6B shows a configuration in which a host 80 and a peripheral device 92 (low-speed function) for performing low-speed transfer are connected via a cable 94. The host 80 is the same as that shown in FIG. 6A. A USB circuit (transceiver) 86 is provided, and pull-down resistors (R1) 88 and 89 are connected to each data line. on the other hand,
On the peripheral device 92 side, since it is a low-speed function, a pull-up resistor (R
2) 95 is connected.

[0008]

As described above, the conventional US
The B interface has a configuration in which pull-down resistors (R1) 88 and 89 are connected to respective data lines on the host 80 side, and a pull-up resistor (R2) 91 is connected to one data line D + in the peripheral device 82 that performs high-speed transfer. The peripheral device 92 that performs low-speed transfer has a configuration (standard) in which the other data line D-pull-up resistor (R2) 95 is connected.

That is, the configuration of the interface circuit differs depending on whether the device is a host or a peripheral device, and whether the peripheral device performs high-speed transfer or low-speed transfer. In a communication system in which devices are connected by a USB interface, a master-slave relationship always exists, and the role of a host and a guest (peripheral device or the like) is determined by the device, and the role is not changed.

However, in recent years, devices that can be both hosts and peripheral devices, for example, portable electronic devices (for example, handheld personal computers (HPCs)) have begun to be widely used.

In general, portable electronic devices (HPCs)
In many cases, a personal computer or the like is used as a host and functions as a guest that directly connects and transmits and receives data. However, when the operation environment is to be improved by connecting a peripheral device such as an extended keyboard to the electronic device (HPC), the electronic device (HPC) functions as a host.

However, the USB interface of an electronic device (HPC) is provided with only one connector for connecting a cable.
If the PC is used as a guest, the configuration is for peripheral devices. In this case, the electronic device (H
PC) can only be used as a guest.

In order to use an electronic device (HPC) as a host, a USB interface for the host must be provided. In this case, the electronic device (HPC) can be used only as a host.

As described above, the conventional USB interface has different configurations for the guest and the host.
The electronic device (HPC) could not function for both the guest and the host.

The present invention has been made in view of the above circumstances, and has as its object to provide an electronic device and an interface circuit that can be used as both a host and a guest.

[0016]

According to the present invention, there is provided an electronic device having an interface circuit for connecting another device, wherein the interface circuit includes a plurality of connectors provided with terminals for connecting data lines. A line driver corresponding to each of the plurality of connectors, for transmitting and receiving a signal via the data line; and a path between the plurality of connectors and the corresponding line driver. Path means provided with a path between terminals of the connector, path switching means for switching a plurality of paths provided in the path means, and control means for controlling path switching by the path switching means. Features.

Thus, a device that functions as a host with respect to the own device is connected to one of the plurality of connectors, and a device that functions as a guest with respect to the own device is connected to another connector, and both are used together. be able to. That is, the own device can function as both a guest and a host. Further, since a path between terminals of different connectors among the plurality of connectors is provided, the own device can be made to function as a relay between other devices.

Also, a first connector for connecting a device functioning as a host to the own device is connected to the plurality of connectors.
And a second connector to which a device functioning as a guest is connected to the own device, a pull-up resistor is connected to a data line connected to a terminal of the first connector, A pull-down resistor is connected to the data line connected to the terminal of the second connector.

[0019] The apparatus further comprises a discriminating means for discriminating a connection state of another device to the plurality of connectors. It is characterized in that the route is switched.

Further, in an interface circuit for connecting another device, a plurality of connectors provided with terminals for connecting data lines are provided, and a plurality of connectors are provided via the data lines respectively corresponding to the plurality of connectors. A path driver provided with a line driver for transmitting and receiving signals, a path between the plurality of connectors and a corresponding line driver, and a path between terminals of different ones of the plurality of connectors; A path switching means provided in the means for switching a plurality of paths, and a control means for controlling path switching by the path switching means are provided.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram illustrating a schematic configuration of an electronic device according to the present embodiment. As shown in FIG. 1, the electronic device according to the present embodiment includes a CPU 1
0, a memory 12, an external storage device 14, a display device 16, an input device 17, and an interface circuit 19. The electronic device shown in FIG. 1 is a device that can be a host or a peripheral device, for example, a portable electronic device (HP
C).

The CPU 10 controls the entire electronic device, and executes various processes according to programs stored in the memory 12. The CPU 10 causes the electronic device to function as, for example, a peripheral device for a personal computer or a host for peripheral devices such as a keyboard, a mouse, a modem, and a printer.

The memory 12 stores programs, data, and the like that define the operation of the CPU 10. External storage device 14
Is composed of a hard disk device, etc.
Stores programs and data.

