JPH047755A - One-chip microcomputer - Google Patents

Abstract

PURPOSE:To prevent such a defective situation where the function of a one-chip microcomputer is stopped with occurrence of the external noises and the function of an equipment is set in a disable state by providing a stack pointer allowable range storage part and a stack pointer monitoring part. CONSTITUTION:A stack pointer allowable range storing part 8 secures an allowable range of a stack pointer 6, and a stack pointer monitoring part 9 compares the value of the part 8 with the value of the pointer 6 and produces a reset signal when the value of the pointer 6 exceeds its allowable range. If the abnormality of the pointer 6 is confirmed through the monitoring, a one-chip microcomputer is forcibly reset. Thus it is possible to evade such a defective situation where a stack area is shifted due to the external noises, etc., and overlaps a user data area to disturb the normal operation of the one-chip microcomputer and to set the function of the microcomputer in a disable state. Then the reliability of the microcomputer is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a one-chip microcomputer used in video tape recorders and the like.

(Prior art) In recent years, as large-scale one-chip microcomputers have been used to improve functionality and achieve high operability in consumer equipment such as video tape recorders, structured programming has become popular to facilitate program development. techniques have been utilized and stacking functionality has been incorporated into one-chip microcomputers to enable this.

Hereinafter, an example of the operation of the one-chip microcomputer described above will be described with reference to the drawings. FIG. 5 shows a configuration diagram of a conventional one-chip microcomputer with a stack function. In FIG. 5, ■ is a read-only memory (hereinafter referred to as ROM) that stores programs;
3 is an instruction register section, 3 is an instruction control section, 4 is a program counter that indicates the execution address of the program, and 5 is a random access memory (1) used for storing various information, interrupts, return addresses when calling subroutines, and arguments 1.
6 is a stack pointer indicating the address of the stack. The operation will be explained below using a program counter as an example. The stack is FI LO (First InL ast O
ut) type memory, in which data is accumulated in the order of input, and when an output command is given, the data is output in the reverse order of input, with the last input first. In a one-chip microcomputer, when a subroutine call or an interrupt occurs, the value of the program counter 4 at that time is written to the RAM 5.

Add 1 to the value of stack pointer 6. Next, when returning from a subroutine call or interrupt, the value of the program counter is read from the RAM 5 indicated by the value of the stack pointer 6, inputted to the program counter 4, and the instruction at the address indicated by the program counter is sent from the ROMI to the instruction register section 2. The command is read out and executed by the command control unit 3.

(Problem to be Solved by the Invention) However, in the above configuration, if the stack pointer 6 goes out of order due to factors such as external noise, the stack area and user data will be lost as shown in Figure 2. The stack area and the user data area overlap, as shown in Figure 3, and as a result, the RAM used for other purposes is constantly destroyed and the one-chip micro Computer functions do not function properly, and devices such as video tape recorders do not function properly. Furthermore, if the one-chip microcomputer is backed up by a battery or the like, there is a drawback that the device will not return to normal even if the power cord is disconnected until the battery or the like is not discharged.

The purpose of the present invention is to eliminate the drawbacks of the conventional technology, in which the stack area shifts due to external noise, overlaps the user data area, and as a result, the one-chip microcomputer does not operate normally and the entire device becomes inoperable. It is an object of the present invention to provide a one-chip microcomputer that can prevent the device from falling into this state and improve the reliability of the device itself.

(Means for Solving the Problems) The one-chip microcomputer of the present invention has a function of monitoring the stack pointer and forcibly resetting the one-chip microcomputer when an abnormality occurs. - (Function) With the above-described configuration, the stack area shifts and overlaps the user data area due to external noise, and as a result, the one-chip microcomputer does not operate normally and the entire device becomes inoperable. The reliability of the device itself can be improved.

(Embodiment) A microcomputer according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a one-chip microcomputer in an embodiment of the present invention.

In FIG. 1, the same components as those shown in the conventional example are denoted by the same reference numerals, and the explanation thereof will be omitted. 7 is a reset control section of the one-chip microcomputer, 8 is a stack pointer permissible range storage section that indicates the permissible range of the stack pointer 6, and 9 is a stack pointer monitoring section.

The one-chip microcomputer configured as described above will be explained below with reference to FIGS. 1, 2, 3, and 4. Normally, when a subroutine call or an interrupt occurs, a one-chip microcomputer writes the current value of the program counter 4 to the RAM 5 and increments the value of the stack pointer 6 by 1. next,
When returning from a subroutine call or interrupt,
The value of the program counter is read from the RAM 5 indicated by the value of the stack pointer 6, inputted to the program counter 4, and the instruction at the address indicated by the program counter is read out.
Read from OM1 to instruction register section 2, and instruction control section 3
It is executed by

In this case, the stack area and the user data area are used separately as shown in FIG. 2, and the system operates normally. However, if the stack pointer 6 is destroyed due to external noise or the like, the value of the stack pointer becomes a value other than the stack pointer value permitted in the stack pointer tolerance storage unit 8. The stack pointer monitoring section 9 constantly monitors the stack pointer, and outputs a reset command to the reset control section 7 when the above state occurs. As a result, the one-chip microcomputer
- It malfunctions momentarily, but it is initialized and operates normally again. This situation is shown in FIG.

(Effects of the Invention) According to the present invention, by providing the stack pointer tolerance storage unit and the stack pointer monitoring unit, the one-chip microcomputer will stop functioning due to the occurrence of external noise, and the equipment will become inoperable. It is possible to prevent this and realize a more reliable device, which has great practical effects.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a one-chip microcomputer according to an embodiment of the present invention, FIG. 2 is a diagram showing how the RAM of the one-chip microcomputer shown in FIG. Figure 4 shows the state of the RAM in the conventional one-chip microcomputer when it becomes abnormal, Figure 4 shows the movement of the one-chip microcomputer when the stack pointer becomes abnormal, and Figure 5 shows the state of the conventional one-chip microcomputer when the RAM becomes abnormal. FIG. 2 is a configuration diagram of a microcomputer. 1... Read only memory (ROM), 2...
Instruction register unit, 3... Instruction control unit, 4... Program counter, 5... Random access memory (RAM), 6... Stack pointer, 7...
- Reset control unit, 8... Stack pointer tolerance storage unit, 9... Stack pointer monitoring unit. Patent applicant Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] a stack memory used for storing return addresses, arguments, etc. during interrupts and subroutine calls; a stack pointer indicating the address of the stack memory; a stack pointer permissible range storage section giving the range of the stack pointer; a stack pointer monitoring unit that compares the value of the stack pointer with the value of the stack pointer permissible range storage unit and issues a reset signal when the stack pointer takes an unpermitted value, and performs a reset operation based on the reset signal. A one-chip microcomputer characterized in that it is equipped with a reset control section.