JP2003069395A - Signal detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal detection circuit that can provide a hysteresis characteristic to an external signal received by a microcomputer so as not give a noise to the external signal without incurring a cost increase. SOLUTION: The signal detection circuit for giving an external input to the microcomputer gives a hysteresis characteristic to an external input on the basis of a prescribed signal from the microcomputer and provides the external signal with the hysteresis characteristic to the microcomputer. Thus, the signal detection circuit can provide the hysteresis characteristic to the external signal on the basis of an instruction of the microcomputer for receiving the external signal and processing the signal so as to reduce the number of circuit components such as a comparator that is a source of a cost increase.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal detection circuit for providing a hysteresis characteristic to an external input and inputting an external signal having the hysteresis characteristic to a microcomputer. 2. Description of the Related Art Generally, a signal detection circuit has a hysteresis characteristic so that a signal input to a microcomputer does not enter a noise due to external noise or the like or a ripple of a power supply. It is often done to have. Conventionally, a circuit using a comparator or an operational amplifier is often used for this purpose. However, in such a conventional example, the circuit becomes complicated,
There was a problem that cost increased. FIG. 1 shows a conventional example, in which a comparator 1 is used for a signal detection circuit. I
An external signal is input to N, and the signal detection circuit is connected to the microcomputer. FIG. 2 shows an external signal input to the signal detection circuit and a signal output from the signal detection circuit to the microcomputer. In the case of the configuration as shown in FIG. 1, the detection level of the external signal is as follows: Vref1 = R3 × Vcc / ((R1 + R4) × R2 /
((R1 + R4) + R2) + R3) Vref2 = ((R4 × R3) / (R4 + R3)) × V
cc / (((R4 × R3) / (R4 + R3)) + R2). Thereby, a hysteresis characteristic is given to the external signal input to the microcomputer. An object of the present invention is to provide a signal detection circuit capable of giving a hysteresis characteristic to an external signal input to a microcomputer without increasing noise without increasing noise. It is in. According to the present invention, there is provided a signal detecting circuit for inputting an external input to a microcomputer, the signal detecting circuit being configured to output the external input based on a predetermined signal from the microcomputer. The signal detection circuit is characterized in that a hysteresis characteristic is given to an external input, and an external signal having this hysteresis characteristic is input to the microcomputer. That is, a hysteresis characteristic can be given to an external signal on a signal detection circuit by an instruction of a microcomputer which receives and processes an external signal, and circuit components such as comparators which increase costs can be reduced. . FIG. 3 shows a signal detection circuit according to an embodiment of the present invention mounted on various devices. The signal detection circuit is connected to an INT terminal (interrupt detection terminal) of the microcomputer. Base resistors R1 and R2 are connected to the base of the transistor Q1 of the signal detection circuit.
R2 is not grounded but is connected to the output port P1 of the microcomputer. P1 has an open drain specification. When P1 is off and the Vbe voltage of the transistor Q1 is 0.6 V, the detection level (Vref) of the external signal input to IN is Vref = (R1 + R3) × 0.6 / R1. When the microcomputer detects the falling edge of the signal, software is set to turn on P1. When P1 turns on, the detection level (Vre
f) is Vref = (((R1 × R2) / (R1 + R2)) + R
3) × 0.6 / ((R1 × R2) / (R1 + R2)) Next, when a rising edge is detected, P1 is turned off. Then, the detection level returns to Vref = (R1 + R3) × 0.6 / R1. As described above, if P1 is turned on and off each time a signal is received, a hysteresis characteristic can be given to the external signal input to the signal detection circuit as shown in FIG. The present invention is not limited to the embodiment described above, and various modifications can be made within the scope of the claims.

[Brief description of the drawings] FIG. 1 is a signal detection circuit diagram of a conventional example. FIG. 2 is a diagram showing an input signal and an output signal of the circuit. FIG. 3 is a signal detection circuit diagram according to the embodiment of the present invention. [Explanation of symbols] Q1 transistor R1, R2, R3 resistance

Claims (1)

1. A signal detection circuit for inputting an external input to a microcomputer, wherein a hysteresis characteristic is given to the external input based on a predetermined signal from the microcomputer, and an external signal having the hysteresis characteristic is provided. A signal detection circuit for inputting a signal to the microcomputer.