U.S. patent application number 13/252514 was filed with the patent office on 2012-02-02 for electronic device.
This patent application is currently assigned to NIKON CORPORATION. Invention is credited to Takeshi KAWANO.
Application Number | 20120030485 13/252514 |
Document ID | / |
Family ID | 39541869 |
Filed Date | 2012-02-02 |
United States Patent
Application |
20120030485 |
Kind Code |
A1 |
KAWANO; Takeshi |
February 2, 2012 |
ELECTRONIC DEVICE
Abstract
A USB electronic device with a power source loaded therein,
which is connected to another USB electronic device via a USB
connector, comprises a voltage detection unit that detects a
voltage at an identification pin of the USB connector, a power
supply control unit that controls connection/disconnection between
a power supply pin of the USB connector and the power source based
upon a change in voltage at the identification pin detected by the
voltage detection unit and an allow/disallow control unit that
executes control to allow/disallow detection of the voltage change
at the identification pin.
Inventors: |
KAWANO; Takeshi; (Koto-ku,
JP) |
Assignee: |
NIKON CORPORATION
Tokyo
JP
|
Family ID: |
39541869 |
Appl. No.: |
13/252514 |
Filed: |
October 4, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12000762 |
Dec 17, 2007 |
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13252514 |
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Current U.S.
Class: |
713/300 |
Current CPC
Class: |
G06F 1/266 20130101;
G06F 2213/0042 20130101 |
Class at
Publication: |
713/300 |
International
Class: |
G06F 1/26 20060101
G06F001/26; G06F 13/00 20060101 G06F013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 25, 2006 |
JP |
2006-347361 |
Claims
1. A USB electronic device with a power source loaded therein,
which is connected to another USB electronic device via a USB
connector, comprising: a voltage detection unit that detects a
voltage at an identification pin of the USB connector; a power
supply control unit that controls connection/disconnection between
a power supply pin of the USB connector and the power source based
upon a change in voltage at the identification pin detected by the
voltage detection unit; and an allow/disallow control unit that
executes control to allow/disallow detection of the voltage change
at the identification pin.
Description
[0001] The disclosure of the following priority application is
herein incorporated by reference: Japanese Patent Application No.
2006-347361 filed Dec. 25, 2006.
[0002] This is a Continuation of application Ser. No. 12/000,762
filed Dec. 17, 2007. The disclosure of the prior application is
hereby incorporated by reference herein in its entirety.
BACKGROUND
[0003] 1. Field of the Invention
[0004] The present invention relates to an electronic device
connected through a USB (universal serial bus) interface.
[0005] 2. Description of Related Art
[0006] The USB is known widely as an interface through which a
personal computer and its peripheral devices are connected. A USB
host equipped with a USB host controller and a USB device equipped
with a USB device controller are typically connected through the
USB interface. When the USB host and the USB device are connected
with each other via the USB connection, power is normally supplied
from the USB host to the USB device. However, there are
technologies known in the related art that allow power to be
supplied from the USB device to the USB host, as well (see, for
instance, Japanese Laid Open Patent Publication No.
2005-25405).
SUMMARY
[0007] The USB device supplies power to the USB host in the related
art by supplying power to a VBUS pin as the USB host becomes
connected thereto lowering the voltage at an ID pin to a
predetermined level. This gives rise to a concern that the USB
device may supply power to a USB host connected thereto even if the
USB host does not require power as the voltage at the ID pin
becomes lowered to the predetermined level.
[0008] According to the first aspect of the present invention, a
USB electronic device with a power source loaded therein, which is
connected to another USB electronic device via a USB connector. The
USB electronic device comprises voltage detection unit that detects
a voltage at an identification pin of the USB connector, a power
supply control unit that controls connection/disconnection between
a power supply pin of the USB connector and the power source based
upon a change in voltage at the identification pin detected by the
voltage detection unit, and an allow/disallow control unit that
executes control to allow/disallow detection of the voltage change
at the identification pin.
