JPS6265138A - Discriminating device for reset signal of microcomputer controller - Google Patents

Abstract

PURPOSE:To discriminating a reset state in the runaway mode of a microcomputer from a reset state in the drop mode of voltage, by providing a timer circuit consisting of a resistance, a capacitor, a diode, etc. and deciding the rest state according to the output voltage of the timer circuit. CONSTITUTION:When a microcomputer 1 is in a runaway state, a runaway detecting circuit 6 outputs a reset signal. In such a case, a power supply 3 has no drop of voltage and the output of a timer circuit consisting of a capacitor 5, a resistance 4 and a diode 13 is kept at H. While the charging electric charge of the capacitor 5 is discharged quickly via the diode 13 when a reset signal is delivered from a power supply voltage detecting circuit 7. Then the output of the timer circuit goes to L. As a result, a reset state due to the runaway of a microcomputer can be discriminated from a reset state due to the drop of the power supply voltage. Then the power supply 3 is switched to a back-up power supply 2, etc. by an appropriate program.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a reset signal discrimination circuit that distinguishes between a reset signal when a runaway of a microcomputer is detected and a reset signal when a voltage drop occurs.

[Background of the invention t] As described in the service book of the conventional device ft-t, Hitachi Pal air conditioner issued in May 1981, the microcomputer or LSI of the control device issues a reset signal (f-t) due to an instantaneous voltage drop. When it is read, everything is reset, and there is no need to distinguish between reset signals. To provide a reset signal discrimination device for a microcomputer control device, which can distinguish between microcomputer runaway and voltage drop by providing a simple timer circuit, and enables control according to each case.

[Summary of the invention]

In order to achieve the above object, the present invention connects a diode between the contact point of the resistor and the capacitor and the power source in a CR timer that photovoltaically connects the capacitor through the resistor from the power source. When charging, it takes time to charge the capacitor through the resistor.

When the voltage drops, the charge stored in the capacitor is discharged through the diode. Therefore, it discharges in a short time. When a reset signal is generated, by first inputting the voltage of the capacitor mentioned above, the input becomes low when the voltage drops, and in the case of a reset from the runaway detection circuit,
Since there is no change in the ii source, the input will be at a high voltage. It has a feature that the set signal can be distinguished by this input voltage.

[Embodiments of the invention]

Is this an embodiment of the present invention? 0, which will be explained with reference to FIG. 1. Normally, a power supply voltage is applied from the microcomputer IVc voltage source 3. A runaway detection circuit 6 and a power supply voltage drop detection circuit 7 are connected to the reset terminal 9. Microcomputer backup'
11m2 is connected to the backup power supply terminal 8, and saves the contents of the backup memory when the power supply voltage of the microcomputer decreases.

When the microcomputer goes out of control, the runaway detection circuit 6 outputs a reset signal to the microcomputer reset terminal 9, but the input 12 remains at "H" because the power supply is in a state of flux. When the power supply drops, a reset signal is output from the Kamegen pressure drop detection circuit 7 to the VC. Also at this time, the charge stored in the capacitor 5 is discharged in a short time through the diode 1:l1m.

Therefore, if the control program at reset is made as shown in Figure 2, by first checking the terminal 12 after the reset, it is possible to check that the capacitor 5 is still connected after the power supply voltage has dropped by one level.
Since Vc is not fully charged, the input is rLJ. In the case of rHJ, it is determined that the reset signal is due to microcomputer runaway detection, and runaway processing is performed. In the case of a voltage drop, if the contents of the backup memory are not destroyed, a second process of continuing operation is performed, and if the contents of the memory are destroyed, an initialization process is performed.

Here, the cathode of the diode 130 can also be connected to the output of the source voltage drop detection circuit 7 as in the embodiment of FIG. At this time, the diode 14 is used to prevent the signal from going around.

〔Effect of the invention〕

As explained above, according to the present invention, by simply adding a simple timer circuit using a resistor, a capacitor, and a diode, it is possible to distinguish between a reset when a microcontroller runs out of control and a reset when a voltage drop occurs, so the operation is controlled according to the reset cause VC. It has a certain effect.

[Brief explanation of drawings]

FIG. 1 is a reset signal discrimination circuit diagram showing one embodiment 1+11 of the present invention, FIG. 2 is a program flowchart,
FIG. 3 shows another embodiment, in which the diode l! FIG. 3 is a diagram of a glue set signal discrimination circuit when connected to an i-power supply voltage drop detection circuit.

Claims (1)

[Claims] In a control device with a built-in microcomputer that has a built-in backup memory when the power supply voltage drops and has a structure that can distinguish whether the contents of the backup memory have been destroyed, the reset signal from the microcomputer runaway detection circuit and the If the microcomputer terminal that inputs the reset signal at power-on is the same, install a CR timer that charges the capacitor from the power supply through the resistor, and connect the cathode of the diode from the connection point of the capacitor and resistor to the output of the power supply or voltage drop detection circuit. Connect the anode to the connection point of the capacitor and resistor to the output side of the power supply or voltage drop detection circuit, form a circuit that takes a long time to charge when the power is turned on, and quickly discharges through the diode when the voltage drops, and the microcontroller When a reset signal is input, first, the microcontroller determines whether the reset is caused by a voltage drop or not by checking the voltage of the timer circuit described above.If the reset occurs due to something other than a voltage drop, it is determined that a runaway has occurred, and the voltage is A reset signal discriminating device for a microcomputer control device, characterized in that, in the case of a drop, it is determined whether or not the contents of a backup memory are destroyed.