JPH01121945A - Single chip microcomputer - Google Patents

Abstract

PURPOSE:To perform check without consuming the capacity of a ROM by incorporating the ROM and an EEPROM in a single chip microcomputer and using a checking program stored in the EEPROM. CONSTITUTION:In case of self-diagnostic check of a CPU 103 and a peripheral circuit or the like, the program including desired check items is written in an EEPROM 104 from the external. Thereafter, a switching signal 118 is made active, and then, a program counter 101 receives this signal and outputs an address signal 108 to the EEPROM 104. A selecting circuit 105 selects an output code 110 of the EEPROM 104 and inputs it as an instruction and data to the CPU 103. Thus, the program written in the EEPROM 104 from the external is successively executed and the output corresponding to the program is outputted from a port 106 and a terminal 117 and is detected in the external. Unless the program written in the EEPROM 10 is changed by the operation of the CPU 103 or another check, check is executed again if the signal 118 is made active.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to single-chip microcomputers. More specifically, the present invention relates to a novel configuration of a single-chip microcomputer in which read-only nonvolatile memory, readable and electrically writable nonvolatile memory, etc. are mounted on one chip.

BACKGROUND OF THE INVENTION Conventionally, in single-chip microcomputers of this type, each element constituting the computer, such as a CPU section, a register section, an instruction decoder, a timer, a board, etc., has been manufactured correctly, and manufacturing processes have been carried out to determine whether they operate correctly. It has an inspection function during the process or at the time of shipment.

This test is actually executed according to a predetermined program, but for this purpose, the single-chip microcomputer is equipped with a part of the read-only memory (hereinafter referred to as ROM) or a separate test ROM. Programs for testing were previously stored in the memory and executed as needed.

Further, with the progress of LSI technology, the degree of integration of transistors in integrated circuits has been increasing, and it has become common for single-chip microcomputers to have approximately one transistor on one wafer.

However, on the other hand, it is necessary to inspect at each stage of manufacturing, such as in the wafer state and package state, whether all transistors on the manufactured integrated circuit are free from defects and are operating normally.

The effectiveness of such a test can be increased by performing it under conditions close to the actual operating state of the integrated circuit, so conventionally, a test program is stored in a part of the internal ROM storage area. The above program was stored and the program was executed by operating a specific external terminal, and the execution results were inspected. It is also common to separately provide a dedicated ROM that stores a test program, store the test program in the storage area of this ROM, and execute the test to perform the test.

Problems to be Solved by the Invention The above-mentioned conventional single-chip microcomputers that store testing programs in part of the normal ROM storage area cannot open the testing program storage area to the user. This has the disadvantage that the capacity of the ROM that can be provided for the user's use is reduced.

On the other hand, if a ROM for inspection is installed separately from the normal ROM, R cannot be used for purposes other than inspection.
The drawback is that the OM (which is completely unnecessary for the user) increases the chip size and increases cost.

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the prior art described above and to provide a novel single-chip microcomputer that can perform testing without wasting ROM capacity.

Means for Solving the Problems According to the present invention, in a single-chip microcomputer incorporating a first read-only nonvolatile memory and a second nonvolatile memory that can be read and electrically written and erased, 2 non-volatile memory is activated by the single-chip microcombinator itself.
Alternatively, the single-chip microcomputer is configured so that arbitrary contents can be electrically written or erased by a predetermined operation from outside, and the contents stored in the first non-volatile memory can be used as instructions or data. and means for reading and executing contents stored in the second non-volatile memory as instructions or data, and further comprising means for reading instructions or data from the first non-volatile memory or A single-chip microcomputer is provided that includes means for selecting whether to read instructions or data from a second nonvolatile memory.

Operation The single-chip microcomputer according to the present invention is R
Its main feature is that it has a built-in OM and EEPRQM, and is particularly configured to be able to execute a test program stored in an EEPROM.

The present invention will be described in more detail below with reference to the drawings, but what is disclosed below is only one embodiment 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 the configuration of a single-chip microcomputer constructed according to the present invention.

