JP2003023350A - Input circuit for controller having microcomputer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an input circuit for controller having microcomputer with which a protecting element on the signal input circuit of a controller having a microcomputer can be eliminated, a number of parts is decreased and costs can be reduced. SOLUTION: In the input circuit for the controller having a microcomputer 1, the port of the microcomputer 1 is set to an output port at ordinary time and the port of the microcomputer 1 is set to an input port for each of prescribed timing, or only for a period from the reading start of the input signal to the end when control software requests an input signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device having a microcomputer for inputting input signals such as sensor signals and digital signals, and more particularly to surge voltage (hereinafter
(Referred to as surge)), and an input circuit of a control device having a microcomputer having an enhanced protection function against surge.

[0002]

2. Description of the Related Art Generally, a control device having a microcomputer requires an input circuit for clamping a voltage in order to protect an internal circuit from noise and surge coming to each input / output terminal. For the port protection of the microcomputer, for example, the port of the microcomputer is protected by using an input circuit including an excessive current prevention resistor and a Zener diode.

[0003]

Conventionally, in a control device having a microcomputer, it is necessary to provide a protective element on a signal input circuit of the control device having a microcomputer for the purpose of protecting a port of the microcomputer from a surge. It was The present invention has been made in view of the above problems, and an object thereof is to eliminate the protective element on the signal input circuit of the control device having the microcomputer while ensuring the high reliability of the system. Another object of the present invention is to provide an input circuit of a control device having a microcomputer, which can reduce the number of parts and reduce the cost.

[0004]

[Means for Solving the Problems] To achieve the above object,
An input circuit of a control device having a microcomputer of the present invention is basically an input circuit of a control device having a microcomputer having an input / output port provided with a plurality of input / output terminals. It is characterized in that it is provided with a port switching means which is normally set to the output port and sets the port of the microcomputer to the input port only when the input signal of the microcomputer is read. A specific aspect of the input circuit of the control device having the microcomputer of the present invention is characterized in that a resistor for consuming surge power is installed between the port of the microcomputer and the input signal line.

With the input circuit of the control device having the microcomputer of the present invention configured as described above, for example, when the control software requests an input signal, the microcomputer is read only from the start to the end of reading the input signal. The computer port is set as an input port, and the surge applied during this short time is absorbed by the electrostatic discharge prevention diode built in the microcomputer to protect the port from the controller with a microcomputer. It is possible to eliminate the protection element on the input circuit that was necessary for the above.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of an input circuit of a control device having a microcomputer of the present invention will be described in detail below with reference to the drawings.

First, the basic idea of the present invention will be described. The input terminal of the microcomputer requires an input circuit to protect it from surges.
A microcomputer protection port is protected by using a protection element such as a diode.

The inventors of the present invention have to say that the output terminal of the input / output terminals of the microcomputer is connected to a relatively large output buffer, and this serves as a protection element.
In an electronic control unit equipped with a microcomputer, attention is paid to the fact that the input signal is input for an extremely short period of time at each predetermined timing or control software request, as compared with the case of an output signal. By constantly using the protection circuit of the output buffer, the number of protection elements on the signal input circuit of the control device is reduced.

That is, in an input circuit of a control device having a microcomputer, a surge is absorbed at all times by setting a port of the microcomputer as an output buffer having a high current driving capability, and the current is limited by a resistor. When the software for executing on the microcomputer requests an input signal, the port of the microcomputer is set as the input port only during the period from the start to the end of reading the input signal, and it is applied during this short time. The surge is absorbed by the diode for preventing electrostatic breakdown built into the microcomputer. This allows
In a control device having a microcomputer, it becomes possible to eliminate a protection element for protecting a port of the microcomputer in a circuit for inputting a signal to the microcomputer.

FIG. 1 is a diagram showing a configuration of an input circuit of a control device having a microcomputer according to an embodiment based on the above basic idea. This embodiment is an example applied to an electronic control unit equipped with a microcomputer for inputting various signals. In FIG. 1, reference numeral 1 is a microcomputer for controlling the entire electronic control unit, 2 is a control device having the microcomputer 1, 3 is a diode for preventing electrostatic breakdown, 4 is a battery, 5 is an output buffer with a microcomputer, Reference numeral 6 is an input buffer incorporated in a microcomputer, R1 is an input protection resistor, and RL is a load resistor. The operation of the input circuit of the control device having the microcomputer configured as described above will be described below.

FIG. 2 is a flow chart for explaining the operation of this embodiment. In the figure, S indicates each step of the flow. First, in step S1, the port is always set as an output port, and in step S2, it is determined whether or not there is an input signal request from the control software. If there is no input signal request, wait until there is an input signal request. If there is an input signal request, the port is temporarily set to the input port in step S3, the corresponding signal is read from the input port set in step S4, and the process returns to step S1 to set the port as the constant output port.

FIGS. 3 and 4 are timing charts for explaining the operation of this embodiment, FIG. 3 is a timing chart for explaining the operation before the control of FIG. 2, and FIG. 6 is a timing chart for explaining the operation of the present embodiment. Consider a case where in the control device 2 having the microcomputer 1, a surge due to an inductive load or a terminal disconnection of the battery 4 is applied to the signal input circuit of the control device 2. The surge applied to the control device 2 having the microcomputer 1 passes through the resistor R1 and reaches the port of the microcomputer 1.