[0009] The allow/disallow control unit includes a pull-up circuit
and a switch that connects/disconnects the pull-up circuit to/from
the identification pin, and the power supply control unit connects
the pull-up circuit to the identification pin when the detection of
the voltage change is allowed and disconnects the pull-up circuit
from the identification pin when detection of the voltage change is
disallowed by controlling changeover at the switch.
[0010] It is preferred that the USB electronic device comprises a
setting operation unit with which a user selects a setting to
allow/disallow the detection of a voltage change at the
identification pin.
[0011] According to the second aspect of the present invention, a
USB electronic device with a power source loaded therein, which is
connected to another USB electronic device via a USB connector. The
USB electronic device comprises a voltage detection unit that
detects a voltage at an identification pin of the USB connector and
power supply control unit that controls connection/disconnection
between a power supply pin of the USB connector and the power
source based upon a voltage change at the identification pin
detected by the voltage detection unit. The power supply control
unit includes a first switch disposed between the power supply pin
and the power source, with which the power supply pin and the power
source are connected with each other or disconnected from each
other in response to a switching control signal and a second switch
with which allow/disallow control is executed with regard to
changeover at the first switch.
[0012] In the USB electronic device according to the second aspect
of the present invention, when the changeover at the first switch
is allowed via the second switch, the switching control signal is
applied to the first switch via the second switch, whereas when the
changeover at the first switch is disallowed via the second switch,
the switching control signal is interrupted from the first switch
by the second switch.
[0013] In the USB electronic device according to the second aspect
of the present invention, the second switch is disposed between a
switching control terminal of the first switch and the
identification pin of the USB connector so as to connect/disconnect
the switching control terminal of the first switch to/from the
identification pin of the USB connector. The first switch is a
semiconductor switching element and the switching control signal is
applied to a switching control terminal of the semiconductor
switching element, which is turned ON/OFF in correspondence to a
voltage level at the identification pin. When the voltage level at
the identification pin is low, the semiconductor switching element
enters an ON state connecting the power supply pin to the power
source.
[0014] It is preferred that the electronic device according to the
second aspect of the present invention comprises an allow/disallow
control unit that executes control to allow/disallow detection of a
voltage change at the identification pin. In this case, the
allow/disallow control unit is able to consists as well as an
allow/disallow control unit comprised in a USB electronic device
according to the first aspect of the present invention.
[0015] According to the third aspect of the present invention, a
USB electronic device that includes a USB device controller and a
power source loaded therein. The USB electronic device comprises a
USB connector at which an electronic device equipped with a USB
host controller is connected, a voltage detection unit that detects
a voltage at an identification pin of the USB connector, a first
switch that connects/disconnects a power supply pin of the USB
connector to/from the power source, a detection unit that detects a
voltage change at the identification pin detected via the voltage
detection unit, a second switch disposed between a switching
control terminal of the first switch and the identification pin, an
allow/disallow control unit that executes control to allow/disallow
detection of a voltage change by the detection unit, and a
switching control unit that executes switching control for the
second switch so as to connect the identification pin to the
switching control terminal of the first switch when the detection
of the voltage change by the detection unit is allowed by the
allow/disallow control unit and the voltage change is detected by
the detection unit.
[0016] The USB electronic device according to the third aspect of
the present invention is still able to comprise a setting operation
unit with which a user selects a setting to allow/disallow the
detection of a voltage change at the identification pin. The
allow/disallow control unit in the USB electronic device according
to the third aspect of the present invention includes a pull-up
circuit and a switch that connects/disconnects the pull-up circuit
to/from an identification pin and the switch connects the pull-up
circuit to the identification pin when a setting for allowing
detection of a voltage change is selected via the setting operation
unit and disconnects the pull-up circuit from the identification
pin when detection of the voltage change is disallowed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 illustrates the interface system achieved in an
embodiment of the present invention; and
[0018] FIG. 2 illustrates how a USB host adopting a structure
different from that of the USB host in FIG. 1 may be connected.
