One-chip microcomputer system

Details One-chip microcomputer system One-chip microcomputer system

1998-09-04

2001-07-24

Hjerpe, Richard (Department: 2774)

Computer graphics processing and selective visual display system

Display peripheral interface input device

Including keyboard

C345S169000, C341S020000, C341S022000, C341S026000

Reexamination Certificate

active

06266049

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a one-chip microcomputer system, and more specifically to a one-chip microcomputer system which is mounted on an electronic register including a keyboard switch (keyboard matrix) and a display device such as a 7-segment light-emitting diode (LED) and a fluorescent display tube, a POS terminal device, a video tape recorder (VTR), and other electrical appliances.
2. Description of the Related Art
In apparatuses such as the above-mentioned electronic register, there has been a demand for a display device with high brightness and outstanding viewability, a miniaturized accommodating capacity, and a high-speed keyboard input. A conventional example which tries to satisfy such a demand is disclosed in Japanese Laid-open Publication Nos. 59-185389 and 5-325720.
Japanese Laid-open Publication No. 59-185389 discloses a miniaturized and inexpensive apparatus in which display control means and input control means are driven in time division.
Japanese Laid-open Publication No. 5-325720 discloses an inexpensive LED driving apparatus in which the number of components is reduced by driving an LED and scanning a keyboard switch in time division.
According to the above-mentioned prior arts, driving a display and scanning a keyboard switch are serially performed in a time sequence. Hereinafter, these prior arts will be described in detail.
FIG. 23
is a view showing a conventional one-chip microcomputer system. The one-chip microcomputer system includes a microcomputer
1000
, a keyboard switch
2
, and display LED modules
3
,
4
, and
5
.
The keyboard switch
2
includes a number of switches S
00
to S
03
, S
10
to S
13
, and S
20
to S
23
arranged in a matrix. The display LED modules
3
,
4
, and
5
each have a similar configuration. The display LED module
3
will be described as an example. The display LED module
3
includes 7 LEDs D
3
-
1
to D
3
-
7
. The LEDs D
3
-
1
to D
3
-
7
are connected in series to current restricting resistors R
30
to R
33
and R
40
to R
42
, respectively. Anode sides of the LEDs D
3
-
1
to D
3
-
7
are collectively connected to transistors Q
1
, Q
2
, and Q
3
which are driven with a select signal for selecting one of the display LED modules
3
,
4
, and
5
. Cathode sides of the LEDs D
3
-
1
to D
3
-
7
are connected to segment driving ports P
30
to P
33
and P
40
to P
42
. One end of each of base resistors R
10
, R
11
, and R
12
are. connected to the transistors Q
1
, Q
2
, and Q
3
for driving each LED, respectively. The other end of each of the base resistors R
10
, R
11
, and R
12
are connected to output ports P
10
, P
11
, and P
12
of the microcomputer
1000
, respectively.
One end of each of diodes D
10
, D
11
, and D
12
are connected between the base resistors R
10
, R
11
, and R
12
and the output ports P
10
, P
11
, and P
12
. The other end of each of the diodes D
10
, D
11
, and D
12
are connected to the keyboard switch
2
. The diodes D
10
, D
11
and D
12
prevent failure caused by a short-circuit of the output ports P
10
, P
11
, and P
12
in the case where two or more key switches are simultaneously pressed, as well as malfunction of a key input.
The leading ends of return lines from. the keyboard switch
2
are connected to ports P
20
, P
21
, P
22
, and P
23
of the microcomputer
1000
. A return signal is input from the keyboard switch
2
to the ports P
20
, P
21
, P
22
, and P
23
. Pull-up resistors R
20
, R
21
, R
22
, and R
23
are connected in the middle of the return lines.
In the above-mentioned structure, the output ports P
10
, P
11
, and P
12
work as the output ports of a select signal for a display, as well as the scanning output ports of the keyboard switch
2
. The microcomputer
1000
sequentially transmits a select signal from the output ports P
10
, P
11
, and P
12
in such a manner that a signal at only one port becomes a low level, and outputs an LED driving pattern synchronized with the transmitted select signal to the segment driving ports P
30
to P
33
and P
40
to P
42
, whereby a display corresponding to each select is performed:
Furthermore, in scanning the keyboard switch
2
, the microcomputer
1000
investigates an input pattern of the ports P
20
to P
23
to which a return signal is input from the keyboard switch
2
while one scanning signal is at a low level. Thus, it can be recognized which key switch is pressed.
FIG. 19
is a view showing an operation timing of the one-chip microcomputer system shown in FIG.
23
.
The microcomputer
1000
outputs a select signal at a low level through the output port P
10
at ti to select one of the display LED modules
3
,
4
, and
5
. The microcomputer
1000
outputs LED driving signals from the segment driving ports P
30
to P
33
and P
40
to P
42
to display a number. A direction in which an LED driving signal travels may be reversed. At t
2
, all of the select signals output from the output ports P
10
to P
12
are turned off (high level). At t
3
, the subsequent select signal output from the output port P
11
is turned on (low level), and LED driving signals for an LED corresponding to the select signal is output. Thereafter, a display is performed in a similar manner up to the select signal output from the output port P
12
.
Herein, a period in which no select signals are output is provided between t
2
and t
3
. The purpose of this is to prevent a display pattern of the previous digit from being displayed for a short period of time during the subsequent digit after switching of a select signal. This period (between t
2
and t
3
) corresponds to a blanking period. Accordingly, a display is processed during a period T
1
from t
1
to t
7
.
Next, during a period T
2
from t
9
to t
12
, the microcomputer
1000
turns off all the display patterns, and outputs a keyboard scanning signal to the output ports P
10
to P
12
. Between t
9
and t
10
, the microcomputer
1000
reads an ON/OFF state of the keyboard switch
2
corresponding to the select signal output from the output port P
10
at a timing
81
, through the ports P
20
, P
21
, P
22
, and P
23
. Thereafter, in a similar manner, the microcomputer
1000
reads an ON/OFF state of the keyboard switch
2
corresponding to the select signal output from the output port P
11
at a timing
82
and reads an ON/OFF state of the keyboard switch
2
corresponding to the select signal output from the output port P
12
at a timing S
3
.
As described above, in the one-chip microcomputer system shown in
FIG. 23
, driving of a display and scanning of a keyboard matrix are serially performed in a time sequence.
A control system in which driving a display and scanning a keyboard switch are serially performed in a time sequence has the following problems.
Since a drive duty ratio of a display is decreased by the period T
2
, a high-brightness LED which is expensive and difficult to obtain should be used.
SUMMARY OF THE INVENTION
A one-chip microcomputer system of the present invention includes: a display driving circuit for driving a display device; a scanning circuit for outputting a key scanning signal to scan a keyboard switch; a common port used for scanning the keyboard switch and driving the display device; and a controller for controlling parallel processing of scanning the keyboard switch and driving the display device.
In one embodiment of the present invention, the display driving circuit includes a division section for time-dividing information displayed on the display device on a digit basis and a division section for time-dividing information displayed on the display device on a segment basis, and the system further includes a switch for selectively switching the division sections.
In another embodiment of the present invention, the above-mentioned one-chip microcomputer system further includes a counter for measuring a predetermined period of time from an ON timing of a display scanning signal output from the display driving circuit, wherein the controller detects an output signal from the counter.
In another embodi

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