The display device 16 is constituted by a liquid crystal display or the like, and performs display related to various processes. The input device 17 includes a keyboard, a mouse, and the like, and inputs codes, data, and the like for processing executed by the electronic device.

The interface circuit 19 connects the electronic device to a device functioning as a host (such as a personal computer) or a peripheral device, and basically conforms to the USB (Universal Serial Bus) standard. It was done.

However, in the USB standard, the configuration of the interface circuit is different depending on whether the device is a host or a peripheral device, and whether the peripheral device performs high-speed transfer or low-speed transfer. The interface circuit 19 has a configuration in which both a device functioning as a host and a device functioning as a guest can be simultaneously connected to the own device. The detailed configuration will be described later.

FIG. 2 shows a connection configuration of an electronic device 20 provided with an interface circuit 19 according to the present embodiment, a peripheral device 22 functioning as a guest for the device itself, and a personal computer 24 functioning as a host. An example is shown.

FIG. 2 shows that an electronic device 20 and a peripheral device 22 (either a full-speed function or a low-speed function) are connected via a cable 23, and the electronic device 20 and a personal computer 24 are connected to each other. Are connected via a cable 25.

In this case, the electronic device 20 is
Functions as a host for the personal computer 24 and as a peripheral device for the personal computer 24. The cables 23 and 25 for connecting the electronic device 20 to the peripheral device 22 or the personal computer 24 include two USB data lines (D +, D-) and two power supply power lines (Vcc , GND).

FIG. 3 shows a detailed configuration of the interface circuit 19. As shown in FIG. 3, the interface circuit 19 in the present embodiment is a USB connector (A).
30, a USB connector (B) 32, a path unit 34, a bidirectional line driver (A) 36, a bidirectional line driver (B) 38, a selector 40, and a USB control unit 42 are provided.

The USB connector (A) 30 has a shape conforming to the USB standard, and is a cable 25 for connecting a data line and a power line to a personal computer 24 functioning as a host with respect to its own device. Are combined. The USB connector (A) 30 is provided with terminals D +, D-, Vcc, and GND for each line.
The power supply line terminals Vcc and GND are omitted.

The USB connector (B) 32 has a shape conforming to the USB standard, and has a cable 23 for connecting a data line and a power line to the peripheral device 22 functioning as a guest with respect to the device itself. Are combined. US
The B connector 30 is provided with terminals D + and D- for each line. In addition, the terminals Vcc and GN for the power supply line
D is omitted.

The path section 34 includes a USB connector (A) 30
And a peripheral device 22 connected by a cable 23 connected to a USB connector (B) 32.
And a circuit for switching a data transfer path between the device and the own device. In the present embodiment, the personal computer 2
(A), a data transfer path between the peripheral device 22 and the own device, a route (B), and a data transfer route between the personal computer 24 and the peripheral device 22. Is described as a route (C).

The path unit 34 is output from the USB control unit 42 depending on whether the own device functions as a host, functions as a peripheral device, or relays between the personal computer 24 and the peripheral device 22. The path is switched by the mode signal.

The path section 34 has a USB connector (A) 3
The transistor 44 as a switching element for switching the connection of the data line D + connected to the terminal D +
(Path switching means) is provided, and a transistor 46 (path switching means) is provided as a switching element for switching the connection of the data line D- connected to the terminal D- (connection switching of the path (A)). .

The path section 34 is provided with a transistor 48 (path switching means) as a switching element for switching the connection of the data line D + connected to the terminal D + of the USB connector (B) 32, and a terminal D- A transistor 50 (path switching means) is provided as a switching element for switching the connection of the data line D- connected to the data line D- (connection switching of the path (B)).

The terminal D of the USB connector (A) 30
+ And a transistor 5 as a switching element for switching the connection between the terminal D + of the USB connector (B) 32.
2 (path switching means) is provided, and a transistor 54 (path switching means) is provided as a switching element for switching the connection between the terminal D- of the USB connector (A) 30 and the terminal D- of the USB connector (B) 32. (Connection switching of the route (C)).

The transistors 52 and 54 have a function opposite to that of the transistors 44, 46, 48 and 50, because the mode signal from the USB control unit 42 is input through an inverter. That is, transistors 44, 46, 48, 5
If 0 functions to connect the path, transistors 52 and 54 function to disconnect the path.

A pull-up resistor 56 is connected to the data line D + connected via the transistor 44. That is, the own device is the personal computer 24.
When it functions as a guest, high-speed transfer (full speed) is performed. When performing low-speed transfer (low speed), a pull-up resistor is connected to the data line D- connected via the transistor 46.