DETAILED DESCRIPTION OF EMBODIMENTS
[0019] The following is an explanation of the best embodiment of
the invention given in reference to the drawings.
First Embodiment
[0020] FIG. 1 illustrates the interface system achieved in the
first embodiment of the present invention. The interface system
shown in FIG. 1 is constituted with a plurality of electronic
devices connected with each other through a USB connection. The USB
connection is achieved in compliance with the USB (universal serial
bus) specification which is set forth by the USB Implementers Forum
(USB-IF) A USB device 10 and a USB host 50 in the interface system
achieved in the embodiment are directly connected with each other
through a connector RC 11 and a connector PL 2 without a cable,
with power supplied from the USB device 10 to the USB host 50. It
is to be noted that in the description of the embodiment, the
connector RC 11 and the connector PL 2 may be otherwise referred to
as USB connectors.
[0021] The USB device 10 may be, for instance, an electronic
camera, whereas the USB host 50 may be a wireless LAN module. By
directly connecting the wireless LAN module 50 to the electronic
camera 10 via the USB connectors, image data accumulated in the
electronic camera 10 can be directly transferred to a server or the
like on a network without having to transmit the image data via a
personal computer or the like.
[0022] The USB interface comprises a power source VBUS line, a data
D+ line, a data D- line, a reference potential GND line and an ID
line. The ID line is used to identify a dual-role device as a "USB
host" or a "USB device". A dual role device is a device that
operates in compliance with the USB-OTG specification (On-The-Go
Supplement to the USB 2.0 Specification) and may be determined to
be operating as a "USB host" or as a "USB device" depending upon
the voltage level detected at the ID line.
[0023] The power supply between devices connected through a USB
connection is executed through the VBUS line. In addition, the
devices connected through the USB connection communicate with each
other through serial communication via a pair of data lines, i.e.
the D+ line and the D- line.
[0024] The USB device 10 in FIG. 1 includes a control unit 12, a
device controller 13, a semiconductor switching element (hereafter
referred to as an FET) 14 such as a field effect transistor,
resistors 15 and 20, diodes 16 and 19, analog switches 17 and 18
and the connector RC 11 mentioned earlier, with a battery 11 loaded
therein. It is to be noted that no explanation of members including
the members engaged in photographing processing in the camera, such
as an imaging optical system, an imaging sensor, a image processing
unit, a memory, a operation member, a recording medium and the like
of the USB device 10 is provided in this specification.
[0025] Power is supplied from the battery 11 to the various
components and elements constituting the USB device 10, such as the
control unit 12 and the device controller 13. The control unit 12
includes a microcomputer and controls the operations of the various
components and elements in the USB device 10 (an electronic camera
in this example). In response to an instruction from the control
unit 12, the device controller 13 executes control so as to enable
the USB device 10 to operate as the "USB device". Data
communication between the USB device 10 and the USB host 50 is
controlled by a host controller 51 to be detailed later. The USB
interface is configured so that the USB device 10 cannot transmit
data to the USB host 50 unless the USB host 50 grants a bus
utilization authorization to the USB device 10.
[0026] The analog switch 18 is disposed between a gate terminal of
the FET 14 and an identification pin ID of the connector RC 11 and
its ON/OFF state is controlled based upon a switching control
signal provided by the control unit 12. More specifically, the
analog switch 18 enters an ON state when the logic level of the
switching control signal is at H and enters an OFF state when the
logic level of the switching control signal is at L.
[0027] The ON/OFF state of the FET 14 is controlled based upon the
state selected for the analog switch 18 and the voltage level at
the ID line. In more specific terms, the FET 14 enters an ON state
when the analog switch 18 is in the ON state and the voltage at the
ID line is equal to or less than a predetermined voltage level. If
the analog switch 18 is in the OFF state, the FET 14 assumes the
OFF state as well. In addition, even if the analog switch 18 is in
the ON state, the FET 14 assumes the OFF state if the voltage at
the ID line is higher than the predetermined voltage level. As the
FET 14 enters the ON state, the battery 11 becomes connected to a
VBUS pin of the connector RC 11 via the FET 14 and the diodes 16.
