JPH07202660A - Key matrix circuit - Google Patents

Abstract

PURPOSE:To obtain a key matrix circuit where a diode for current sneak path prevention is unnecessitated, responsiveness is excellent and a high speed scan is possible. CONSTITUTION:Plural key switches S11 to S44 for which a matrix array is arrayed are connected with the input/output ports 21 to 24 of a control circuit 2 via the wirings 31 to 34 of a line and are connected with input ports 25 to 28 via the wirings of a column 41 to 44. The input/output ports 21 to 24 are possible to be switched to the both of input/output by the programmable control of the control circuit 2 and the depressing of a key switch is detected by the input port in a state that the only one port is switched to an output side and others are switched to an input side. At this time, because the input/output port except a key switch is switched to the input side even if two or more key switches are simultaneously depressed, the influence of current sneak path is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a key matrix circuit used in equipment such as a numeric keypad device, an intercom device and the like, and more particularly to a key matrix circuit of this type in which parts are simplified and operation response is improved.

[0002]

2. Description of the Related Art A key matrix circuit is a circuit used for an input device such as an intercom device and a numeric keypad device.
As shown in FIG. 2, a plurality of key switches 10 arranged in a matrix and a control circuit (C
PU) 20. In the figure, a 4 × 4 matrix is shown as an example.

Conventionally, in such a key matrix circuit, key switches S ₁₁ to S ₁₁ are arranged in a matrix.
Via wires 41 to 44 of the wiring 31 to 34 and column of S ₄₄ rows, it is connected to the output ports P ₂₁ to P ₂₄ and the input port P ₂₅ to P ₂₈ of the CPU 20. Further, diodes 51 to 54 are inserted in the wirings 31 to 34 of the rows connected to the output ports P _{21 to} P ₂₄ in order to prevent current from flowing to the key switch side. Also input port P ₂₅
Pull-up resistors 61 to 64 (hereinafter referred to as resistors) are connected to the wirings 41 to 44 of the columns connected to P ₂₈ .

In such a configuration, for example, the CPU 2
When only the output port P _{21 of} 0 is set to “L”, when the key switch S ₁₁ is pressed, the current flows to the resistor 61 → wiring 41 → key switch S ₁₁ → wiring 31 → diode 51 → output port P ₂₁ , input port P ₂₅ detects the "L", detects that the key switch S ₁₁ is depressed. Similarly, when the key switch S ₁₂ , S ₁₃ or S ₁₄ is pressed, the input port P ₂₆ , P ₂₇ or P ₂₈ detects "L", and it is detected that any one of these key switches is pressed.

Similarly, the output port P of the CPU 20_{twenty two}Only
In the "L" state, the key switch S_{twenty one}~ S_{twenty four}Is pressed
Can be detected and output port P_{twenty three}Only "L"
The key switch S₃₁~ S₃₄Was pressed
Can be detected and output port P _{twenty four}Only "L" state
Then, key switch S₄₁~ S₄₄Detected that was pressed
it can. Therefore, output port P_{twenty one}~ P_{twenty four}A short cycle
, That is, by sequentially setting to “L” in time division,
It is possible to detect the pressing of all the key switches.

By the way, in such a conventional key matrix circuit, in order to prevent current from flowing to the output port when two or more key switches are simultaneously pressed,
Backflow preventing diodes 51 to 54 are inserted.
For example, when there is no diode, if the key switches S ₁₁ and S ₂₁ are simultaneously pressed when the output port P ₂₁ is “L” (the other output ports are “H”), the key switch S ₁₁
Current flows through the output port P as described above, but the output port P
Output port P from key ₂₂ via key switch S ₂₁ → S _11
A current flows to _21. As a result, the voltage at the input port P ₂₅ becomes an intermediate value, and it becomes impossible to detect whether the key is properly pressed.

[0007]

As described above, the diode for preventing backflow is indispensable in the conventional key matrix circuit, which increases the number of parts, which hinders cost reduction and device size reduction and weight reduction. Further, in the conventional key matrix circuit, there is a problem that it takes time to switch the output port from "L" to "H" or "H" to "L" because the diode is inserted. That is,
For example, when the output port P ₂₄ is "L", the key switch S
_{When 41} is pressed, a current flows through the resistor 61 → key switch S ₄₁ → diode 54 → output port P ₂₄ and input port P _25.
Becomes "L" and the depression of the key switch S ₄₁ is detected, but when the output port P ₂₄ is switched to "H" and the output port P ₂₃ is switched to "L" next, the input port P ₂₅ immediately becomes "L". Instead of "H", the voltage changes as shown in FIG. 3 to "H". Therefore, this input port P ₂₅ is "L".
If the key switch S ₄₁ is pressed in the transition period from “H” to “H”, the input port P ₂₅ detects “L” even though the key switch S ₃₁ is not pressed. Therefore, it is recognized that the key switch S ₃₁ is pressed. In order to prevent malfunction due to such a switching time shift due to the diode, it is necessary to wait for the transitional state at the time of switching when switching the state of the output port in time division, which slows down the key scan speed. There was a problem that the reaction after pressing the key was slow.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a key matrix circuit having a small number of parts and a simple structure and excellent responsiveness.

