JPH0726753Y2 - Microcomputer signal input circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a signal input circuit of a microcomputer for fetching ON / OFF signals of input contacts based on a timing signal for reading.

[Prior Art] Conventionally, a signal input circuit of a microcomputer of this kind, which takes in an ON / OFF signal of an input contact on the basis of a timing signal for reading, uses a battery power source voltage via a resistor to the input contact to The on / off state is detected based on the voltage across both ends of the microcomputer, and the voltage across this input contact is sampled by a timing signal for reading output from the signal output terminal of the battery-driven microcomputer. Was being input to the signal input terminal of.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional example, when the input contact is on, the detection current always flows from the battery power source through the input contact, so that the average consumption is reduced. There is a problem that the current increases, the heat generation increases, and the battery life shortens.

The present invention has been made in view of the above points, and an object thereof is to reduce the average current consumption, generate less heat, and prolong the battery life. To provide a circuit.

[Means for Solving the Problems] A signal input circuit of a microcomputer of the present invention detects an input contact state based on a reading timing signal output from a signal output terminal of a battery-driven microcomputer, and inputs a signal. In a signal input circuit of a microcomputer adapted to be taken into a terminal, a switching transistor connected between the signal output terminal and the signal input terminal and one end of a series circuit of a capacitor and a resistor are connected to the signal output terminal. A bias circuit that applies a bias to the switching transistor from the connection point of the capacitor and the resistor, and an input contact that is connected in series to the bias circuit and that energizes the bias circuit when the read timing signal is generated to turn on the switching transistor It is a thing.

[Operation] The present invention is configured as described above, and in the signal input circuit of the microcomputer which detects and takes in the state of the input contact based on the timing signal for reading, the signal output terminal of the microcomputer and the signal A switching transistor is connected between the input terminal and the switching transistor is biased from the connection point between the capacitor and the resistor in the series circuit in which the capacitor, the resistor and the input contact are connected in series. Since the current flows only through the input contact, the average current consumption can be reduced, heat generation can be reduced, and the battery life can be extended.

Also, since the input contact is connected in series to the bias circuit consisting of the series circuit of the capacitor and the resistor, when the timing signal for reading is generated when the input contact is turned on, the voltage at the connection point of the capacitor and the resistor is differentiated. As a result, a large current can be momentarily applied to the input contact. That is, while reducing the average current consumption as described above,
Only when the current starts to flow to the input contact, a relatively large current can be passed to remove the surface oxide and the like of the input contact, and as a result, the contact failure of the input contact can be prevented.

[Embodiment] FIG. 1 shows an embodiment of the present invention, in which an input contact SW based on a read timing signal Vo output from a signal output terminal O ₁ of an MC of a microcomputer driven by a battery E. In the signal input circuit of the microcomputer MC that detects the state and captures it at the signal input terminal K ₁ ,
An input contact SW is connected to an input end of a switching circuit SC formed by using a switching transistor Q that operates by using a reading timing signal Vo as a bias voltage, and the output of the switching circuit SC is connected to a signal input terminal K ₁ of a microcomputer MC. It is what you entered. In the embodiment, the switching circuit SC is formed of the switching transistor Q, the diode D, the capacitor C, and the resistors R _{1 to} R _3, and the collector output of the switching transistor Q is the state of the input contact SW. It is input to the signal input terminal K ₁ as the detection signal Vk. Note that a microcomputer
The MC has a plurality of signal output terminals and signal input terminals in addition to the illustrated input / output terminals O ₁ and K ₁ . Also, the reading timing signal Vo output from the signal output terminal O ₁
Is a timing signal appropriately set by the program.

By the way, in the above-mentioned configuration, the capacitor C and the resistor R ₁ constitute a bias circuit for applying a bias to the switching transistor Q, and the input contact SW is connected to this bias circuit via the diode D. The diode D is provided for the purpose of input protection against noise and surge from the outside. If such a diode D exists, the input contact SW
Even if the switch is turned on, the potential at the connection point between the resistor R ₁ and the capacitor C
Vb does not become 0V, but the potential Vb increases by at least the forward voltage drop of the diode D (about 0.6V). Also, the input contact
If a voltage drop occurs due to the ON resistance of SW, the potential Vb will rise further. As described above, when the diode D is provided for input protection, the potential Vb may not be sufficiently lowered, but in the present embodiment, the connection point between the resistor R ₁ and the capacitor C and the pnp type switching transistor. By adopting the configuration in which the resistor R ₃ is inserted between the base of Q, if the resistors R ₁ and R ₃ are set appropriately,
The switching transistor Q can be reliably turned on when the input contact SW is turned on.

