JPS58158726A - Controller for microcomputer - Google Patents

Abstract

PURPOSE:To attain sure microcomputer control, by eliminating defective reset at the application of power supply and enabling the computer to restart against a temporary failure of the microcomputer after resetting. CONSTITUTION:A power-on reset section 1 is formed so that outputs of a self- running multivibrator 9 and a monostable multivibrator 8 are inputted to a reset terminal of the microcomputer 6 via an OR circuit 5a. Resistors RA and RB and a capacitor C2 are connected among terminals 6, 7 of the multivibrator 9, the power line and ground, and the output of a terminal PA0 of the computer 6 is inputted to a terminal 2 of the monostable multivibrator 8. In applying the power supply, a power supply voltage Vcc rises sufficiently and each section starts stable operation. Further, if a failure takes place in the computer 6, the output of the terminal PA0 is not generated, the output of an output terminal 8 of the monostable multivibrator 8 is zero, and the output of the OR circuit 5a passes through the pulse of the multivibrator 9 as it is, allowing to reset the computer 6 and to restart it after a prescribed time.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microcomputer control device having a power-on reset function and an abnormality detection function, and in particular,
Eliminates reset failures when turning on the power (power-on)
Regarding a microcomputer control device that can restart a reset edge in case of a temporary abnormality, for example, the one shown in Fig. A power-on reset unit 1 has two output terminals that output two signals, riJ→rOJ and rOJ→“l” after a predetermined time, and a power-on reset unit 1 that outputs an abnormality signal when an abnormality is detected in the microcomputer 6 (for example, μPD7801). It has a watchdog section 2 for outputting, and a circuit 5 for inputting the outputs of the power-on reset section 1 and the watchdog section 2 to a reset terminal of a microcomputer 6. Power-on reset section l is resistor R1
The watchdog section 2 has a mono multivibrator 8 (for example, 74L8122), and has a 0.45 ew in tw.
The pulse width of the one-shot pulse is determined by Bq K. A resistor Rw and a capacitor Cw are connected, and the output of the inverter 3 is connected to the terminal 2Kv# of the mono multivibrator 8, and the output of the inverter 4 and the mono multivibrator 8 are connected. The output of the terminal 8 is input to the AND circuit 5, and the port terminal PAo of the microcomputer 6 is fully increased by the resistor 7 in consideration of the high impedance state at the time of reset.In the above configuration, the power is turned on. When the terminal voltage of capacitor C1 reaches a predetermined level, the output of inverter 3 changes from "L" to "0" and at the same time the output of inverter 4 changes from "0" to "1", so mono-multivibrator 8 changes from inverter to 3), a one-shot pulse with a pulse width tw is output at the falling edge of the output change. Since the inverter 4 has been outputting "0" for a predetermined period of time (more than several clock pulses of the microcomputer 6), the microcomputer 6 is reset due to the "0" of the AND circuit 5, and from the reset edge KAND circuit 5. "1" based on "1" K of the one-shot pulse of inverter 40rlJ and mono-multivibrator 8
When the microcomputer 6 starts, the microcomputer 6 starts, and the fall of the repeating pulse with a period smaller than the pulse width tw retrigger the mono-multivibrator 8, which is output from the port terminal PAo by the start of the microcomputer 6. On the other hand, if an abnormality occurs in the microcomputer 6 (for example, CPU failure, program destruction, RAM memory corruption), the return pulse output from the microcomputer 6 Since the output of the mono multivibrator 4 becomes "0" when it is gone, it is possible to detect that an abnormality has occurred in the microcomputer 6. However, in conventional microcomputer control devices, the predetermined When the time elapses (the outputs of the inverters 3 and 4 are "l" → "0", "0" → rlJ
If the power supply voltage Vcc has not risen sufficiently, there is a risk of a reset failure even if a reset signal is input. Also, ripples or noise in the power supply may cause the input of the Schmitt trigger circuit to reach the threshold level. If you move it up or down, there is a risk of a reset failure. Furthermore, even if the abnormality in the microcomputer 6 is temporary, once the output of the mono multivibrator 8 becomes "0" and "0" is output from the AND circuit 5, "1" will be output from the AND circuit 5 again. ”
Since the microcomputer 6 is not output, it cannot be restarted even if the microcomputer 6 is reset.

The present invention has been made in view of the above, and is designed to eliminate reset failures when the power is turned on (power-on), and to restart the microcomputer after resetting in the event of a temporary abnormality. When the voltage rises sufficiently, a reset/start repeating pulse is output that has a "0" state for resetting for a predetermined time period and an rxJ state for starting for a predetermined time period, and there is an operation signal that is output in response to the microcomputer operation. To provide a control device for a microcomputer, which prohibits the microcomputer from being reset when the pulse is input, and resets and starts the microcomputer by the pulse when the # operation signal is no longer output. be.

