JPH02148233A - Microcomputer - Google Patents

Abstract

PURPOSE:To surely detect a runaway by executing the initialization of a watch dog timer only when an initializing instruction is executed by a specific address which is set in advance. CONSTITUTION:A control part 5 is constitute so that an address signal 6 of an instruction which is being executed at present and an initializing instruction executing signal 7 are inputted, and only when the initializing instruction executing signal 7 is a correct signal, and also, a condition that its executing address signal 6 is a prescribed address is formed, an initializing signal 3 is outputted actually to a watch dog timer 2. Accordingly, probability by which the initialization of the watch dog timer is executed by an instruction code generated by change at the time of runaway is very low. In such a way, such a situation as the watch dog timer is initialized by mistake in the course of runaway and the runaway cannot be detected can be avoided in reality.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to microcomputers. More specifically, the present invention relates to a novel microcomputer configuration that is equipped with a watchdog timer and can effectively detect program runaway.

Conventional Technology One method for detecting runaway in a microcomputer and taking effective countermeasures is to use a circuit called a watchdog timer. That is, the watchdog
A timer is a counter that is initialized every predetermined period of time, and if for some reason the count value is not initialized within this period and the count continues and an overflow occurs, the program The system is configured to generate a predetermined control signal by assuming that the control signal has run out of control.

Problems to be Solved by the Invention The conventional watchdog timer as described above has a configuration in which a count value is initialized by an instruction (hereinafter referred to as an initialization instruction) that is generated every predetermined period. ,
If the same code as the initialization instruction happens to occur when the program runs out of control, the runaway cannot be detected because the initialization will be executed.

That is, for example, if the value of the program counter is destroyed by external noise, the instruction code in the second byte of a two-byte instruction may be executed as the first byte. In this case, even if the subsequent execution of the program is completely out of control, if the instruction code that spans two instructions accidentally becomes the instruction code of the initialization instruction, the watchdog timer will be initialized by mistake. As a result, it is no longer possible to detect a runaway microcomputer.

Therefore, the present invention solves the problems of the prior art described above, and
The purpose of this invention is to provide a microcomputer configuration equipped with a new watchdog timer that can more reliably detect runaway.

Means for Solving the Problems According to the present invention, there is provided a watchdog timer that updates a count value every predetermined period and generates a predetermined control signal when an overflow occurs; The microcomputer is configured to initialize the watchdog timer only when the initialization instruction is executed at a preset specific address. A microcomputer is provided which is characterized in that:

In other words, in the microcomputer according to the present invention, the watchdog function is activated after double confirmation of the address and instruction code.
Performs timer initialization so that accidental code cannot initialize the watchdog timer. Therefore, in the conventional microcomputer runaway detection method described above, if the watchdog timer initialization instruction is accidentally executed during runaway, the watchdog timer has no effect at all. In such a microcomputer, the watchdog timer is not initialized by an accidentally generated initialization command, and the watchdog timer can always effectively detect runaway.

The present invention will be described in more detail below with reference to the drawings, but the following disclosure is only one example of the present invention and does not limit the technical scope of the present invention in any way.

Embodiment FIG. 1 is a block diagram schematically showing a configuration example of characteristic parts of a micro-combination store according to the present invention.

This microcomputer includes a central processing unit 1 that performs arithmetic processing based on a program, a watchdog timer 2 that outputs a runaway detection signal 4 when a runaway is detected as described later, and a watchdog timer 2 that outputs a runaway detection signal 4 as described later. The control unit 5 controls the dog timer 2.

The watchdog timer 2 updates its count value every fixed period, and furthermore, when the count value exceeds a predetermined fixed value and overflows, the watchdog timer 2 outputs a runaway detection signal 4.
is configured to output to the central processing unit 1.

The control unit 5 receives an initialization command generated when the central processing unit 1 is operating normally, and initializes the watchdog timer 2 at regular intervals within a range in which the watchdog timer 2 does not overflow. . Here, the control unit 5 of the microcomputer according to the present invention is configured to receive an address signal 6 of the currently executing instruction and an initialization instruction execution signal 7, and the initialization instruction execution signal 7 is The initialization signal 3 is actually output to the watchdog timer only when the conditions that the signal is correct and the execution address signal 6 is a predetermined address are satisfied.

That is, in the microcomputer according to the present invention, the watchdog timer 2 is not initialized unless both the code of the initialization instruction itself and its address signal are normal. When a microcomputer runs out of control, it is virtually impossible for both the instruction code and address signals to be generated at the same time. Therefore, this microcomputer can reliably detect a runaway.

As described in detail, the microcomputer according to the present invention initializes the watchdog timer after double confirmation of the address and the instruction code. - The probability that timer initialization will be executed is very low. Therefore, it is practically possible to avoid a situation where the watchdog timer is erroneously initialized during a runaway and the runaway cannot be detected.

It is a diagram.

(Main reference number) ■・Central processing unit, 2. Watchdog timer, 3...Initialization signal, 4. Runaway detection signal, 5...control unit, 6.Address signal, 7...Initialization instruction execution signal

Claims (1)

[Claims] A watchdog timer that updates a count value every predetermined period and generates a predetermined control signal when an overflow occurs; and an initialization instruction that initializes the count value of the watchdog timer. The microcomputer is configured to initialize the watchdog timer only when the initialization instruction is executed at a preset specific address. Computer.