At this time, assuming that the port of the microcomputer 1 is always set to the input port as shown in FIG. 3B, as shown in FIG.
All surges superimposed on the input signal of (a) continuously flow to the electrostatic breakdown prevention diode 3. The time is about 10
It is about 0 msec, and is a diode 3 for preventing electrostatic breakdown.
Has only an energy resistance enough to prevent electrostatic discharge, and the microcomputer 1 may be destroyed. Therefore, in the conventional example shown in FIG. 3, the signal input circuit of the control device 2 having the microcomputer 1 is provided with the protection element in order to prevent the microcomputer 1 from being destroyed.

On the other hand, in the present embodiment, as shown in the flow chart of FIG. 2, the port is always set to the output port, and the surge is absorbed by the output buffer having a high current driving capability. Further, the electrostatic breakdown preventing diode 3 exhibits more resistance to short-time current and single-shot surge application than in the case of continuous surge application.

Next, as shown in FIG. 4 (b), the control software requests an input signal and sets the port as an input port only from the start of reading the input signal to the end of the reading. The period for setting this port as an input port is on the order of μsec, which is extremely short compared with the period for setting a port as an output port (10 to several tens of msec).

As a result, as shown in FIG. 4 (c), the surges absorbed by the electrostatic breakdown preventing diode 3 are short-lived (about 10 μsec) or less and only single-shot. In the example of FIG. 4, since the port is always set as an output port, the surge 11 shown in FIG. 4 (a) is not applied to the electrostatic breakdown preventing diode 3 and is an output buffer having a high current driving capability. Only the next surge 12 is absorbed by the electrostatic breakdown prevention diode 3 for an extremely short time (about 10 μsec). The electrostatic breakdown preventing diode 3 is not destroyed because the surge energy during this period is small and it is a single shot.

Here, the setting method of the input protection resistor R1 is as follows.
The surge current absorbed by the electrostatic breakdown prevention diode 3 is within the rating of the electrostatic breakdown prevention diode 3, and a resistance value that does not affect the system even if the port of the microcomputer 1 is set as an output port. Choose.

The period for setting the port of the microcomputer 1 as the input port is determined by the input capacitance (about 20 pF) parasitic on the input buffer 6 of the microcomputer 1 and the impedance of the input circuit and the external circuit. Also sets a period in which the input capacitance parasitic on the input buffer 6 is sufficiently charged. As described above, the microcomputer 1 can operate normally without being damaged by the surge and can read the input signal correctly.

As described in detail above, according to the present embodiment, in the input circuit of the control device having the microcomputer 1, the port of the microcomputer 1 is always set to the output port, and the control software is set at every predetermined timing. When the input signal is requested by the microcomputer, the port of the microcomputer 1 is set as the input port only from the start to the end of reading the input signal. Can be configured using the internal electrostatic breakdown prevention diode 3 and the internal output buffer 5 of
Conventionally, it is possible to eliminate the protection element on the input circuit which was conventionally required for port protection in a control device having a microcomputer, and it is possible to reduce the cost of parts.

Here, the input circuit of the control device having the microcomputer according to the present invention can be applied to a control unit (for example, an electronic control unit), and a high reliability system can be constructed. However, the present invention is not limited to such a control unit, and can be applied to any device as long as it is a control device having a port for inputting an input signal to a microcomputer. that's all,
Although the embodiments of the present invention have been described in detail, the present invention is not limited to the above embodiments, and various modifications can be made in design without departing from the spirit of the invention described in the claims. It is a thing.

For example, various design changes can be made to the switch for switching the input / output buffer, the type and number of diodes, the connection state, and the timing of reading the input signal. It is also possible to configure an equivalent circuit by using an element (for example, a thermistor) having a resistance element as the load of the input protection resistor R1.

[0022]

As can be understood from the above description, the input circuit of the control device having the microcomputer according to the present invention is provided on the signal input circuit of the control device having the microcomputer while ensuring the high reliability of the system. It is possible to eliminate the protection element, and it is possible to reduce the number of parts and reduce the cost.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an input circuit of a control device having a microcomputer according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of the input circuit of the control device having the microcomputer according to the embodiment of the present invention.

FIG. 3 is a timing chart for explaining the operation of the input circuit of the control device having the microcomputer according to the embodiment of the present invention.

FIG. 4 is a timing chart for explaining the operation of the input circuit of the control device having the microcomputer according to the embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Microcomputer 2 ... Control device 3 ... Microcomputer built-in electrostatic breakdown prevention diode 4 ... Battery 5 ... Microcomputer built-in output buffer 6 ... Microcomputer built-in input buffer R1 ... Input protection resistance RL ... Load resistance

Continued front page    (72) Inventor Yasuo Noto             Hitachinaka City, Ibaraki Prefecture 2520 Takaba             Ceremony Company Hitachi Ltd. Automotive equipment group (72) Inventor Yuji Yoshioka             2477 Takaba, Hitachinaka City, Ibaraki Prefecture Stock Association             Inside Hitachi Car Engineering F term (reference) 5J056 AA01 AA04 BB43 BB46 BB52

Claims (2)

[Claims] 1. An input circuit of a control device having a microcomputer having an input / output port provided with a plurality of input / output terminals, wherein the microcomputer port is always set as an output port, and an input signal of the microcomputer is set. An input circuit of a control device having a microcomputer, comprising port switching means for setting a port of the microcomputer to an input port only when reading. 2. The input circuit of a control device having a microcomputer according to claim 1, wherein a resistor for consuming surge power is installed between a port of the microcomputer and an input signal line.