The diode 16 is disposed for purposes of reverse current
prevention, whereas the resistor 15 is disposed to set the
potential at the gate terminal of the FET 14 to a predetermined
potential level.
[0028] It is to be noted that another type of switching element
such as an analog switch or a relay may be used in place of the FET
14.
[0029] The ON/OFF state of the analog switch 17 is controlled based
upon a switching control signal provided by the control unit 12.
More specifically, the analog switch 17 enters an ON state when the
logic level of the switching control signal is at H and enters an
OFF state when the logic level of the switching control signal is
at L.
[0030] The user of the USB device 10 selects a setting allowing the
use of a wireless LAN module through, for instance, a menu
operation performed by using the operation member. The control unit
12 at the USB device 10 turns on the analog switch 17 as the
wireless LAN module use setting is selected, but the control unit
12 sustains the analog switch 17 in the OFF state until the
wireless LAN module use setting is selected.
[0031] The control unit 12 includes a detection port P.sub.ID used
to detect the voltage level at the ID line. As the analog switch 17
is turned on, the ID line becomes connected with the positive pole
of the battery 11 via the resistor 20, and thus becomes pulled up.
Namely, when the connector RC 11 is in an open state, the level of
the voltage at the ID line indicates a voltage value higher than a
predetermined voltage. Thus, when the wireless LAN module use
setting is selected, the voltage at the ID line shifts from high
level to low level as another device becomes connected to the USB
device 10 via the connector RC 11 and the ID line becomes connected
with the GND line via the other device, enabling the control unit
12 to detect the connection with the other device by reading the
signal of the change in voltage at the detection port P.sub.ID.
[0032] When the wireless LAN module use setting is not selected,
the analog switch 17 does not enter the ON state and thus, the ID
line does not become connected to the battery 11 via the resistor
20 leaving the level of the voltage at the ID line in an
indeterminate state while the connector RC 11 is in the open state.
Under these circumstances, even if another device becomes connected
to the USB device 10 via the connector RC 11 and the ID line
becomes connected to the GND line via the other device, the control
unit 12 is not able to detect a reduction in the voltage level at
the ID line. It is to be noted that the diode 19 is disposed for
purposes of preventing a reverse flow of current at the ID
line.
[0033] The connector RC 11 is a Mini B-type receptacle (Mini-B
receptacle). The Mini B-type receptacle is a connector dedicated to
the "USB device". A Mini B-type plug (Mini-B plug) at the "USB
host" or a "USB cable" can be plugged into the connector RC 11. In
the embodiment, the Mini B-type plug (Mini-B plug) at the USB host
50 is connected to the connector RC 11. The connector RC 11
includes a VBUS pin corresponding to the VBUS line, a D+ pin
corresponding to the D+ line, a D- pin corresponding to the D-
line, a GND pin corresponding to the GND line and an ID pin
corresponding to the ID line.
[0034] The USB host 50 includes a control unit 52, the host
controller 51 and the connector PL 21. It is to be noted that the
figure does not include an illustration of the components and
elements engaged in wireless communication processing in the USB
host 50. The USB host 50 does not have a power source and instead,
it receives power supplied from the USB device 10 and delivers it
to the host controller 51 and the control unit 52.
[0035] The control unit 52 includes a microcomputer and controls
the operations of the various components and elements in the USB
host 50 (a wireless LAN module in this example). In response to an
instruction from the control unit 52, the host controller 51
executes control so as to enable the USB host 50 to operate as the
"USB host". Any processing via the bus is invariably triggered by
the USB host 50 under control executed by the host controller
51.
