JPS5887635A - Malfunction preventing circuit - Google Patents

Abstract

PURPOSE:To simplify the circuit constitution without the need for externally mounted circuit, by providing a signal generating means for a malfunction prevention circuit and taking an output terminal of a selected decoder as a terminal not in use. CONSTITUTION:An I/O port 12 is connected to a CPU10, output terminals P1- P3 of the port 12 are connected to input terminals A-C of a decoder 14 and to a power supply terminal Vcc via resistors 16, 18 and 20 respectively. Output terminals 00-07 of the decoder 14 are connected to a device to be controlled via buffers B0-B6 respectively and an output terminal 07 is connected to a terminal NC not in use. When an output from the port 12 is given to the decoder 14, the output of the decoder 14 is selected and connected to the terminal 07. Externally mounted circuit is eliminated and the constitution of a malfunction prevention circuit can be simplified.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a malfunction prevention circuit, and more particularly to a malfunction prevention circuit for a microprocessor.

In recent years, microgrocery has been used to control various devices.

is used. Here, the CPU and the controlled device are connected via Ilo/-).

The I10 port is initialized by the CPU after the power is turned on, but it remains in an undefined state for a short time until the initial settings are made. If Ilo #-) is an input, it may be in an undefined state, but if the output signal is in an undefined state, it is unclear how the controlled device will operate, which poses a problem. Conventionally, in order to solve this problem, circuits that monitor specific outputs of the CPU to prevent the CPU from running out of control have been developed, but this requires a dedicated circuit to prevent malfunctions, making the device complex. .

The present invention has been made to address the above-mentioned circumstances, and its purpose is to provide a malfunction prevention circuit for a microprocessor that does not require an external circuit and has a simple configuration.

Hereinafter, one embodiment of the malfunction prevention circuit according to the present invention will be described with reference to the drawings. The drawing is a rough sketch of it. Here, if there are a large number of devices to be controlled and there are not enough terminals for the microcontrollers,
l10f! In recent years, it has become common practice to supply the output signals of (-) to a controlled device via a decoder. In this embodiment as well, it is assumed that the signal is outputted via the decoder. ROM not shown -? Connected to RAM 9 CPU 1 o Connected to I 10 port 12 @
The terminals PI, PI, P3 of l10F/-tozz are connected to the inputs @A, B, C of decoder l4, and are also connected to the power supply terminal VCC through resistors 16, 18, and 20, respectively.
is also connected to. The decoder 14 has eight output terminals 00-07, and the output terminals 00-06 are buffers BO-B6, respectively.
connected to the controlled device via. Output end 00~02
The solenoid 24 as a controlled object via 77B17-B2. 6 and 211, respectively. Output terminal OJ, 04 is buffer B3. They are respectively connected to motors 30 and 32 to be controlled via B4. Output terminals 05 and 06 are connected to light emitting diodes 34 and 36 as controlled objects via buffers B5 and B6. The output terminal 07 is connected to the unused terminal NC and is not connected to the controlled device.

To explain the operation of this embodiment, it is assumed that the relationship between the logic levels of the input and output of the decoder 140 is as shown in the following table.

Here, when the output terminal of the decoder 14 is a logic level, the element connected to the output terminal is energized, and the output terminal becomes a logic level θ.
In the case of a level, it is assumed that the element connected to its output end is not energized.

When the power is turned on, the logic level #'io of the terminal of the I10 port 12 also becomes an undefined state where it is not 1 or 4. However, since the terminal of I10/-)17 is connected to the power supply terminal vcC, it is not in an undefined state, but is in a logical level. As a result, the output terminals 00 to 00 of the decoder 14
06 becomes the logic θ level, and the output terminal 07 becomes the logic level. Therefore, the controlled objects connected to the output terminals 00 to 06 are not energized. Initial settings completed, 110il! -) f
When a signal of a predetermined logic level is supplied from JI to the decoder 14, the decoder 14Fi energizes a predetermined controlled object according to the table described above. Here, CPU 10 is I10
A state in which terminals PZ, Pff, and PJ of port 12 are all logical levels is not set. However, after the initial settings, the CP
U1O may go out of control for some reason, and the terminals PI, I"', and PJ of I10 port 12 may be in an undefined state, similar to when the power is turned on. In this case, Ilo, t?-T1
2 terminals PJ, PJ, PJ are pulled up and all become logic levels. Therefore, when the CPU JO goes out of control, the controlled object C is not energized.

As described above, according to this embodiment, when the controlled object and the microprocessor are connected via the decoder, one output terminal of the decoder is left unused, and when the state of the microprocessor is uncertain, the input of the decoder is Erroneous control can be prevented by setting a specific state in which this unused output terminal is selected. This specific state is set by connecting the output of I10/- to the power supply, thus providing a malfunction prevention circuit with a simple configuration.

This invention is not limited to the embodiments described above, and can be modified in various ways without departing from the gist of the invention. For example, I
There is no need to glue all 10 port outputs! You can use a combination of Luaragu and Gurudown, or you can use Zoldown altogether, 1! In other words, when the output of the I10 port is undefined, the output of the I1041-) is set to a specific state, and the output end of the decoder selected by this specific state is unused.

As described above, according to the present invention, a malfunction prevention circuit for a microprocessor can be realized with a simple configuration.

[Brief explanation of drawings]

The figure shows an embodiment of the malfunction prevention circuit according to the present invention.
This is a diagram. 10... CPUX J2... I10 port, 14.
...Decoder, 16.18.20...Resistor, NC...
・Unused end. Applicant's agent Patent attorney Suzue Takehiko Japanese Patent Application Publication No. 1983-
87635 (3)

Claims (1)

[Claims] A malfunction prevention circuit for a microgrocer connected to an external device via a decoder means, the circuit having a signal generation means, and an output terminal of the decoder means selected when an output signal of the signal generation means is supplied. Malfunction prevention circuit used at the end of use.