Electrical transmission or interconnection systems – Switching systems – Condition responsive
Reexamination Certificate
1999-01-07
2001-05-15
Jackson, Stephen W. (Department: 2836)
Electrical transmission or interconnection systems
Switching systems
Condition responsive
C307S038000
Reexamination Certificate
active
06232678
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electronic appliance that is connected to another electronic appliance by way of a signal line, and more particularly to an electronic appliance that permits another electronic appliance to recognize establishment of connection between the two electronic appliances by applying a predetermined voltage through a pull-up or pull-down resistor to a signal line connecting the two electronic appliances.
2. Description of the Prior Art
An electronic appliance of the type that is connected to another electronic appliance by way of a signal line is often designed to detect establishment of connection between the two electronic appliances by checking the voltage level on the signal line. Typically, the voltage level to be checked for is set, by the addition of a pull-up or pull-down resistor to the signal line, to be equal to the level of the supplied voltage, the level of ground, or a predetermined level somewhere between these two levels.
FIG. 4
illustrates the outline of a conventional circuit design of an electronic appliance of the type that is connected to another electronic appliance by way of a signal line. This figure illustrates how a first electronic appliance
8
recognizes establishment of connection with a second electronic appliance
9
that is achieved by way of a signal line
7
. The first electronic appliance
8
has a terminal
81
to which one end of the signal line
7
is connected, a detection circuit
82
that monitors the voltage level at the terminal
81
, and a resistor
83
that connects the terminal
81
to a predetermined voltage level. The second electronic appliance
9
has a terminal
91
to which the other end of the signal line
7
is connected, a supplied voltage line
92
that supplies a voltage having a predetermined voltage level Vdd, and a pull-up resistor
93
through which the supplied voltage line
92
is connected to the terminal
91
.
Before the signal line
7
is connected between the terminals
81
and
91
, the voltage level detected by the detection circuit
82
is equal to the voltage level to which the resistor
83
is connected; for example, it is equal to the ground level. As soon as the signal line
7
is connected between the terminals
81
and
91
, the voltage level detected by the detection circuit
82
becomes approximately equal to the predetermined voltage level Vdd, and this causes the electronic appliance
8
to recognize establishment of connection with the electronic appliance
9
.
However, according to the circuit design of the second electronic appliance
9
above, the pull-up resistor
93
keeps the terminal
91
and the supplied voltage line
92
connected all the time; accordingly, connecting the signal line
7
between the terminals
81
and
91
is always accompanied by the appearance of the predetermined voltage level Vdd at the terminal
81
. That is, establishing physical connection between the two electronic appliances
8
and
9
by way of the signal line
7
is equivalent to establishing logical connection between them that can be detected as the presence of the predetermined voltage level Vdd on the signal line
7
. As a result, in cases where the electronic appliance
8
is designed to start a predetermined sequence of operations as soon as it is connected to the electronic appliance
9
, or in cases where the electronic appliance
8
is designed to repeat a predetermined sequence of operations as long as it is connected to the electronic appliance
9
, there is no other way to start or stop such a sequence of operations in the electronic appliance
8
than to connect or remove the signal line
7
physically.
For example, in a case where the electronic appliance
8
is designed to transmit a signal to the electronic appliance
9
immediately or only a short while after establishment of connection between them, it is only after the electronic appliance
9
has become ready for operation that connection can be established between the two electronic appliances
8
and
9
by way of the signal line
7
. A premature attempt to establish connection before the electronic appliance
9
becomes ready for operation results in loss of the signal. Moreover, if an error occurs in the electronic appliance
9
while the electronic appliance
8
is transmitting a signal, the transmission of the signal by the electronic appliance
8
cannot be stopped in any other way than to remove the signal line
7
from the terminal
81
or
91
. Since a terminal for connecting such a signal line is typically located at the back of an electronic appliance, connection or removal of the signal line tends to be troublesome, and thus leads to less efficient use of the electronic appliance.
SUMMARY OF THE INVENTION
An object of the present invention is, in an electronic appliance of the type that is connected to another electronic appliance by way of a signal line and that permits the other electronic appliance to recognize establishment of connection between the two electronic appliances on the basis of the voltage level that appears on the signal line, to make it possible to vary the voltage level with the signal line kept connected.
To achieve the above object, according to the present invention, in an electronic appliance that is provided with a signal terminal for connecting a signal line for connection to another electronic appliance, a constant voltage source for supplying a predetermined voltage, and a pull-up or pull-down resistor for connecting the signal terminal to the constant voltage source and that permits said other electronic appliance to recognize establishment of connection between them by applying the predetermined voltage to the signal terminal, a switch circuit is additionally provided between the pull-up or pull-down resistor and the signal terminal or the constant voltage source. This switch circuit, by being brought into a conducting state or a nonconducting state, serves to turn on or off the application of the predetermined voltage to the signal terminal.
Even if the electronic appliance is connected to the other electronic appliance physically by the signal line, unless the switch circuit is brought into a closed state and thereby the pull-up or pull-down resistor is connected to the signal terminal or the constant voltage source, the predetermined voltage is not applied to the signal line. The other electronic appliance recognizes this state as there being no connection by way of the signal line. In this way, it is possible to create a “logically disconnected” state while keeping the two electronic appliances “physically connected” by the signal line.
The operation of the switch circuit may be controlled by a control circuit provided within the electronic appliance, or may be controlled by feeding the switch circuit with a control signal from the outside. For example, if the switch circuit is controlled by the use of a control circuit that brings it into a closed state as late as a predetermined length of time after the electronic appliance has started receiving electric power, it is possible to keep the other electronic appliance unaware of establishment of connection until the first electronic appliance completes its initial operations, and thus it is possible to let the other electronic appliance start, with appropriate timing, a sequence of operations that should be performed after the completion of the initial operations on the part of the first electronic appliance.
On the other hand, if the switch circuit is so controlled as to be brought into an open state when it receives a control signal from the outside, even a sequence of operations that is supposed to be performed when the electronic appliance is not connected to the other electronic appliance can be performed without the need to remove the signal line. After the completion of such a sequence, the logically connected state can be restored immediately by feeding the switch circuit with another control signal that brings it into a closed state.
REFERENCES:
paten
Arent Fox Kintner & Plotkin & Kahn, PLLC
Jackson Stephen W.
Polk Sharon
Rohm & Co., Ltd.
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