JPH02278342A - Microcomputer - Google Patents

Abstract

PURPOSE:To prevent the abnormal action of a system by outputting an interruption request signal from a comparison circuit, permitting an interruption control circuit to generate interruption and taking measures to a runaway with the program of an interruption processing when data of an output circuit changes. CONSTITUTION:When a micro computer executes a write instruction, eights bits data are written into output latches 1-8 from internal part data buses 17-24, and the parity of eight bits data is simultaneously generated in a parity generation circuit 27. At that time, a write signal 25 is inverted in an invertor circuit 31 and a parity generation circuit 28 comes to be non-selective. When the write instruction is not executed on the other hand, the parity generation circuit 28 is selected, and the parity of eight bits data of the output latches 1-8 is generated. Data on the parity generation circuits 27 and 28 are inputted to a the comparison circuit 29, and the interruption request signal 32 is outputted to the interruption control circuit 30 when data are different. Thus, the runaway of the system can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a microcomputer, and particularly to a microcomputer having a function to prevent a system from running out of control.

[Conventional technology]

A conventional microcomputer will be described in detail with reference to the drawings.

FIG. 2 is a block diagram showing an example of a conventional microcomputer.

In the microcomputer shown in FIG. 2, when data is written to the output circuit 26 by a program (hereinafter referred to as a write command), the output circuit 26 outputs the same data to output terminals 9 to 16 until the next write command is executed. Continue outputting.

[Problem to be solved by the invention]

The conventional microcomputer described above does not change the state even if the output terminal is affected by external noise, surge, etc. and the data in the output circuit changes. This has the disadvantage that it prevents the normal operation of the system because it cannot detect the

SUMMARY OF THE INVENTION An object of the present invention is to provide a microcomputer that has a function to prevent a system from running out of control when data in an output circuit changes independently of a write command.

[Means to solve the problem]

The microcomputer of the present invention is a microcomputer having an output circuit that writes data by executing a program and outputs the n-bit data (n is a positive integer) to the outside in parallel. first and second parity generation circuits that generate parity for n-bit data; (8) comparing the first and second parity generation circuits;
A comparison circuit that outputs a comparison signal; and (C) an interrupt control circuit that operates based on the comparison signal.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

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

When the microcomputer shown in FIG. 1 executes a write command, the write signal 25 becomes valid and 8-bit data is written into the output latches 1-8 from the internal data buses 17-24.

At the same time, parity of 8 bit data is generated by the parity generation circuit 27. At this time, the write signal 25 of the parity generation circuit 28 is inverted by the inverter circuit 31 and becomes non-selected.

On the other hand, when a write command is not executed, the parity generation circuit 28 is selected and generates parity for the 8-bit data of output latches 1-8.

The data of the parity generation circuit 27 and the parity generation circuit 28 are input to the comparison circuit 29.

As a result of the comparison, if the data in the parity generation circuit 27 and the parity generation circuit 28 are different, the interrupt control circuit 3
The interrupt request signal 32 is output to 0.

〔Effect of the invention〕

In the microcomputer of the present invention, when the data of the output circuit changes due to the influence of external noise or surge, the comparator circuit outputs an interrupt request signal, and the interrupt control circuit generates an interrupt. By taking measures against runaway in the program, it is possible to prevent abnormal system operation.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional example. 1 to 8...Output latch, 9 to 16...
Output terminals, 17-24...Internal data bus, 2
5...Write signal, 26...Output circuit, 27.28...Parity generation circuit, two...
... Comparison circuit, 30 ... Interrupt control circuit, 31 ... Inverter circuit, 32 ...
-Interrupt request signal.

Claims (1)

[Scope of Claims] A microcomputer having an output circuit that writes data by executing a program and outputs the n-bit data (n is a positive integer) to the outside in parallel, comprising: (A) data written to the output circuit; first and second parity generation circuits that generate parity of n-bit data; (B) comparing the first and second parity generation circuits;
A microcomputer comprising: a comparison circuit that outputs a comparison signal; (C) an interrupt control circuit that operates based on the comparison signal.