JPH0212345A - Microcomputer - Google Patents

Abstract

PURPOSE:To avoid a case where a watchdog timer is erroneously initialized during the runaway and this runaway cannot be detected by initializing the watchdog timer only with an initialization instruction for the watchdog timer set in a prescribed address. CONSTITUTION:A 1st control part 5 performs the initialization of a watchdog timer 2 only when an initialization instruction is carried out in a prescribed address. While a 2nd control part 8 produces a runaway detecting signal 10 when a prescribed instruction is carried out in an address other than the prescribed one. Therefore the timer 2 is never initialized even though an initialization instruction executing signal 7 is produced when an address signal 6 has the value other than the prescribed one. Thus it is possible to avoid such a case where the timer 2 is erroneously initialized and a microcomputer is unable to detect the runaway.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting program runaway in a microcomputer, and particularly to a microcomputer that detects runaway using a watchdog timer.

[Conventional technology]

The conventional method for detecting a runaway in a microcomputer using a watchdog timer is that if the count value of the watchdog timer continues to count without being initialized within a predetermined period and an overflow occurs, the program will run out of control. It means looking at it.

[Problem to be solved by the invention]

The watchdog timer used in conventional microcomputers mentioned above has a configuration in which the count value is initialized only by a certain predetermined instruction (hereinafter referred to as an initialization instruction), but it is possible for the watchdog timer to be initialized by accident when a program runs out of control. It has no effect at all if the instruction code of the instruction occurs. For example, if the value of the program counter is destroyed by noise from outside the microcomputer, the instruction code in the second byte of a 2-byte instruction may be executed as the first byte.

In this case, even if the subsequent execution of the program becomes 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. However, the drawback is that the microcomputer cannot detect runaway behavior.

[Means to solve the problem]

The microcomputer of the present invention includes a watchdog timer and an initialization instruction that initializes the count value of the watchdog timer, and only when the initialization instruction is executed at a predetermined address. - A first control section that initializes a timer and a second control section that generates a runaway detection signal when a predetermined instruction is executed at an address other than the predetermined address.

〔Example〕

FIG. 1 is a block diagram of one embodiment of the present invention.

The central processing unit 1 performs arithmetic processing based on a program. The watchdog timer 2 outputs a first runaway detection signal 4 to the central processing unit 1 if the initialization signal 3 is not input within a predetermined period.

The first control unit 5 receives the initialization signal 3 when the address signal 6 of the instruction currently being executed is equal to a predetermined value and an initialization instruction execution signal 7 for initializing the watchdog timer 2 is input. is output to watchdog timer 2. On the other hand, the second control unit 8 outputs a second runaway detection signal 10 to the central processing unit 1 when the address signal 6 is different from the predetermined value and the predetermined command execution signal 9 is input. .

With the above configuration, watchdog timer 2 is not initialized even if initialization instruction execution signal 7 is generated other than when address signal 6 is a predetermined value. It is never initialized. An initialization instruction for the watchdog timer 2 is placed at a predetermined address, and the watched timer can be initialized only when the instruction is normally executed.

When a predetermined instruction is mistakenly executed at an address other than the predetermined address when the program runs out of control, the second runaway detection signal 10 is generated immediately, so the watchdog timer 2
The runaway can be detected earlier than when the first runaway detection signal 4 is generated. The predetermined instruction here is an instruction that must not be placed at any other address than the predetermined address, and if it is executed at any other address than the predetermined address, it is considered to be a runaway program. The predetermined instruction may be a watchdog timer initialization instruction.

〔Effect of the invention〕

As explained above, in the microcomputer of the present invention, by preventing the watchdog timer from being initialized except for the watchdog timer initialization instruction placed at a predetermined address,・This has the effect of avoiding a situation where the timer is initialized and runaway cannot be detected. Furthermore, by adding a function to generate a runaway detection signal when a predetermined command is mistakenly executed at an address other than a predetermined address during a program runaway, there is an effect that runaway can be detected more quickly.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of an embodiment of the present invention. 1...Central processing unit, 2...Group watchdog timer, 3...Initialization signal, 4...
First runaway detection signal, 5...First control unit, 6
... Address signal, 7 ... Initialization command execution signal, 8 ... Mark - second control section, 9 ... Predetermined command execution signal, 1o ... ...Second runaway detection signal. Agent Patent Attorney Susumu Uchihara

Claims (1)

[Claims] In a microcomputer equipped with a watchdog timer and an initialization instruction that initializes the count value of the watchdog timer, the watchdog timer is initialized only when the initialization instruction is executed at a predetermined address. 1. A microcomputer comprising: a first control section that performs the above operations; and a second control section that generates a runaway detection signal when a predetermined instruction is executed at an address other than the predetermined address.