[0036] The connector PL 21 is a Mini B-type plug (Mini-B plug). The
A Mini B-type plug is a connector dedicated to the "USB host". The
Mini B-type receptacle (Mini-B receptacle) at the "USB device"
i.e., the connector RC 11, is connected to the connector PL 21. The
connector PL 21 includes a VBUS pin corresponding to the VBUS line,
a D+ pin corresponding to the D+ line, a D- pin corresponding to
the D- line, a GND pin corresponding to the GND line and an ID pin
corresponding to the ID line. It is to be noted that the GND pin
and the ID pin are connected with each other within the USB host
50.
[0037] Power is supplied from the USB device 10 to the USB host 50
through the following procedure.
[0038] First, the USB device 10 and the USB host 50 become
connected with each other via the connector RC 11 and the connector
PL 21. The wireless LAN module use setting is selected at the USB
device 10 through a menu operation performed by using, for
instance, the operation member. Once the use of the wireless LAN
module is allowed, the control unit 12 at the USB device 10 sets
the logic level of the switching control signal output to the
analog switch 17 to H, thereby turning on the analog switch 17. As
the analog switch 17 is turned on, the detection port P.sub.ID of
the control unit 12 becomes connected to the power source via the
resistor 20 and thus becomes pulled up. As a result, the control
unit 12 becomes able (is allowed) to detect the reduction in the
voltage level at the ID line.
[0039] In the wireless LAN module use allowed state achieved as
described above, the control unit 12 of the USB device 10 switches
the logic level of the switching control signal output to the
analog switch 18 to H, thereby turning on the analog switch 18, as
the control unit 12 detects a reduction in the voltage at the
detection port P.sub.ID, i.e., a reduction in the voltage level at
the ID line. As the analog switch 18 is turned on, the ID line
where the voltage level has become lower is connected to the gate
terminal of the FET 14, thereby turning on the FET 14, which, in
turn, allows the power from the battery 11 to be supplied from the
USB device 10 to the USB host 50 through the VBUS line.
[0040] When the use of the wireless LAN module is not allowed, the
control unit 12 of the USB device 10 switches the logic level of
the switching control signal output to the analog switch 17 to L,
thereby turning off the analog switch 17. In addition, when the
control unit 12 does not detect a reduction in the voltage at the
ID line, it switches the logic level of the switching control
signal output to the analog switch 18 to L, thereby turning off the
analog switch 18.
[0041] The following advantages are achieved in the interface
system in the embodiment described above.
[0042] (1) The interface system in the first embodiment is
configured so that while the USB device 10 and the USB host 50 are
connected with each other via the USB connectors, power can be
supplied from the USB device 10 to the USB host 50 through the VBUS
line in correspondence to the voltage detected at the ID line. The
USB device 10 includes the analog switch 17 through which detection
of a change in voltage level at the ID line by the control unit 12
is allowed or disallowed. Thus, as long as the detection of voltage
level change at the ID line is disallowed, a USB device 10 adopting
the failsafe structure does not detect a voltage reduction even
when an unexpected device becomes connected to the USB device 10
and the voltage at the ID line becomes lower.
[0043] (2) When the analog switch 17 is in the ON state, the ID
line is connected through a pull-up connection to the power source
(battery 11) via the resistor 20. When the analog switch 17 is in
the OFF state, however, the ID line is not connected to the power
source through the pull-up connection. Consequently, when the
detection is not allowed, the ID line, at which the voltage level
is neither H level nor L level, can be set to a high impedance
state.
[0044] (3) In addition, the USB device 10 in the interface system
achieved in the first embodiment includes the FET 14 through which
the power line connecting the power source (battery 11) with the
VBUS line is turned ON/OFF and the analog switch 18 through which
an ON/OFF changeover at the FET 14 is allowed/disallowed. As a
result, as long as the changeover is disallowed, the USB device
adopting the failsafe structure does not allow the FET 14 to enter
the ON state even if the voltage at the ID line becomes lower.
