Electrical computers and digital data processing systems: input/ – Intrasystem connection – Bus interface architecture
Reexamination Certificate
2000-08-30
2003-11-11
Lefkowitz, Sumati (Department: 2189)
Electrical computers and digital data processing systems: input/
Intrasystem connection
Bus interface architecture
C710S015000, C710S072000, C714S005110
Reexamination Certificate
active
06647452
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a connection unit for a peripheral device which is connected to a host by using, for example, a Universal Serial Bus (USB) interface. More particularly, the invention relates to a connection unit for a peripheral device that automatically recovers the connection when an abnormality occurs in the communication between the peripheral device and the host.
2. Description of the Related Art
An example of a conventional connection arrangement between a host and a peripheral device is illustrated in FIG.
5
. In particular,
FIG. 5
shows a block circuit diagram for a connection between a conventional USB-compatible peripheral device (terminal)
10
and a host (computer unit)
2
. The peripheral device
10
that is to be connected to the host
2
via a USB may be one of various types of devices, such as a keyboard, a mouse, a printer, a speaker, a game controller, etc.
In
FIG. 5
, he USB is formed of four lines, such as a pair of data lines (D+ line and D− line), a power line (Vcc), and a ground line (G).
As shown in
FIG. 5
, a USB port
3
is provided in the host
2
, and a USB controller
11
is provided in the peripheral device
10
. The USB controller
11
is connected to the USB port
3
via a USB-compatible cable
4
.
The data line D− of the USB port
3
is connected to one end of a pull-down resistor R
1
, and the data line D+ of the USB port
3
is connected to one end of a pull-down resistor R
2
. The other ends of the pull-down resistors R
1
and R
2
are connected to ground lines G.
In the peripheral device
10
, one end of a pull-up resistor R
3
is connected to the D− line and the other end is connected to the power line (Vcc).
With the configuration illustrated in
FIG. 5
, when the peripheral device
10
is not connected to the host
2
, the potential at a point P is 0 volts (low state). When the peripheral device
10
is connected to the host
2
, the D− line, the D+ line, the power line Vcc, and a ground line of the peripheral device
10
are connected to the counterparts of the host
2
, and the potential at the point P is increased (high state). When the host
2
identifies such a potential increase, it determines that the peripheral device
10
is connected to the host
2
. Simultaneously, the host
2
starts to perform a polling operation by calling the peripheral device
10
at regular intervals so that mutual communication is established between the host
2
and the peripheral device
10
. During the polling operation, in response to receiving a calling signal from the host
2
, the peripheral device
10
returns a signal to the host
2
. The peripheral device returns this signal regardless of whether or not the peripheral device
10
is being operated.
When the cable
4
is disconnected to remove the peripheral device
10
from the host
2
, the point P is connected to the ground line G and thus decreases to 0 volts. A voltage or potential drop is detected in the host
2
. From the voltage drop the host
2
determines that the peripheral device
10
is disconnected.
In this manner, by monitoring whether the potential at the point P is in the high state or the low state, the host
2
is able to determine whether the peripheral device
10
is connected or disconnected.
If, however, during polling there is no answer from the peripheral device
10
in response to three consecutive calls by the host
2
, the host
2
discontinues the polling to the peripheral device
10
, thereby interrupting the communication between the host
2
and the peripheral device
10
. In order to recover from the interrupted communication, the cable
4
of the peripheral device
10
must first be disconnected from the USB port
3
so that the potential at the point P drops to a ground potential (low state). The cable
4
must then be re-inserted into the USB port
3
so that the potential is again raised to the high state. Alternatively, an operating system loaded on the host
2
must be restarted.
The peripheral device
10
, on the other hand, has a resetting (initializing) function. For example, when a malfunction occurs in the peripheral device
10
(such as a voltage change, the departure of processing from a fixed program routine, or a memory malfunction) the peripheral device
10
automatically detects such a malfunction and performs the resetting operation. If there is no answer from the peripheral device
10
in response to the polling by the host
2
a predetermined number of times and communication therebetween is interrupted during the occurrence of such a malfunction, the peripheral device
10
performs the resetting operation to recover. When, a signal cannot be transmitted from the peripheral device
10
to the host
2
, in spite of the resetting operation by the peripheral device
10
, it is necessary to either remove the cable
4
from the USB port
3
and re-insert it to the USB port
3
, or restart the system.
SUMMARY OF THE INVENTION
Accordingly, in order to solve the above-described problems, it is an object of the present invention to provide a connection unit for a peripheral device which automatically recovers from interrupted communication between the peripheral device and a host without the need for a user to restart the system or remove and re-insert a cable.
In order to achieve the above object, according to the present invention, a connection unit is provided for a peripheral device that is connected to a host via a data line. The data line is set to a first state at a predetermined potential (such as a high state) when communication between the peripheral device and the host is performed. The connection unit includes a recovering unit that establishes an apparently reconnected state between the peripheral device and the host by changing the potential of the data line to a second state (such as a low state) from the predetermined potential when the communication between the peripheral device and the host is disabled and then by changing the potential of the data line to the predetermined potential (high state).
With such a recovering unit, even if communication between the peripheral device and the host (polling from the host to the peripheral device) is interrupted, it can be apparently reconnected without the need to physically disconnect them, thereby automatically recovering to the normal communication state. This eliminates the need for the operator to remove and reinsert a cable between the peripheral device and the host or to restart the system.
In one embodiment of the connection unit, the data line may be connected to a ground via a first resistor in the host and may be connected to a power supply via a second resistor in the peripheral device. The recovering unit may establish the apparently reconnected state between the peripheral device and the host by setting the data line to the low state in the peripheral device and then by resetting the data line to the high state.
In the above-described embodiment of the connecting unit, the data line may include a D− line and a D+ line, and the recovering unit may establish the apparently reconnected state between the peripheral device and the host by setting at least one of the D− line and the D+ line to the low state in the peripheral device and then by resetting the data line to the high state.
For example, a switch for controlling the current flow may be provided as the recovering unit on at least one of the D− line or the D+ line of the peripheral device. When the peripheral device detects the interruption of the calling from the host or detects a malfunction occurring in the peripheral device, the switch is controlled to apparently disconnect the D− line or the D+ line between the peripheral device and the host. This decreases the potential of the D− line or the D+ line provided with the second resistor to the ground potential. The host thus determines that the peripheral device is disconnected although it is not
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Lefkowitz Sumati
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