A pull-down resistor 58 is connected to the data line D + connected via the transistor 48, and a pull-down resistor 59 is connected to the data line D- connected via the transistor 50. That is, when the own device functions as a host for the peripheral device 22, data is transferred.

The bidirectional line driver (A) 36 is a US
This is a basic component of the B interface, and includes terminals D + and D- of the USB connector (A) 30 and a transistor 4
Data line D whose connection is switched by 4, 46
+, D-, transmission and reception of data and single-end zero (SE0) under the control of the USB control unit 42.
Is detected. The bidirectional line driver (A) 36 includes a differential driver 60, a differential receiver 62, single-ended receivers 64 and 66, and a NOR circuit 68. The differential driver 60, the differential receiver 62, and the single-ended receivers 64 and 66 are connected to the data lines D + and D- of the path (A), respectively.

The differential driver 60 is for data transmission, and is provided through the selector 40.
2 in response to the TxD signal, SE0 signal, and out enable (OE) signal from the data lines D + and D-.

The differential receiver 62 is for data reception, receives data according to the state of the signals on the data lines D + and D-, and outputs the data as an Rcv Data signal to the selector 4.
0 to the USB control unit 42.

The single-ended receivers 64 and 66
The signal state of the data lines D + and D- of the path (A) connected to the terminals D + and D- of the SB connector (A) 30 is held.

The NOR circuit 68 outputs a signal corresponding to the state of the signal held by the single-ended receivers 64 and 66. When the state of the signal on the data lines D + and D- is low level "0", the signal SE0 is output. Detect (S Det1)
“1” is output to the USB control unit 42 as a signal.

The bidirectional line driver (B) 38
This is a basic component of the B interface, and includes terminals D + and D− of a USB connector (B) 32 and a transistor 4
Data line D whose connection is switched by 8, 50
+, D-, transmission and reception of data and single-end zero (SE0) under the control of the USB control unit 42.
Is detected. The bidirectional line driver (B) 38 includes a differential driver 70, a differential receiver 72, single-ended receivers 74 and 76, and a NOR circuit 78. The differential driver 70, the differential receiver 72, and the single-ended receivers 74 and 76 are connected to the data lines D + and D- of the path (B), respectively.

The differential driver 70 is used for data transmission, and is provided via the selector 40.
2 in response to the TxD signal, SE0 signal, and out enable (OE) signal from the data lines D + and D-.

The differential receiver 72 is for data reception, receives data in accordance with the state of the signals on the data lines D + and D-, and outputs the data as an Rcv Data signal to the selector 4.
0 to the USB control unit 42.

The single-ended receivers 74 and 76
The signal state of the data lines D + and D− of the path (B) connected to the terminals D + and D− of the SB connector (B) 32 is held.

The NOR circuit 78 outputs a signal corresponding to the state of the signal held by the single-ended receivers 74 and 76. When the state of the signal on the data lines D + and D- is low level "0", the signal SE0 is output. Detect (S Det2)
“1” is output to the USB control unit 42 as a signal.

The selector 40 is provided between the USB control unit 42 and the bidirectional line driver (A) 36 and the bidirectional line driver (B) 38. The USB control unit 42 supplies a Select signal, a TxD signal, SE0 signal,
An out enable (OE) signal is input. Selector 4
0 is a TxD signal, SE0 according to the Select signal.
Signal, out enable (OE) signal to the bidirectional line driver (A) 36 or the bidirectional line driver (B)
38. That is, the selector 40
Outputs a TxD signal from one of terminals 1A and 1B, an SE0 signal from one of terminals 2A and 2B, and an out enable (OE) signal from one of terminals 3A and 3B.

The selector 40 receives the Rcv Data signals from the differential receivers 62 and 72 of the bidirectional line driver (A) 36 and the bidirectional line driver (B) 38 from the terminals 4A and 4B to control the USB. Output to the unit 42.

The USB control section 42 operates under the control of the CPU 10, and controls the bidirectional line driver (A) 36 or the bidirectional line driver (B) based on the select signal.
Control for selecting any one of the routes 38, the route (A) of the route unit 34
(B) Transistors 44 and 4 for switching (C)
6, 48, 50, 52, 54, switching control by the mode signal, data transmission / reception to / from the bidirectional line driver (A) 36 and the bidirectional line driver (B) 38,
Single-ended zero (SE0) detection (S Det1,
S Det2).

Normally, in the USB interface, a single end zero (SE0) is set to an end of packet (EO).
P), reset, and disconnection detection of the line. In the present embodiment, the USB connector (A) 30 or the US
B connector (B) 32 (and cables 23 and 25)
It is also used to determine the connection status of devices via the.

