Electrical computers and digital data processing systems: input/ – Input/output data processing – Input/output access regulation
Reexamination Certificate
1997-04-15
2001-02-20
Lee, Thomas C. (Department: 2782)
Electrical computers and digital data processing systems: input/
Input/output data processing
Input/output access regulation
C710S015000, C710S019000, C710S260000, C710S267000
Reexamination Certificate
active
06192425
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a personal computer system, and more specifically to an interrupt line sharing circuit for a personal computer system, for enabling that a common interrupt line is shared by a plurality of instruments, and a method for sharing the common interrupt line.
2. Description of Related Art
In the prior art, this type of interrupt line sharing circuit has been used in a personal computer system having an edged triggered type interrupt line, for the purpose of enabling that one interrupt line is common to a plurality of instruments and shared by the plurality of instruments, as disclosed in Japanese Patent Application Laid-open Publication No. JP-A-3-191410, which corresponds to U.S. Pat. 5,187,781, the disclosure of which is incorporated by reference in its entirety into this application.
Referring to
FIG. 1
, there is shown a circuit diagram of the prior art interrupt line sharing circuit disclosed by JP-A-3-191410 and hence U.S. Pat. 5,187,781. In the shown prior art interrupt line sharing circuit, an instrument
101
A includes a resistor
200
A, a high transistor
213
A, a diode
215
A and a low transistor
211
A connected, in the named order and in their forward direction, in series between a power supply line
107
A and a ground line
109
A. A connection node between the diode
215
A and the low transistor
211
A constitutes an output, which is branched to an interrupt line
217
A connected through a diode
219
A in its forward direction to a common interrupt line
105
.
Similarly to the instrument
101
A, an instrument
101
B includes a resistor
200
B, a high transistor
213
B, a diode
215
B and a low transistor
211
B connected, in the named order and in their forward direction, in series between a power supply line
107
B and a ground line
109
B. A connection node between the diode
215
B and the low transistor
211
B constitutes an output, which is branched to an interrupt line
217
B connected through a diode
219
B in its forward direction to the common interrupt line
105
.
The common interrupt line
105
is pulled down through a resistor
104
, and also connected through a Schmitt trigger circuit
221
to an interrupt request line
102
of a personal computer.
Now, operation of this prior art interrupt line sharing circuit will be described.
In an ordinary condition, the common interrupt line
105
is pulled down to a low level through the resistor
104
, so that the interrupt request line
102
is also at the low level. In the instruments
101
A and
101
B, furthermore, the low transistors
211
A and
211
B are on and the high transistors
213
A and
213
B are off, so that the interrupt lines
217
A and
217
B are also at the low level.
When the instrument
101
A generates an interrupt request, the instrument
101
A turns off the low transistor
211
A and turns on the high transistor
213
A, so that the interrupt line
217
A is brought to the high level. As a result, the common interrupt line
105
is brought to the high level through the diode
219
A, so that the interrupt request line
102
is correspondingly brought to the high level by action of the Schmidt trigger circuit
211
. At this time, if the instrument
101
B does not generate an interrupt request, the low transistor
211
B is on and the high transistor
213
B is off. However, the power supply line
107
A does not short-circuit with the ground line
109
B because of existence of the diode
219
B.
Furthermore, if the instrument
101
B generates an interrupt request, both the interrupt lines
217
A and
217
B are brought to the high level. Although the interrupt line
217
A is brought to the low level as the result of completion of an interrupt processing for the instrument
101
A, since the interrupt line
217
B is still at the high level, the interrupt request line
102
is maintained at the high level, so that the personal computer can acknowledge the interrupt request from the instrument
101
B.
However, in most of conventional personal computer systems which cannot share the interrupt line, the interrupt request signal is defined as an edge trigger type. Therefore, the above mentioned prior art interrupt line sharing circuit which supplies the interrupt request signal of a level trigger type, cannot be applied to the most conventional personal computer systems.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an interrupt line sharing circuit for a personal computer system, and a method for sharing the interrupt line, which have overcome the above mentioned defect of the conventional one.
Another object of the present invention is to provide an interrupt line sharing circuit for a personal computer system, and a method for sharing the interrupt line, both of which enable that one interrupt line is shared by a plurality of instruments, and which can be applied in a personal computer system in which an interrupt request signal is defined as an edge trigger type.
The above and other objects of the present invention are achieved in accordance with the present invention by an interrupt line sharing circuit for a personal computer system, which has a personal computer, a plurality of instruments and one common interrupt line provided in common to the plurality of instruments, wherein the personal computer is configured to perform a predetermined input/output access when the personal computer has completed an interrupt processing, and wherein the interrupt line sharing circuit comprises:
an input/output monitoring means for monitoring whether or not the predetermined input/output access has been performed;
an interrupt line monitoring means monitoring the common interrupt line, for judging that an interrupt processing is started if an interrupt request is sent onto the common interrupt line from any one of the plurality of instruments, the interrupt line monitoring means being connected to the input/output monitoring means, for judging that the interrupt processing has been completed when the input/output monitoring means detects the predetermined input/output access; and
an interrupt line control means coupled to the interrupt line monitoring means, for discriminating a busy
ot-busy condition of the common interrupt line on the basis of the start and the completion of the interrupt processing judged by the interrupt line monitoring means, and for sending the interrupt request generated in the plurality of instruments, to the common interrupt line after the completion of the interrupt processing.
According to another aspect of the present invention, there is provided a method for sharing one common interrupt line provided in common to a plurality of instruments in a personal computer system, comprising the steps of:
causing a personal computer to perform a predetermined input/output access when the personal computer has completed an interrupt processing;
judging that an interrupt processing is started if an interrupt request is sent onto the common interrupt line from any one of the plurality of instruments, and also judging that the interrupt processing has been completed when the predetermined input/output access is detected; and
discriminating a busy
ot-busy condition of the common interrupt line on the basis of the judgement of the start and the completion of the interrupt processing, for sending the interrupt request generated in the plurality of instruments, to the common interrupt line after the completion of the interrupt processing.
As seen from the above, in the present invention, when an interrupt request is sent onto the common interrupt line from any one of the plurality of instruments, namely, an interrupt request signal of the edge trigger type is detected on the common interrupt line, it is judged that the interrupt processing has been started. Completion of this interrupt processing is judged by detecting the predetermined input/output access performed by the personal computer. Thus, if the start and the completion of the interrupt processing can be known, it is
Lee Thomas C.
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
Perveen Rehana
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