[0045] (4) The switching control signal for the FET 14 is input to
the gate terminal of the FET 14 when the analog switch 18 is in the
ON state but the switching control signal is not input when the
analog switch 18 is in the OFF state. As a result, as long as the
changeover at the FET 14 is disallowed, the FET 14 is never turned
on and thus, the power supply via the VBUS line is disabled with a
high level of reliability regardless of what type of switching
control signal is generated.
[0046] (5) The analog switch 18 is switched on only after the
analog switch 17 first enters the ON state and thus, the FET 14
never enters the ON state unless a voltage reduction is detected at
the ID line.
[0047] (6) When the analog switch 18 is in the OFF state, the FET
14, too, invariably assumes the OFF state. Namely, the FET 14 is a
P-type FET which enters the ON state as the gate terminal becomes
grounded. Consequently, whenever power should not be supplied from
the USB device 10 to the USB host 50, the power supply can be
reliably stopped.
[0048] (7) Power can be supplied from the USB device 10 to the USB
host 50 without having to constitute the USB device 10 as a dual
role device, i.e., without having to install a controller or
software in compliance with the USB-OTG specification in the USB
device. As a result, an inexpensive interface system is
realized.
Second Embodiment
[0049] FIG. 2 illustrates the interface system achieved in the
second embodiment of the present invention with a USB host 60
different from that shown in FIG. 1 connected therein. The USB
device 10 and the USB host 60 in FIG. 2 are connected with each
other via a USB cable 65. As in the first embodiment, the USB
device 10 may be constituted with an electronic camera and the USB
host 60 may be constituted with a wireless LAN module in the
example presented in FIG. 2. The USB host 60 in the second
embodiment has a function of supplying power to the USB device
10.
[0050] Since the USB device 10 is similar to that shown in FIG. 1,
its explanation is omitted. It is to be noted that FIG. 2 does not
provide an illustration of the individual components, elements and
the like engaged in the photographing processing executed in the
camera. The USB cable 65 is a directional cable. A connector PL 42
disposed at one end of the USB cable 65 is a Mini-B type plug
(Mini-B plug). The Mini-B plug is a connector used to the "USB
device". The RC connector RC 11 of the "USB device", i.e., the
Mini-B type receptacle (Mini-B receptacle) is connected to the
connector PL 42.
[0051] A connector PL 41, disposed at the other end of the USB
cable 65, is an A-type plug (A plug). The A-type plug is a
connector to the "USB host". A connector RC 31 of the "USB host",
i.e., an A-type receptacle (A receptacle) is connected to the
connector PL 41. Since the connectors disposed at the two ends of
the USB cable 65 assume different shapes, two "USB hosts" or two
"USB devices" are never connected with each other by mistake.
[0052] The connector PL 41 is a full-size connector with four pins.
The connector PL 42 is a Mini-type connector as explained earlier
and includes five pins. Since the connector PL 41 does not include
an ID pin, the USB cable 65 does not include a wiring for ID pin
connection and the ID pin of the connector PL 42 is left
open-circuited.
[0053] The USB host 60 includes a control unit 62, a host
controller 61 and the connector RC 31 (A-type receptacle), with a
battery 63 loaded therein. It is to be noted that an illustration
of the components, elements and the like in the USB host 60 engaged
in wireless communication processing is not provided. The USB host
60 supplies power from the battery 63 to the host controller 61 and
the control unit 62.
[0054] The control unit 62 includes a microcomputer and controls
the operations of the individual components, elements and the like
in the USB host 60. In response to an instruction from the control
unit 62, the host controller 61 executes control so as to enable
the USB host 60 to operate as the "USB host". Any processing via
the bus is invariably triggered by the USB host 60 under control
executed by the host controller 61.
[0055] The connector RC 31 is an A-type receptacle (A-receptacle).
The A-receptacle is a connector dedicated to the "USB host". The
connector PL 41 (A plug) of the USB cable 65 is connected to the
connector RC 31. The connector RC 31 includes a VBUS pin
corresponding to the VBUS line, a D+ pin corresponding to the D+
line, a D- pin corresponding to the D- line and a GND pin
corresponding to the GND line.