[0009]

A key matrix circuit according to the present invention which achieves the above object is connected to a plurality of key switches arranged in a matrix and to the key switches through row wirings and column wirings. A control circuit, an input port provided in the control circuit to which column wiring is connected, an input / output port provided in the control circuit to which row wiring is connected, and an input port and an input / output port provided in the control circuit And a pull-up resistor connected to the input / output port, and the input / output port has a switching means for switching between input and output according to a command from the control circuit.

[0010]

By switching the state of the input / output port to either input or output by the programmable command of the control circuit, even if two key switches are pressed at the same time, current flows through the input / output port via these key switches. Can be prevented. Moreover, since this switching is performed by software processing without using a diode, the state of the input / output port can be switched immediately, and the responsiveness of the key operation can be improved. Can be raised.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the key matrix circuit of the present invention will be described in detail below with reference to FIG. The key matrix circuit shown in FIG. 1 has a plurality of key switches 1 (S _{11 to} S ₄₄ ) arranged in a matrix (4 × 4 matrix is shown in the figure for simplicity), and these key switches 1 are connected to each other. A control circuit (hereinafter, referred to as a CPU) 2 that detects pressing of the key switch 1 and performs a specific process is provided. The key switch 1 is connected to the CPU 2 by wirings 31 to 34 in rows and wirings 41 to 44 in columns. There is.

The wirings 41 to 44 of the columns are respectively connected to the CPU 2
Connected to the input ports 25 to 28 of the CPU 2, and the CPU 2 has built-in pull-up resistors R _{5 to} R ₈ for applying a current to the key switch 1 via the input ports 25 to 28. On the other hand, the wirings 31 to 34 of the rows are connected to the input / output ports 21 to 24 of the CPU 2, and these input / output ports 21 to 21 are connected.
The switching switch Sw _{1 is provided} as a switching means for switching the current flow in the input / output ports 21 to 24 to either the input port side or the output port side.
~ Sw ₄ is provided. Each changeover switch Sw _{1 to} S
Each input port connected to one terminal of w ₄ has a built-in pull-up resistor R _{1 to} R ₄ . The level on the output port side connected to the other terminal can be switched to "L" or "H", respectively. The level of the output port and the driving of the changeover switches Sw _{1 to} Sw ₄ are controlled by the CPU 2
It is switched by the command from.

The operation of the key matrix circuit having the above configuration will be described. Input / output port 21
Change only to the output port side of the changeover switch Sw ₁ ,
Set the level to "L". At this time, the changeover switches Sw _{2 to} Sw ₄ of the other input / output ports 22 to 24 are set to the input port side having the built-in pull-up resistor (as shown in the drawing).

When the key switch S ₁₁ is pressed in this state, a current flows through the pull-up resistor R ₅ → key switch S ₁₁ → input / output port 21, and the input port 25 can detect "L". If the key switch S ₁₁ is not pressed, no current flows from the pull-up resistor R ₅ to the key switch S ₁₁ , so that the input port 25 becomes “H”. In the state where only the input / output port 21 is switched to the output port "L", the key switch S connected to the wiring 31 in the same row in the same manner.
_When any one of ₁₂ , S ₁₃ and S ₁₄ is pressed, one of the input ports 26, 27 and 28 becomes “L”, and it is detected that any one of these key switches is pressed. Input port of any two or more of the key switch S ₁₁ connected to the wiring 31 in the same row _{when, S 12, S 13, S} 14 correspond even when co-pressed 26-28
It can be detected depending on the level.

Next, the input / output port 21 is switched to the level "H" side of the output port. At this time, the key switches S ₁₁ , S
₁₂ , S ₁₃ , or S ₁₄ is pressed, input port 2
When any of 5, 26, 27 and 28 is "L", this potential is forcibly switched from "L" to "H". This promptly returns to the standby state for the next detection. When none of these key switches is pressed, the potentials of the input ports 25 to 26 naturally remain "H".