This single-chip microcomputer has a built-in ROM 102 (for example, 8 bits) and an EEPROM 104 that have the same word length, and these ROMs
Selectively sends one of the outputs of 102 and 104 to the CPU U2.
It includes a selection circuit 105 for transferring data to O5. Further, the address output from the program counter 101 is R
It is configured to be supplied to both OM2O3 and EEPROM104.

The EEPROM 104 can also be directly controlled from the outside, and an address signal and a data input terminal 1 are input from the address input terminal 114.
By inputting data from 15 and a write/erase signal from control terminal 116, it is possible to write or erase data to any address. (In order to facilitate this, it is common to be able to write/erase directly from the outside as described above.)

In normal operation, program counter 101 is stored in ROM1.
02 head address signal 107 is output, and an output code 109 output from ROMIQ2 is manually inputted to CPU 2O5 as an instruction and data via selection circuit 105. In this state, the E E PROM2O3 is controlled by the CPU 103 and is used as a nonvolatile RAM.

In this embodiment, when performing a self-diagnosis test on the CPU 103 and peripheral circuits, etc., write a program including desired test items from the outside to the EEPROM 104 and activate the switching signal 118.
1 receives this and outputs an address signal to the EEPROM 104, and the selection circuit 105 selects the address signal to the EEPROM 104.
Select the output code 110 of c as instructions and data.
Manually powered to puto-a.

As a result, programs externally written into the EEPROM 104 are executed sequentially, and outputs corresponding to the programs are output from the port 106 and the output terminal 117 and can be detected externally.

For the above self-diagnosis test, program the EEFROM once.
As long as the contents of the EEPROM 104 after writing are not changed by the operation of the CPU 103 or other tests, testing and retesting can be performed simply by activating the switching signal 118.

In addition, this single-chip microcomputer
Even if the number of terminals after packaging is small and it is not possible to input a program from outside, the above EEP can be applied in the wafer state.
If a program is written to the ROM, a self-diagnosis test can be performed by simply operating the switching signal 118 after packaging.

As described in detail, the single-chip microcomputer according to the present invention is equipped with an EEPROM into which a test program according to the purpose is externally written, and can easily perform self-diagnosis by executing the program in response to instructions from the outside. can be implemented. - On the other hand, since the existing EEPROM is used to store the test program, the user's ROM capacity does not decrease, and there is no need to provide a separate testing ROM.

Furthermore, once a program is written to the EEFROM, as long as the contents of the EEPROM do not change, the test program already written to the EEPROM can be used for subsequent inspections, and the test can be performed simply by manually issuing a test execution request. can be executed.

This has the effect that it can be easily tested even after it is sealed in a package with a small number of terminals, and has the indirect effect that the data retention test of the EEPROM can also be performed by reusing the stored contents of the EEPROM.

Furthermore, since the contents of the test program can be easily changed when writing to the EEPROM, flexible measures such as adding test items to improve the detection rate of defective parts can be easily and flexibly implemented.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of the configuration of a single-chip microcomputer constructed according to the present invention. [Main reference number] 100...Single chip micro combinator,
101...Program counter, 102...ROM. 103...CPU. 104...EEPROM. 105...Selection circuit, 106...Output port, 107.108...Address signal, 109.11
0...Output code, 111...Selected output code, 112...Write data to EEPROM, 113...Output data, 114...EEPROM address input terminal, 11
5'--EEPRO material data input terminal, 116
...EEPROM control terminal, 117 ...output terminal, 118 ...switching signal

Claims (1)

[Claims] A single-chip microcomputer incorporating a first read-only nonvolatile memory and a second nonvolatile memory that can be read and electrically written and erased, wherein the second nonvolatile memory It is configured such that arbitrary contents can be electrically written or erased by the operation of the chip microcomputer itself or by a predetermined operation from outside the single chip microcomputer, and the first nonvolatile memory is means for reading and executing the stored content as an instruction or data; and means for reading and executing the content stored in the second non-volatile memory as an instruction or data; A single-chip microcomputer characterized by comprising means for selecting whether to read data or to read instructions or data from the second nonvolatile memory.