[0056] The USB device 10 constituting the interface system shown in
FIG. 2 is able to engage in operation on the power provided therein
(from the battery 11) without having to rely on power supplied from
the "USB host" via the VBUS line.
[0057] The operational procedure adopted in the interface system
achieved in the second embodiment is now explained.
[0058] As in the first embodiment, the wireless LAN module 60
becomes connected to the USB device 10 via the USB cable 65. From
the menu screen at the USB device 10, the wireless LAN module use
setting or the wireless LAN module nonuse setting is selected. At
the USB device 10, the wireless LAN module nonuse setting is
selected as the default setting. When the wireless LAN module
nonuse setting is selected, the control unit 12 sets the analog
switch 17 in the OFF state and thus, the FET 14 remains off with no
power from the battery 11 in the USB device 10 supplied to the
VBUS. As a result, even when the wireless LAN module 60 with the
battery 63 loaded therein is connected with the USB device 10,
i.e., even when the battery 63 is connected to the VBUS pin of the
connector RC 11 of the USB device 10, power source interference
between the batteries 11 and 63 does not occur.
[0059] As the wireless LAN module use setting is selected in the
menu screen, the analog switch 17 is turned on pulling up the
detection port P.sub.ID and enabling the control unit 12 to detect
a voltage change at the voltage detection port P.sub.ID. In the
interface system achieved in the second embodiment, the other end
of the ID line at the USB cable 65 is open-circuited and the
voltage at the voltage detection port P.sub.ID in the control unit
12 remains unchanged regardless of whether the USB host 60 is
connected or disconnected. Consequently, the FET 14 sustains the
OFF state, preventing the power source interference between the
batteries 11 and 63.
[0060] (Variation 1)
[0061] One of or both of the analog switches 17 and 18 may be
constituted with a mechanical switch. In such a case, the
mechanical switch is turned on when the user allows to use the
wireless LAN module with the USB device 10. If, on the other hand,
the user disallows use of the wireless LAN module with the USB
device 10, the mechanical switch is turned off.
[0062] (Variation 2)
[0063] Instead of using a signal input from the outside of the USB
device 10 through the ID pin as the switching control signal to be
input to the gate terminal of the FET 14, the switching control
signal may be generated in the control unit 12. In such a case,
upon detecting a reduction in the voltage level at the ID line
applied from the outside of the USB device 10, the control unit 12
outputs a signal of L level as the switching control signal to be
input to the gate terminal of the FET 14. In addition, if a
reduction in the voltage level at the ID line is not detected, the
control unit 12 outputs a signal of H level as the switching
control signal for the FET 14.
[0064] (Variation 3)
[0065] While an explanation is given above on an example in which
the USB device includes both the switch 17 and the switch 18, the
USB device may instead include either of the switches 17 or 18.
[0066] (Variation 4)
[0067] In the interface system achieved in the first embodiment,
power is supplied from the USB device 10 with the battery 11 loaded
therein to the USB host 50 into which a battery cannot be loaded.
However, the present invention may instead be adopted in an
interface system in which power is supplied from a USB host with a
battery loaded therein to a USB device into which a battery cannot
be loaded. In the latter case, the interface system should adopt a
structure that allows power to be supplied through the VBUS line
from the USB host to the USB device in correspondence to the
voltage at the ID line.
[0068] While an explanation is given above on an example in which
the USB device 10 is constituted with an electronic camera, the
present invention is not limited to this example and it may be
adopted in conjunction with a USB device constituted with a
portable electronic device such as a portable telephone or a
PDA.
[0069] While the USB host 50 in the description provided above is a
wireless LAN module, the present invention may be adopted in
conjunction with a USB host constituted with a tuner module, a GPS
receiver module or the like, instead.
[0070] The above described embodiments are examples, and various
modifications can be made without departing from the scope of the
invention.
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