Communications: electrical – Systems – With specific power supply
Reexamination Certificate
1999-10-25
2001-03-06
Wu, Daniel J. (Department: 2736)
Communications: electrical
Systems
With specific power supply
C340S693100, C710S100000, C713S300000
Reexamination Certificate
active
06198384
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an interface circuit, and more particularly, to the control system power supplied to an interface circuit which performs data transmission between devices.
Interfaces are used to transmit data between personal computers and peripheral equipment, such as audio and video equipment or digital cameras. The interfaces of connected apparatuses are connected to one another by cables that include power lines and data lines. There is a type of interface that supplies power from one apparatus to another apparatus via the personal computer regardless of whether the system power of the personal computer is off. Among such interfaces, the IEEE1394 standard interface has attracted much attention.
FIG. 1
is a block diagram showing a data transmission device
100
, which is provided with an interface. The data transmission device
100
is incorporated in a personal computer. Further, the data transmission device
100
includes two connectors
51
,
52
, a host controller
54
, and an interface circuit
59
, which has an interface (I/F) controller
55
, two regulators
56
,
57
, and a diode
58
. A system power circuit
53
is also incorporated in the personal computer.
The first connector
51
is connected to a first peripheral apparatus (not shown, in this case, a digital camera) via a first cable
61
. The second connector
52
is connected to a second apparatus (not shown, in this case, a color page printer) via a second cable
62
. Each cable
61
,
62
is a six line cable having a positive power line, a ground power line, and four signal lines.
When the power of the personal computer is turned on, the host controller
54
is supplied with system power VDDsys which is generated by the system power circuit
53
. Furthermore, the I/F controller
55
is supplied with operation power VDDif by way of the regulator
56
, the diode
58
, and the regulator
57
. When the power of the personal computer is cut off, the supply of system power VDDsys from the system power circuit
53
is stopped. This opens the host controller
54
.
If the digital camera and the color page printer are activated in this state, the regulator
57
is provided with cable power VDDcab from the digital camera via the first cable
61
and the first connector
51
(or from the color page printer via the second cable
62
and the second connector
52
). The regulator
57
generates the power supply VDDif based on the cable power VDDcab and activates the I/F controller
55
with the power supply VDDif. Accordingly, even if the power of the personal computer is off, the I/F controller
55
receives data from the digital camera via the cable
61
and the first connector
51
and transmits the data to the color page printer via the second connector
52
and the cable
62
.
However, if the power of the personal computer is turned on when the I/F controller
55
is performing data transmission, power supply noise mixes with the system power VDDsys. The power supply noise also mixes with the operation power VDDif of the I/F controller
55
. As a result, the I/F controller
55
may function abnormally and affect the transmission of data in an undesirable manner.
SUMMARY OF THE INVENTION
Accordingly, it is an objective of the present invention to provide an interface circuit that prevents power supply noise from affecting the interface.
To achieve the above objective, the present invention provides a method for controlling a system power supply to an interface circuit that is operated by at least the system power supply or an external power supply. The interface circuit performs data transmission.
In one aspect of the present invention, the method includes generating a trigger signal indicating that the system power supply has gone on, and closing a switch between the system power supply and the interface circuit at a timing that does not affect the data transmission in accordance with the trigger signal.
In another aspect of the present invention, the method includes generating a trigger signal indicating that the system power supply has gone off, and opening the switch at a time that does not affect the data transmission in accordance with the trigger signal.
In a further aspect of the present invention, the method includes generating a first trigger signal indicating that the system power supply has gone on, closing the switch at a timing that does not affect the data transmission in accordance with the first trigger signal, generating a second trigger signal indicating that the system power supply has gone off, and opening the switch at a timing that does not affect the data transmission in accordance with the second trigger signal
The present invention also provides an interface circuit for performing data transmission. The interface circuit includes an interface controller operated by at least a system power supply or an external power supply, and a switch connected between an interface controller and a system power circuit for conducting system power.
In one aspect of the present invention, the interface controller of the interface circuit includes a control signal generating circuit for generating a control signal that closes the switch at a timing that does not affect the data transmission in accordance with a trigger signal, which indicates that the system power has gone on.
In another aspect of the present invention, the interface controller of the interface circuit includes a control signal generating circuit for generating a control signal that opens the switch at a timing that does not affect the data transmission in accordance with a trigger signal, which indicates that the system power has gone off.
In a further aspect of the present invention, the interface controller of the interface circuit includes a control signal generating circuit for generating a first control signal that closes the switch at a timing that does not affect the data transmission in accordance with a first trigger signal, which indicates that the system power has gone on. The control signal generating circuit further generates a second control signal that opens the switch at a timing that does not affect the data transmission in accordance with a second trigger signal, which indicates that the system power has gone off.
The present invention further provides a data transmission device including an interface circuit that performs data transmission, and a host controller connected to the interface circuit, wherein control signals are transmitted between the host controller and the interface circuit to control data transmission therebetween. The interface circuit includes an interface controller operated by at least a system power supply or an external power supply, and a switch connected between the interface controller and a system power circuit for conducting system power.
In one aspect of the present invention, the interface controller of the interface circuit provided in the data transmission device has a control signal generating circuit for generating a control signal that closes the switch at a timing that does not affect the data transmission in accordance with a trigger signal, which indicates that the system power has gone on.
In another aspect of the present invention, the interface controller of the interface circuit provided in the data transmission device has a control signal generating circuit for generating a control signal that opens the switch at a timing that does not affect data transmission in accordance with a trigger signal, which indicates that the system power has gone off.
In a further aspect of the present invention, the interface controller of the interface circuit provided in the data transmission device has a control signal generating circuit for generating a first control signal that closes the switch at a timing that does not affect the data transmission in accordance with a first trigger signal, which indicates that the system power has gone on. The control signal generating circuit further generates a second control signal that opens the switch at a tim
Oi Kenji
Shimizu Takashi
Takase Hiroshi
Ueno Hirotaka
Arent Fox Kintner & Plotkin & Kahn, PLLC
Fujitsu Limited
La Anh
Wu Daniel J.
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