Next, the operation of connecting the electronic device 20 to another device via the interface circuit 19 in this embodiment will be described. FIG. 4 is a flowchart showing the path switching operation by the USB control unit 42.

The electronic device 20 includes the interface circuit 1
The USB connector (A) 30 is connected to a cable 25 and a personal computer 24 is connected as a host, or the USB connector (B) 32 is connected to a cable 23 and a peripheral device 22 (for example, a keyboard) is connected. Or both are connected.

The USB control unit 42 is set as an initial state.
The mode signal output from is off, and the path (A)
And the path (B) are connected. Cable 25 (personal computer 2)
4) When the cable 23 (peripheral device 22) is connected, the signals via the two data lines D + and D- terminated on the personal computer 24 side and the peripheral device 22 side correspond to both the corresponding signals. SE0 Detect (S Det1) signal, SE0 De via the bidirectional line driver (A) 36 and bidirectional line driver (B) 38
The tect (S Det2) signal is input to the USB control unit 42.

The USB control unit 42 of the electronic device 20 outputs the SE0 Detect (S Det1) signal, SE0 Detect
From the (S Det2) signal, it is possible to know the connection status of the other device to the own device.

When the connection of the cables to the USB connector (A) 30 and the USB connector (B) 32 is not detected (step S1), the USB control unit 42 executes another process that does not require the path switching (step S1). S2).

On the other hand, the USB connector (A) 30
When the connection of the cable to the B connector (B) 32 is detected (step S3), the USB control unit 42
The signal is turned on (step S4). Thus, the path (A) is formed by the transistors 44 and 46 so that the transistor 4
The path (B) is invalidated by 8, 50, and the path (C) is activated by the transistors 52, 54.

In this case, the personal computer 24 and the peripheral device 22 connect the interface circuit 19 of the electronic device 20 (USB connector (A) 30, transistor 52,
54, via the USB connector (B) 32). That is, the electronic device 20 performs a function of only relaying between the personal computer 24 and the peripheral device 22. Also, the personal computer 24
The peripheral device 22 can function as a guest.

If the connection of the cable 25 to the USB connector (A) 30 is detected (step S5), U
The SB control unit 42 uses the Select signal to
For 0, the bidirectional line driver (A) 36 is selected, and the mode signal is turned off (step S6). As a result, the path (A) is enabled by the transistors 44 and 46, and data communication conforming to the standard of the general USB interface is performed.

In this case, the electronic device 20 functions as a guest for the personal computer 24. When transmitting data from the electronic device 20, the USB control unit 42
Is output from the terminal 1A of the selector 40.
Driver 6 of the bidirectional line driver (A) 36 from
0, and further to the personal computer 24 via the path (A) and the USB connector (A) 30. The data signal from the personal computer 24 is received by the differential receiver 62 via the path (A), output to the terminal 4A of the selector 40, and further output to the USB control unit 42 as an Rcv Data signal.

When the connection of the cable 23 to the USB connector (B) 32 is detected (step S7), U
The SB control unit 42 uses the Select signal to
For 0, the bidirectional line driver (B) 38 is selected, and the mode signal is turned off (step S8). As a result, the path (B) is made effective by the transistors 48 and 50, and data communication conforming to the general USB interface standard is performed.

In this case, the electronic device 20 is
Act as a host for When data transmission is performed from the electronic device 20, the signal TxD output from the USB control unit 42 is output from the terminal 1B of the selector 40 to the differential driver 70 of the bidirectional line driver (B) 38,
The signal is further output to the peripheral device 22 via the path (B) and the USB connector (B) 32. Further, a data signal from the peripheral device 22 is received by the differential receiver 72 via the path (B) and output to the terminal 4B of the selector 40,
Further, it is output to the USB control unit 42 as an Rcv Data signal.

As described above, the interface circuit 19 provided in the electronic device 20 is provided with the two USB connectors (A) 30 and the USB connectors (B) 32, and furthermore, the corresponding paths (A) ( B), bidirectional line driver (A) 36, bidirectional line driver (B) 3
Since the electronic device 20 is provided, the personal computer 24 functioning as a host and the peripheral device 22 functioning as a guest can be arbitrarily connected to the electronic device 20 to form a communication system.

Further, the electronic device 20 can be made to function to relay between the personal computer 24 and the peripheral device 22. Therefore, in the connection form shown in FIG. 2, even when the peripheral device 22 functions as a guest of the personal computer 24, there is no need to change the connection of the cable.