The microcomputer control device according to the present invention will be explained in detail below.

FIG. 2 shows an embodiment of the present invention. The same parts as in No. 1- are indicated by the same reference numerals, so a repeated explanation will be omitted. For example, it has a NE555) and is self-propelled! The output of multivibrator 9 and mono multivibrator 8 is OB.
Resistors RA and R are connected between the terminal 6°7 of the free-running multivibrator 9, which is configured to be input to the reset terminal of the microcomputer 6 via the circuit 51, and the power supply line and ground.
B and a capacitor C2 are connected as shown, and the output of the port terminal PAo of the microcomputer 6 is connected to be input to the terminal 2 of the mono multivibrator 8.

In the above configuration, the time chart in Figure 3 is busy [
To explain the operation, when one power source is turned on at time t1, the power supply voltage Vcc rises sufficiently at time t2, and each part starts stable operation.

The self-propelled multivibrator 9 outputs a pulse 9 with a time limit of "1" of = 0.7 (Ra + RB) in ta and a time limit of Cx-roJ of 0.7 Rml - C2 in tb.
The signal is input to the reset terminal of the microcomputer 6 via the OR circuit 5a. The pulse 9 becomes rlJ at time t32, but since the time limit from time t2 to tsrOJ is short, the microcomputer 6 is not reset and does not start.

When the pulse 9 becomes "0" again at time t4, time [t
b (set to the time required for resetting the microcomputer 6), the microcomputer 6 is reset, and at time t5, the reset terminal input (OR circuit 5a
The microcomputer 6 starts operating when the pulse 9) with an output of 5 m reaches rxJK. Time limit ts (t
s < ta) i If it happens, the boat terminal PA of the microcomputer 6
The output of o falls, and thereafter pulse 6 of period to is output. The mono multivibrator 8 inputs this pulse 6, and is retriggered every time it detects the falling edge of the pulse 6, and is retriggered at time t6.
A one-shot pulse 8 with a pulse intensity tw (1w>tl) is output from. After that, one shot pulse 8
and the pulse 9 of the self-propelled multivibrator 9 are connected to the OR circuit 5a.
The signal is outputted as an output 5a, and the microcomputer 6 continues its operation.

-4. When the pulse 9 with period to is no longer output from the boat terminal PAo due to a temporary abnormality in the microcomputer 6, when time period tw has elapsed from time t7 (time t8)
Since the output 8 of the mono multivibrator 8 becomes roJK (the "0" signal is considered as an abnormal signal), the OR circuit 5
The output 5a of the output 5a passes the pulse 9 of the self-propelled multivibrator 9 as it is and becomes the output 5a. The microcomputer 6 is reset by "0" of the time limit tb of the output 5a (time ts - txo), and starts again from time 110.

This operation of the microcomputer 6 causes the pulse 6 to be output from the boat terminal PAo again, and the mono-multivibrator 8 is triggered at the falling edge 9 of time t11. Thereafter, the same operation is repeated.In the above embodiments, a one-chip microcomputer can be used as the microcomputer 6, but a combination of a general-purpose microprocessor and an output IC may be used instead. However, the self-propelled multi-purpose generator (ibrator) and the mono-martino (digital generator) are not limited to the above-mentioned elements.

As described above, according to the microcomputer control device according to the present invention, when the power supply voltage rises sufficiently, the reset signal has a "0" state for resetting a predetermined time period and an "l" state for starting a predetermined time period. [Repeat pulse for start] is output, and if there is an operation signal that is output in response to the microcomputer operation, the microcomputer is prohibited from being reset even if the pulse is input, and the operation signal is no longer output. When the microcomputer is reset and started by the pulse, it is possible to eliminate reset failures when the power is turned on (power-on), and to restart the microcomputer after resetting in case of temporary malfunction of the microcomputer. can.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing a conventional microcomputer control device, FIG. 2 is a block diagram showing an embodiment of the present invention, and No. 31 is a time chart of FIG. 2. Explanation of symbols 1...Hower-on reset section 2...Watchdog section 6...Microcomputer 8...
%/Multi-Pipe Lake 9... Self-propelled Multi-Pipe Lake Patent Applicant Fuji Xerox - Co., Ltd. Figure 1 Figure 2!

Claims (1)

[Scope of Claims] Means for outputting a reset/start repetition signal consisting of a reset signal for a predetermined time period and a start signal for a predetermined time period; and means for outputting an operation signal in response to the operation of a microcombiator. The microcomputer is prohibited from being reset by the operation signal when the operation signal is output, and when the operation signal is not output, the reset signal and the start of the repetitive reset/start signal are prohibited. A control device for a microcomputer, characterized in that it is reset and started by a signal and outputs the operation signal.