JPS5820062B2 - key yomi komi houhou - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a key reading method for an electronic device having a display device such as a fluorescent display tube or an LED.

Recently, the development of LSI (large scale integrated circuit) has progressed, and electronic devices such as electronic desktop calculators and electronic clocks can be manufactured on a single chip, and fluorescent display tubes and LEDs can also be manufactured on a single chip.
It can be driven directly by SI.

However, in such a one-chip LSI, there is a problem with the number of pins (external lead-out terminals), so conventionally, for example, in the case of fluorescent display tubes, the digit signal (digit selection signal) that drives the grid was used as the key reading signal. By doing so, the number of key human pins is reduced.

Figures 1 and 2 show this method, in which 1 is a fluorescent display tube, 2 is a fluorescent display tube;
is the segment electrode, 3 is the grid electrode, 4 is the filament, 5 is the filament power supply, 6 is the keyboard part, 7
is an LSI having a logic circuit.

This reduces the number of pins by sharing the digit signal that drives the grid 3 for key reading, and when the country key is operated, the digit signal D1 is input to the key 1 manually,
This digit signal D1 is detected inside the LSI 7 to determine that the key box has been operated.

However, in a fluorescent display tube, the grid current is about twice as thick as the segment current, and if the east digit output current is increased, the voltage drop at the output MOS transistor of the output buffer circuit becomes significant. Accordingly, the output voltage VOL of the buffer circuit becomes higher than the power supply voltage VSS level.

Since this digit waveform is also used as a key input, the above VoL level must be kept low due to the threshold voltage of the MOS transistor provided at the key input terminal.
S) There was a problem in that the run raster had to be made considerably large in order to reduce its on-resistance.

In addition, in a fluorescent display tube, grid current flows when a digital signal is added regardless of whether it is displayed or not, so it is advantageous in terms of power consumption to narrow or cut the digital signal when not displaying. However, when using a digit signal for key reading, it is necessary to provide the pulse width necessary for key reading.

The present invention has been made in view of the above points, and instead of reading the key using a digit signal, it uses a timing signal dedicated for reading the key and a segment drive signal output terminal as the key input terminal. The present invention aims to provide a key reading method that can reduce size and power consumption.

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a circuit diagram of a key reading section of an electronic device (for example, a calculator) used in the present invention, and FIG. 4 is a timing chart showing its operation.

That is, in the present invention, as shown in FIG. 4, one section in which display data (grid signal and segment drive signal) changes is divided into eight equal parts, and each section is divided into eight equal parts. , 12...
. . . , pulses generated at this time are created as t8.

Among the grid waveform (digit waveform) and segment waveform, for example, 1. , 12.13 is the blanking time t, and the remaining 14 + 15 +...,
It is assumed that the display device is caused to perform display during the period t8.

In addition, as shown in FIG. 3, the segment drive signals A and -P are
Channel type MOS transistors TR1 each have an open drain and are led out to the outside of the LSI via an external lead-out terminal 11, and a load resistor RL is connected between each power supply VKK.

In addition, each of the above terminals is manually operated by one of the timing pulses 11.
They are connected to positive logic AND circuits 12, 13, and 14 of 12°t3, respectively.

Also, a P-channel MO whose source side is connected to the power supply VSS
8l-run raster TR2゜The drain sides of TR3 and TR4 are led out to the outside of the LSI via terminals 16, 17, and 18,
Connect to the keyboard section 19.

That is, in this keyboard section 19, the segment drive signal A
- Each segment drive signal line 20 connected to the corresponding segment electrode of the fluorescent display tube is introduced from each external lead-out terminal 11 of each transistor TR1 corresponding to P, and the number corresponding to t1 to t3 is connected to these signal lines. One end of the keys (three in this case) is connected, and signal lines 21, 22, 23 are introduced from the terminals 16, 17, 18, and the other end of the key corresponding to each of these lines is connected.

Note that 88VDD indicates the internal power supply of the LSI, and VKK indicates the voltage required to light the fluorescent display tube.

However, in a calculator etc., grid signals D1 to D corresponding to n digits and segment drive signal A are used as shown in FIG.
-P is used to dynamically display each digit,
When no keys on the keyboard section 19 are operated, the terminals 16, 17, and 18 of the LSI are not connected to each terminal 11, so the blanking time t during which the timing signals t1 to t3 are output is , the potential of each terminal 11 is always V
When considered in terms of KK level, that is, positive logic, it becomes a low level, and therefore, the outputs of the positive logic AND circuits 13 to 15, 1 to 4, are always at VDD (FIG. 5).

Next, for example, when pressing the key (1), t i fi
At the timing when
is on, so the power supply vss-1-ranjisku TR2
A current path is generated between - load resistance RL - power supply V K K fi, and the terminal 11 corresponding to the segment drive signal A is forced to the VSS level.

Therefore, the output of the AND circuit 13 becomes the VSS level at the tl timing while the key country is being operated.

This is detected inside the LSI to determine that the key (1) has been operated.

Further, even when other keys are operated, the operation key is determined by the operation corresponding to the above case.

It goes without saying that the present invention can also be applied to display devices such as LEDs that perform dynamic display by performing digit selection and segment selection.

As explained above, according to the present invention, by using the segment drive signal terminal as a key input, the digit selection output buffer can easily obtain the current necessary to drive the fluorescent display tube, so that the buffer output There is no problem with OI+II even if the voltage exceeds the key human power threshold voltage.
It is possible to reduce the area occupied by the MO8I-run raster and the like in the output section of the buffer circuit.

Furthermore, in order to limit the power consumption when the fluorescent display tube is not displaying, it is also possible to make the digit selection signal waveform narrower than usual or cut it when there is no display data.

Further, according to the present invention, the segments, drive signal output terminals, and operation keys are made common, and the number of keys is the product of the number of operated keys and the number of loops 1' via the segment drive signal output terminal and the number of segments. Therefore, even if the number of keys increases significantly, the number of LSI terminals will only increase at a small rate.

[Brief Description of the Drawings] Fig. 1 is a circuit diagram for explaining the conventional key reading method, Fig. 2 is a timing chart 1 of the timing signal and digit selection signal inside the LSI in the same circuit, and Fig. 3 is a circuit diagram for explaining the conventional key reading method. A circuit diagram for explaining an embodiment of the present invention, and FIGS. 4 and 5 are time charts showing the operation of the circuit. D1-Dn...Digit selection signal, A-P...
・Segment drive signal, t...Blanking time, t1-t3...Timing signal, 11.1
6 to 18...Terminal, 19...Keyboard section.

Claims (1)

[Claims] 1. A blanking time is provided for the digit selection signal and the segment drive signal, and there are multiple timing signals that occur within this blanking time and have a narrower time width than the blanking time, and these separate signals are A key reading method characterized in that the key is extracted using a route via a signal output terminal, and the operated key is determined based on the extracted signal.