Information processing device

Details Information processing device Information processing device

1997-10-08

2001-06-19

Wiley, David (Department: 2155)

Electrical computers and digital processing systems: support

Computer power control

Reexamination Certificate

active

06249874

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an information processing device, and more particularly to an information processing device which is connected to an interface system such as a keyboard interface system and is supplied with power from an upper device to which the interface system is connected and power from an external power source.
In the present specification, a description will mainly be given of a bar code reader connected to a keyboard interface. However, the present invention is not limited to such a bar code reader but includes an information processing device which has a plurality of power supply systems and communicate with a device connected to the information processing device.
2. Description of the Related Art
A system having a bar code reader connected to a personal computer has been widely used to input information represented by a bar code. A bar code reader of so-called touch type is known.
Generally, the bar code reader performs a bar code read operation in which a light is projected onto a bar code and part of the light reflected by the bar code is received. The touch-type bar code reader is equipped with a light-emitting device (LED) as a light source and a two-dimensional CCD (Charge-Coupled Device) serving as a light-receiving element. The operator brings a read window of the touch-type bar code reader into contact with the bar code to be read. Hence, the bar code is illuminated by the light emitted from the LED, and the light reflected by the bar code is received by the CCD, so that information represented by the bar code can be read.
The touch-type bar code reader has a simple, light, easily operable, and less-expensive structure because it does not have any mechanism for deflecting the light for scanning. Further, the touch-type bar code reader does not have any demodulator which demodulates read bar code data and any mechanism which mechanically drives a component. Thus, the touch-type bar code reader has been widely used due to the above advantages thereof.
FIG. 1
is a block diagram of a system structure having such a bar code reader connected between a personal computer and a keyboard. Particularly,
FIG. 1
is a part of the system structure shown in
FIG. 1
, the above part being involved with a signal transmit/receive and a power supply. The system shown in
FIG. 1
includes a personal computer
11
, a keyboard
12
, and a bar code reader
13
, which are respectively equipped with controllers
11
a,
12
a
and
13
a
for controlling the respective operations thereof.
The personal computer
11
, the bar code reader
13
and the keyboard
12
are connected through an interface cable
14
, which includes a transmission line
14
b
and a power supply line
14
a.
The transmission line
14
b
of the interface cable
14
is used to transmit and receive data, and the power supply line
14
a
thereof is used to supply electricity to the keyboard
12
from the personal computer
11
.
The controllers
11
a,
12
a
and
13
a
have respective input and output terminals to which the transmission line
14
b
of the interface cable
14
is connected. Drivers are provided to the output terminals of the controllers
11
a,
12
a
and
13
a.
Electricity for operating the keyboard
12
is supplied from the personal computer
11
via the power supply line
14
a.
The power supply voltage is denoted by V
PC
. The touch-type bar code reader
13
consumes a small amount of power. Hence, in the system shown in
FIG. 1
, the power supply voltage V
PC
of the personal computer
11
is applied to the bar code reader
13
as well as the keyboard
12
so that electricity for operating the bar code reader
13
is supplied from the personal computer
11
via the power supply line
14
a.
A signal which is input when a key of the keyboard
12
is operated or depressed and bar code data input by the bar code reader
13
are transmitted to the personal computer
11
over the transmission line
14
b.
An instruction can also be transmitted to the keyboard
12
and the bar code reader
13
via the transmission line
14
b.
Recently, there has been a demand to efficiently execute the bar code input process of the bar code reader. An advanced bar code reader having high performance is known in which it employs a scanner such as a polygon mirror. The scanner is driven or rotated by a stepping motor which serves as a driving source. The polygon mirror has mirror surfaces by which a light beam emitted from a light source such as a laser diode is reflected so that the bar code is scanned.
In the touch-type bar code reader, the demodulation process for the read bar code data is processed by an upper computer such as a personal computer. However, in this case, the personal computer has an increased load of processing. In order to reduce the load of the personal computer, a modified touch-type bar code reader has been proposed which is equipped with the demodulation circuit which demodulates the bar code data. In this case, the personal computer does not execute the demodulation process.
As the performance of the bar code reader is improved, an increased amount of electricity is consumed therein. The structure shown in
FIG. 1
increases the load of the power source of the personal computer
11
because the bar code reader
13
is supplied with electricity from the personal computer
11
. In some cases, a sufficient amount of energy to drive the bar code reader
13
cannot be supplied thereto.
In order to avoid the above problem, an external power source is provided separately from the power source of the personal computer
11
. The external power source is externally provided to and connected to the bar code reader
13
. An AC adapter is an example of such an external power source.
However, another problem will occur when such an external power source is provided. Generally, electronic devices such as bar code readers and personal computers employ CMOS (Complementary Metal Oxide Semiconductor) circuits because the CMOS circuits consume a relatively small amount of energy. As is well know, the CMOS circuits has a problem so-called “latch up”.
FIG. 2
is a circuit diagram of a CMOS circuit, which includes an n-type MOS transistor and a p-type MOS transistor, the drains of which transistors are connected together. A power supply voltage V
DD
is applied to the CMOS circuit. A symbol V
IN
denotes an input signal, and a symbol V
OUT
denotes an output signal. The CMOS circuit shown in
FIG. 2
functions as an inverter, which consumes a relatively small amount of energy and is thus used widely.
The latch-up occurs in the CMOS circuit shown in
FIG. 2
if the voltage of the input signal V
IN
is greater than the power supply voltage V
DD
.
FIG. 3
is a cross-sectional view of the CMOS circuit shown in
FIG. 2. A
parasitic p-n-p bipolar transistor &agr;
1
and a parasitic n-p-n bipolar transistor &agr;
2
are formed, as indicated by the broken line in FIG.
3
. The above two parasitic bipolar transistors connected in the way indicated by the broken lines form a thyristor. If the thyristor starts to operate, a current continuously flows from the power supply V
DD
to the ground. This phenomenon is called latch-up. In order to release the circuit from the latch-up state, it is necessary to turn of the power supply voltage V
DD
. In some cases, an excessive current flows due to the latch-up, and the circuit may be broken.
The latch-up causes the following problem in a state in which electricity is supplied to either the personal computer
11
or the bar code reader
12
only a signal is transferred over the transmission line
14
b.
In this-state, the latch-up occurs in a CMOS circuit provided in the device supplied with no electricity. The above problem will be described with reference to
FIG. 4
, in which parts that are the same as those shown in
FIG. 1
are given the same reference numbers.
Referring to
FIG. 4
, electricity is supplied to the personal computer
11
, while no electricity is supplied to the bar code reader
13
. In

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