JPH07302250A - Latchup prevention device for semiconductor circuit - Google Patents

Abstract

PURPOSE:To prevent a semiconductor circuit from being destructed by latchup phenomenon of by detecting the presence/absence of the application of a power supply voltage to the other semiconductor circuit connected to the input/output port of a microcomputer and switching the input/output mode of the input/output port corresponding to the presence/absence of the application of the power supply voltage. CONSTITUTION:At the time of starting an operation, the input/output port 2 of the microcomputer 1 is set as an input port. When it is detected that the power supply voltage is not applied through a pull-up resistor 6 to the input terminal 4 of the other semiconductor circuit 3 connected to the input port, switching the input port to an output port is cancelled and the input port remains. When it is detected that the power supply voltage is applied, the input/ output port 2 is switched to the output port and data are transferred from the microcomputer 1 to the other semiconductor circuit 3. Thus, the semiconductor circuit 3 is prevented from being destructed by the latchup phenomenon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a latch-up of a semiconductor circuit for controlling a latch-up of the semiconductor circuit by controlling an input / output port for transferring data with an input / output terminal of another semiconductor circuit in a microcomputer. Regarding prevention device.

[0002]

2. Description of the Related Art Conventionally, in a micro computer having an input / output port capable of switching one port between input and output, when this port is used as an output port to another semiconductor circuit, it is connected to this port. The output mode is set from the beginning regardless of whether the power supply voltage is applied to the other semiconductor circuit. However, particularly in a semiconductor circuit such as a CMOS-IC, if a voltage is applied to the input terminal when a power supply voltage is not applied, a latch-up phenomenon occurs in which an excessive current flows from the input terminal toward the inside of the circuit, and is destroyed. There was a problem.

[0003]

As a conventional measure for solving such a problem, as a conventional measure, a protection circuit is provided at an input terminal, the output timing of a microcomputer, and a semiconductor circuit connected to this microcomputer. There is a problem in that a circuit is required to properly set the power supply rise timing, and the cost for that is increased and a space for arranging components is required.

The present invention has been made to solve the above problems, and prevents a semiconductor circuit connected to an input / output port capable of switching between input and output of a microcomputer from being destroyed by a latch-up phenomenon. It is an object of the present invention to provide a latch-up prevention device.

[0005]

In order to achieve the above object, a semiconductor circuit latch-up prevention apparatus of the present invention has a pull-up means for dividing and applying a power supply voltage between a power supply terminal and an input terminal. A semiconductor circuit, input mode setting means for setting an input / output port to an input mode at the start of operation, voltage detection means for detecting a voltage of an input terminal of the semiconductor circuit from the input / output port set to the input mode, and the voltage And a microcomputer having input / output mode switching means for switching the input / output mode of the input / output port according to the detection result of the detection means, and if necessary, the microcomputer switches the mode depending on the detection result of the voltage detection means. Standby means for detecting the voltage detection means again after waiting for a certain time when it is determined that the means cannot be switched. And it has a configuration with.

[0006]

According to the present invention, in the above structure, the input mode setting means sets the input / output port of the microcomputer as an input port when the operation is started, and the voltage detecting means is an input terminal of another semiconductor circuit connected to the input port. When it is detected that the power supply voltage is not applied to the output port via the pull-up means, the switching of the input port to the output port is stopped and the input port remains as it is. When it is detected that the power supply voltage is applied, the input / output port is switched to the output port, and the microcomputer operates to transfer data to another semiconductor circuit.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A latch-up prevention device for a semiconductor circuit according to an embodiment of the present invention will be described below with reference to the drawings. Figure 1
2 is a block diagram of a semiconductor circuit latch-up prevention device according to an embodiment of the present invention, and FIG. 2 is a flow chart for explaining the operation of the circuit of FIG. In FIG. 1, an input terminal 4 of another semiconductor circuit (IC) 3 is connected to an input / output port 2 of a microcomputer 1, and a power supply voltage is connected between this input terminal 4 and a power supply terminal 5 of the semiconductor circuit 3. Pull-up resistor 6 as pull-up means for detecting the presence or absence
Are connected. A power switch 7 is connected between the power supply terminal 5 and the power supply 8 of the semiconductor circuit 3, and the power supply terminal 9 of the microcomputer 1 is directly connected to the power supply 8 for convenience of description.