In the above description, the personal computer 24 is connected to the USB connector (A) 30,
When the peripheral device 22 is connected to the USB connector (B) 32, the path (C) is enabled to connect the personal computer 24 and the peripheral device 22, and the electronic device 20 is used for relay. However, the user can arbitrarily select from three types of connection forms.

That is, when the personal computer 24, the peripheral device 22, and the electronic device 20 are connected, the connection forms are the personal computer 24 and the electronic device 20, the electronic device 20, the peripheral device 22, and the personal computer 24. And the peripheral device 22. The user inputs an instruction to select one of the three types of connection from the input device 17 such as a keyboard (or a mechanical switch or the like). The USB control unit 42 outputs a Select signal and a mode signal in response to an instruction from the user so that the operation according to the specified connection mode is enabled.

In the above-described embodiment, the switches for switching the path in the path section 34 are constituted by the transistors 44, 46, 48, 50, 52 and 54. However, the switches may be constituted by FETs. Furthermore, it can be configured using mechanical switching parts such as a toggle switch.

Although only one connector is provided from the electronic device 20 (HPC) to the peripheral device 22, a circuit may be formed using a plurality of connectors and a bidirectional line driver.

[0072]

As described above in detail, according to the present invention, in an electronic device having an interface circuit for connecting another device, the interface circuit has a plurality of terminals provided with terminals for connecting data lines. Connectors and
A line driver that transmits and receives signals via data lines corresponding to each of the plurality of connectors, a path between the plurality of connectors and the corresponding line driver, and a terminal between different ones of the plurality of connectors. By having a path section provided with a path, a circuit for switching a plurality of paths provided in the path section, and a control function for controlling path switching by this circuit, one of a plurality of connectors can be connected to its own device. Connect a device that functions as a host to
A device that functions as a guest can be connected to the own device to another connector, and both can be used together, and the own device can function as both a guest and a host. Further, since a path between terminals of different connectors among the plurality of connectors is provided, the own device can be made to function as a relay between other devices.

[Brief description of the drawings]

FIG. 1 is an exemplary block diagram showing a schematic configuration of an electronic apparatus according to an embodiment of the invention.

FIG. 2 is a diagram showing an example of a connection form between a peripheral device 22 and a personal computer 24 via an interface circuit 19 in the embodiment.

FIG. 3 is a diagram showing a detailed configuration of an interface circuit 19;

FIG. 4 is an interface circuit 1 by a USB control unit 42;
9 is a flowchart showing a path switching operation when data transfer is performed via the communication path 9;

FIG. 5 shows a host 80 using a conventional USB interface.
FIG. 4 is a diagram showing an example of a connection form between a device and a peripheral device 82;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... CPU 12 ... Memory 14 ... External storage device 16 ... Display device 17 ... Input device 19 ... Interface circuit 20 ... Electronic device 22 ... Peripheral device 24 ... Personal computer 30 ... USB connector (A) 32 ... USB connector (B) 34 ... Path section 36. Bidirectional line driver (A) 38. Bidirectional line driver (B) 40. Selector 42. USB control section 56. Pull-up resistors 58 and 59. Pull-down resistors 60 and 70. Differential drivers 62 and 72. … Differential receiver

Claims (4)

[Claims] 1. An electronic device having an interface circuit for connecting another device, wherein the interface circuit includes: a plurality of connectors provided with terminals for connecting data lines; A corresponding line driver for transmitting / receiving a signal via the data line, a path between the plurality of connectors and the corresponding line driver, and a path between terminals of different ones of the plurality of connectors. An electronic apparatus comprising: a path unit provided; a path switching unit that switches a plurality of paths provided in the path unit; and a control unit that controls path switching by the path switching unit. 2. A plurality of connectors, a first connector for connecting a device functioning as a host to the own device, and a second connector for connecting a device functioning as a guest to the own device. A connector is provided, a pull-up resistor is connected to a data line connected to a terminal of the first connector, and a pull-down resistor is connected to a data line connected to a terminal of the second connector. The electronic device according to claim 1, wherein: 3. A control device, comprising: a determination unit configured to determine a connection state of another device to the plurality of connectors; and a control unit configured to determine a connection state of the plurality of connectors in accordance with a determination result by the determination unit. 2. The electronic device according to claim 1, wherein a path is switched. 4. An interface circuit for connecting another device, comprising: a plurality of connectors provided with terminals for connecting data lines; and a plurality of connectors via the data lines corresponding to the plurality of connectors. A path driver provided with a line driver for transmitting and receiving signals; a path between the plurality of connectors and a corresponding line driver; and a path between terminals of different ones of the plurality of connectors; An interface circuit comprising: a path switching unit provided in the unit for switching a plurality of paths; and a control unit for controlling path switching by the path switching unit.