JP2779581B2 - Reset signal generation circuit for microprocessor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reset signal generating circuit for a microprocessor.

[0002]

2. Description of the Related Art A conventional reset signal generation circuit at power-on is generally a circuit using a transistor as shown in FIG. 2 or a dedicated IC or the like.

[0003]

The reset signal generation circuit described in the above prior art has drawbacks such as high cost and a large space requirement due to the use of transistors and dedicated ICs. I was

[0004] When configuring (designing) a microprocessor board, unused gates are left on the mounted general-purpose gate IC.

According to the present invention, the above-mentioned unused gate, that is,
Gates that can constitute inverters (NOT, NOR, NA
It is an object of the present invention to provide a new reset signal generation circuit for a microprocessor in which the above-mentioned defect is solved by a method using two ND gates or the like.

[0006]

In order to achieve the above object, a reset signal generating circuit for a microprocessor according to the present invention comprises a diode D and a resistor Rt connected in parallel, and one terminal of the diode D connected to a capacitor Ct. And a positive voltage is applied to the other pole of the diode D. One end of a resistor Rs is connected in series with the other end of the resistor Rs at a branch point A between the diode D and the capacitor Ct. The inverter is connected to the input end point B of the inverter.
And a positive feedback resistor R in parallel with the output end point C.
f, both ends are connected, and a reset signal output line is connected to an output end side point C.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A reset signal generating circuit for a microprocessor according to the present invention shown in FIG. 1 has a diode D and a resistor Rt connected in parallel, and one pole of the diode D is grounded via a capacitor Ct. A voltage of +5 V is applied to the other pole of the diode D, and one end of a resistor Rs is connected to a branch point A between the diode D and the capacitor Ct, and a plurality of CMOS inverters 1 and 2 are connected in series to the other end of the resistor Rs. Both ends of the positive feedback resistor Rf are connected in parallel with the input end point 3 and the output end point C of the CMOS inverters 1 and 2, and the reset output line 3 is connected to the output end point C. Things.

[0008]

The operation of the reset signal generating circuit for a microprocessor according to the present invention based on the above embodiment will be described. That is, power supply OFF → ON operation: resistance Rt << resistance Rf (R
When the circuit is raised to a value (t is sufficiently smaller than Rf), the voltage at the point A rises slowly from 0 V to 5 V by the time constant of the resistor Rt and the capacitor Ct at the same time when the power is turned on. Accordingly, the voltage Vb at the point B rises with Va according to the equation: Vb = Va ｛{Rf / (Rs + Rf)} (where the condition of Rf / (Rs + Rf)> 0.5 is satisfied). Thus, when the voltage Vb at the point B reaches 2.5 V (the threshold value of the CMOS), the voltage at the point C increases from 0 V to 5 V. This rise of the point C causes the voltage of the point B to rise by the positive feedback resistor Rf,
Accelerate the voltage rise at point C (acceleration by positive feedback). That is, as for the reset output Vc, Va is 2.5 · (Rs + R
f) Invert to +5 V during the time until the voltage rises to / Rf (reset delay time). Power ON → OFF operation: When the power is ON, V
c is + 5V. Here, when the power supply is turned off, the capacitor Ct is immediately discharged via the diode D, and Va drops to 0V. In this way, the point B also becomes lower than the threshold value of 2.5 V according to the equation Vb = VcＶ {Rs / (Rs + Rf)}.
c drops from 5V to 0V. Since the voltage drop at the point C accelerates the voltage drop at the point B by the positive feedback resistor Rf, the reset output becomes 0 V almost at the same time when the power is turned off.

[0009]

According to the present invention, the reset signal generation circuit for a microprocessor according to the present invention has the above-described configuration and functions as described in the above operation, so that a transistor and a dedicated IC are unnecessary. As a result, the cost and space can be saved correspondingly, and an excellent effect of sufficiently achieving the intended purpose can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a conventional example.

[Explanation of symbols]

 D Diode Rt Resistance Ct Capacitor A Branch point Rs Resistance 1 COMS inverter 2 COMS inverter Rf Positive feedback resistor B Input end point C Output end point 3 Reset signal output line

Claims (1)

(57) [Claims] 1. A diode D and a resistor Rt are connected in parallel, one pole of the diode D is grounded via a capacitor Ct, and a positive voltage is applied to the other pole of the diode D. One end of a resistor Rs is connected to a branch point A between the resistor Rs and the capacitor Ct, an inverter is connected in series with the other end of the resistor Rs, and an input end point B and an output end point C of the inverter are connected in parallel. A reset signal generating circuit for a microprocessor, wherein both ends of a positive feedback resistor Rf are connected to each other, and a reset signal output line is connected to an output terminal side point C.