Next, switch the input / output port 21 this time.
Itch Sw₁Switch to the input port side of
Switch Sw for force port 22 only₂Output port
Switch to the side and set the level to "L". In this case
Is the key switch S connected to the wiring 32 of the row._{twenty one},
S_{twenty two}, S_{twenty three}, S_{twenty four}Input when any of the
Any of the ports 25 to 28 becomes "L", and these
It is detected that one of the key switches has been pressed.
It Similarly, only the input / output port 23 is changed over by the switch Sw.
₃If the output port of is switched to "L", wire the row
Key switch S connected to 33₃₁, S₃₂, S₃₃, S₃₄
Switch is pressed to switch the input / output port 24 only.
_FourIf the output port of is switched to "L", wire the row
Key switch S connected to 34₄₁, S₄₂, S₄₃, S₄₄
Each press of can be detected.

By setting the switching settings of the input / output ports 21 to 24, that is, switching from the output port "L" to the output port "H" to the input port, the input / output ports are sequentially switched in a time division manner. It is possible to detect pressing of all the key switches. On the other hand, in this state, when two or more key switches connected to the wirings of different rows are pressed, all the input of the changeover switch except the input / output port to which the wiring of one row is connected. Since it is connected to the port side and pulled up, there is no unnecessary current sneak. For example, when only the input / output port 21 is switched to the output port side and the other input / output ports 22 to 24 are set to the input port side having the built-in pull-up, the key switches S ₁₁ and S ₂₁ are pressed. , Input / output port 2 to which the key switch S ₂₁ is connected
Since 2 is switched to the input port side, the current is pull-up resistor R ₂ → input / output port 22 → key switch S ₂₁
→ Key switch S ₁₁ → Flows with I / O port 21. The output capability “L” of the input / output port 21 is the pull-up resistor R ₂ ,
Since it is sufficiently larger than R ₅ , the voltage of the input port 25 is at a sufficiently low level “L” and even if there is no diode for preventing current sneak between the input / output port 22 and the key switch S ₂₁ , the key switch S It is possible to detect that ₁₁ has been pressed.

As described above, the states of the input / output ports 21 to 24 are arbitrarily switched by the software in the CPU 2 so that the states can be immediately switched. Incidentally, but a structure built in the both CPU pullup resistor R ₁ to R ₄ and R ₅ to R ₈ is in the above embodiment, they may be external, also it can be omitted is there.

In the above embodiments, the case of the 4 × 4 matrix arrangement has been described, but it goes without saying that the present invention can be applied to a larger matrix.

[0020]

As is apparent from the above embodiments, according to the key matrix circuit of the present invention, the port provided in the CPU for selecting the matrix-arranged key switches can be either input or output. Since it can be switched by software, a diode for preventing current from flowing into these ports is unnecessary, which improves the responsiveness of key operations and speeds up key scanning. Further, since the diode is unnecessary, it is possible to reduce the size of the entire device, reduce the number of parts, and reduce the cost.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a key matrix circuit according to the present invention.

FIG. 2 is a circuit diagram of a conventional key matrix circuit.

FIG. 3 is a graph showing a temporal change of a voltage level of an output port in a conventional key matrix circuit.

[Explanation of symbols]

1, S _{11 to} S ₄₄ ... Key switch 2 ... Control circuit (CPU) 21-24 ... I / O port 25-28 ... Input port 31-34 ...... line wiring 41 to 44 ...... column wire R ₁ to R ₈ ...... pullup resistor Sw ₁ to SW ₄ ...... switching Switch (switching means)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasuo Morishita 2-18, Jinnocho, Atsuta-ku, Nagoya, Aichi Aiphone Co., Ltd. (72) Inventor Masahiko Takeda 2-18, Jinno-cho, Atsuta-ku, Nagoya, Aichi Aiphone Incorporated (72) Inventor Takahiro Sakaki 2-18, Kamino-cho, Atsuta-ku, Nagoya, Aichi Aiphone Co., Ltd. (72) Inventor Akira Numata 4-13-6-604 Adachi, Adachi-ku, Tokyo

Claims (1)

[Claims] 1. A plurality of key switches arranged in a matrix, a control circuit connected to the key switches via row wirings and column wirings, and the column wirings provided in the control circuit are connected. An input port, an input / output port provided in the control circuit to which the wiring of the row is connected, and a pull-up resistor provided in the control circuit and connected to each of the input port and the input / output port, The key matrix circuit, wherein the input / output port is provided with switching means for switching between input and output according to a command in the control circuit.