With the above-mentioned configuration, the operation will be described with reference to the flowchart of FIG. First, as shown in FIG. 2, the input / output port 2 of the microcomputer 1 is set as an input port by a program in step S10 (input mode setting means), and an input is accepted from the port 2 of the microcomputer 1 in step S11, and then step S12. At, the voltage of the input terminal 4 of the semiconductor circuit 3 is checked (voltage detecting means). Input terminal 4
Since there is a pull-up resistor 6 between the power supply terminal 5 and the power supply terminal 5, when the power supply voltage is applied to the power supply terminal 5 of the semiconductor circuit 3, the input voltage from the port 2 becomes High level. When the voltage is at the high level, the microcomputer 1 switches the input / output port 2 to the output port by the program in step S13 (input / output mode switching means), and switches the circuit so that the output is sent from the port 2 in step S14. In step S15, data transfer is performed to the input terminal 4 of the semiconductor circuit 3.

When the voltage level is low in step S12, it is determined that the power supply voltage is not yet applied to the semiconductor circuit 3 or has not risen sufficiently,
After waiting for a certain time in step S16, step S17
In step S18, the counter is incremented, and if the counter does not reach the predetermined number in step S18, the process returns to step S11. When the counter reaches a predetermined number in step S18, it is determined that there is an abnormality, the input / output port remains in the input mode, and the program operates to turn off the power supply of the microcomputer 1 in step S19. If the design is such that the power supply voltage is already applied when the port 2 is set to the input in step S10, the steps of step S16 to step S18 as the standby means are omitted and the input is performed in step S12. If the voltage of the terminal 4 is low, the power is turned on in step S19.
You can set it to ff.

As described above, according to this embodiment, the input / output port 2 of the microcomputer 1 is switched so as to function as an input port at the beginning of the program,
The voltage of the input terminal 4 of the semiconductor circuit 3 connected to this is checked, and if it is High after the judgment, the data is transferred to the input terminal 4 of the semiconductor circuit 3 by using the input / output port 2 as an output port by the program. Therefore, it is possible to prevent the semiconductor circuit 3 from being destroyed by the latch-up phenomenon due to the application of the output from the input / output port 2 when the power supply voltage is not applied to the semiconductor circuit 3 connected to the microcomputer 1.

As the pull-up means for detecting the presence / absence of application of the power supply voltage, a diode in the forward direction with respect to the power supply voltage may be provided instead of the pull-up resistor 6 of the embodiment. It is needless to say that it is possible to detect the presence or absence of the above, a capacitor may be provided in place of the pull-up resistor 6, and a separate circuit using a transistor may be provided. Further, depending on the semiconductor circuit (IC), since a resistor, a diode, or the like is connected from the power supply terminal to the input terminal as an internal circuit, the voltage of the input terminal 4 may switch depending on whether or not the power supply voltage is applied. In this case, The same operation as this embodiment can be performed without adding any parts.

[0012]

As is apparent from the above-described embodiments, the semiconductor circuit latch-up prevention apparatus according to the present invention determines whether or not the power supply voltage is applied to another semiconductor circuit connected to the input / output port of the microcomputer. Have means to detect,
By switching the input / output mode of the input / output port according to the presence / absence of the application of the power supply voltage, it is possible to prevent the semiconductor circuit from being damaged by the latch-up phenomenon by adding a few components such as a latch-up resistor.

[Brief description of drawings]

FIG. 1 is a block diagram of a latch-up prevention device for a semiconductor circuit according to an embodiment of the present invention.

FIG. 2 is a flowchart showing the same operation.

[Explanation of symbols]

 1 microcomputer 2 input / output port of microcomputer 3 semiconductor circuit (IC) 4 input terminal 5 power supply terminal 6 pull-up resistor

Claims (2)

[Claims] 1. A semiconductor circuit having a pull-up means for dividing and applying a power supply voltage from a power supply terminal to an input terminal; an input mode setting means for setting an input / output port to an input mode at the start of operation; Voltage detection means for detecting the voltage of the input terminal of the semiconductor circuit from the input / output port set to the mode, and input / output mode switching means for switching the input / output mode of the input / output port according to the detection result of the voltage detection means. A latch-up prevention device for a semiconductor circuit including a microcomputer having the same. 2. The semiconductor circuit according to claim 1, wherein the microcomputer has standby means for detecting the voltage detection means again after waiting for a certain period of time when it is determined that the mode switching means cannot switch based on the detection result of the voltage detection means. Latch-up prevention device.