The operation of the embodiment will be described below. FIG. 2 is a waveform diagram showing the operation. FIG. 2 (a) is an on / off state of the input contact SW, FIG. 2 (b) is a read timing signal Vo, and FIG. 2 (c) is both ends of the input contact SW. The voltage Va, the figure (d) show the base input voltage Vb of the switching transistor Q, and the figure (e) shows the state detection signal Vk (current i flowing through the resistor R ₂ ). Now, when the input contact SW is off, the reading timing signal Vo is applied to both ends of the input contact SW through the capacitor C, the resistor R ₁ and the diode D.
Since the input contact SW is off and no current flows, the emitter potential and the base potential of the switching transistor Q become the same, the switching transistor Q turns off, and the state detection signal Vk remains "L".

Next, when the input contact SW is turned on, current flows through the input contact SW only during the "H" period of the reading timing signal Vo,
Due to the voltage drop due to this current, the base potential of the switching transistor Q becomes lower than the emitter potential, the switching transistor Q is turned on, and the state detection signal Vk
There "H" becomes, the state of the input contacts SW are incorporated in the signal input contact K ₁ based on the timing signal Vo for reading.

Here, if the reading timing signal Vo is generated when the input contact SW is on, a large current flows momentarily through the resistor R ₁ and the input contact SW in the capacitor C. That is, as shown in FIG. 2 (d), the potential Vb has a differential waveform at the rising of the reading timing signal Vo, so that a large current instantaneously flows through the input contact SW. As a result, the oxide film on the surface of the input contact SW and the insulator attached to the surface of the input contact SW can be removed.

As described above, in the embodiment, the switching circuit that operates using the read timing signal Vo as the bias voltage
Input contact SW to the base of transistor Q which is the input end of SC
Of the switching transistor Q is inputted to the signal input terminal K ₁ of the microcomputer MC as the state detection signal Vk so that the current flows to the input contact SW only at the time of reading. Therefore, the average current consumption can be reduced, the heat generation is small, and the life of the battery E can be extended.

[Advantages of the Invention] The present invention is configured as described above, and in the signal input circuit of the microcomputer for detecting and capturing the state of the input contact based on the timing signal for reading, the signal output terminal and the above A bias circuit, in which a switching transistor connected between a signal input terminal and one end of a series circuit of a capacitor and a resistor is connected to the signal output terminal to apply a bias to the switching transistor from the connection point of the capacitor and the resistor, , And an input contact that energizes the bias circuit to make the switching transistor conductive when a reading timing signal is generated when it is turned on, and a current flows through the input contact only during reading. Average current consumption can be reduced, heat generation is small, This has the effect of extending the battery life.

Also, since the input contact is connected in series to the bias circuit consisting of the series circuit of the capacitor and the resistor, when the timing signal for reading is generated when the input contact is turned on, the voltage at the connection point of the capacitor and the resistor is differentiated. As a result, a large current can be momentarily applied to the input contact, and by removing the surface oxide etc. of the input contact, it is possible to prevent the contact failure of the input contact while reducing the current consumption. Produce an effect.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an embodiment of the present invention, and FIG. 2 is an operation explanatory diagram of the same. C is a capacitor, MC is a microcomputer, O ₁ is a signal output terminal, K ₁ is a signal input terminal, Q is a switching transistor, R ₁ is a resistor, SW is an input contact, and SC is a switching circuit.

Claims (1)

[Scope of utility model registration request] 1. A signal input circuit of a microcomputer, wherein an input contact state is detected on the basis of a timing signal for reading output from a signal output terminal of a battery-driven microcomputer, and the signal is input to the signal input terminal. A switching transistor connected between the signal output terminal and the signal input terminal, a bias circuit for biasing the switching transistor from the connection point of the capacitor and the resistor, and a timing signal for reading when connected in series to the bias circuit A signal input circuit for a microcomputer, comprising: an input contact for energizing a bias circuit to make a switching transistor conductive when generated.