JPS5851369A - Microcomputer with test circuit - Google Patents

Abstract

PURPOSE:To prevent the leakage of a program, by comparing data outputted from a program memory with data from an input port, which are arranged in the order of address of this memory, and counting up or down a counter when they coincide with each other. CONSTITUTION:Data of program memory 1 is outputted to a bus line 2 in accordance with an address which is set initially to a program counter 6 preliminarily. The initial value of data, which only a semiconductor maker or a program designer knows, prepared in the order of address of the program memory 1 is inputted from an input port and terminal 4. When data on the data bus 2 and data inputted from the terminal 4 coincide with each other, a comparator 3 outputs a coincidence signal 7 and drives an AND gate 5 by this signal and a test signal 8, and the program counter 6 is counted up or down. The similar operation is executed repeatedly hereafter to compare all data of the program memory. Thus, data of the incorporated program memory are not led out to the external, and surreptitious use is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microcomputer equipped with a program memory test circuit.

Recently, program memory has been transferred to a central control unit (c,p).

So-called single-chip microphone p-con beaters mounted on the same chip as U, ) are applied and used in a wide range of industrial fields. These single-chip microcomputers work as processors with different functions by simply changing the contents of the program memory (hereinafter referred to as data). The most common method is to divide the process into two parts and a part that will not change.

Conventionally, when testing this program memory,
The address of the program memory is incremented or decremented according to the test signal given from the outside, the data of the program memory is output to a specific output terminal, and this data is stored in an external memory etc. in advance and output in an orderly manner. There was a way to judge the quality of a product by comparing it with the correct data. However, according to this method, once anyone knows how to derive the data in the program memory, anyone can know the program data.
There were drawbacks such as complete copying and manufacturing.

The purpose of the present invention is to make it possible to confirm that the data in the built-in program memory is the desired one without ever having to extract the data to the outside, and to prevent the data in the program memory from being copied by a third party. K is offering a microcomputer that has

The present invention provides a microcombiner equipped with a program memory on the same chip whose stored contents are read out in response to commands from a program counter. 9 data supplied from the port and outputs a match signal when they match, and a control means for incrementing or decrementing the program counter according to the match output of the comparing means, the program memory A microcomputer with a test circuit is characterized in that it inspects data without outputting it to the outside.

The present invention will be described in detail below (with reference to the drawings).

FIG. 1 is a partial schematic diagram of an embodiment of the present invention. In the figure, 1 is a program memory, 2 is a pass line, 3 is a comparator that compares the data in program memory 1 and the data from input port 4, 5 is an AND gate, and 6 specifies the address of program memory 1. Address counter, 7 is the match signal of the output of the comparator, 8 is the test signal supplied during testing, 9 is the output port, 10 is the output buffer%11 is the OR gate%13 is the inverter, 14 is output when there is no test signal shows the data to be used. Data in the program memory 1 is output to the pass line 2 according to the address initialized in advance in the program counter 6. On the other hand, initial values of data prepared in the address order of the program memory 1 known only to the semiconductor manufacturer or the program designer are inputted from the input port terminal 4. Here, the comparator 3 compares the data on the data bus 2 and the data at the initial address input from the input port terminal 4, and if they match, it means that the memory semiconductor has been manufactured correctly. If so, a match signal 7 is output. AND gate 5 which is opened by this coincidence signal 7 and test signal 8
That is, when there is a match signal, the program counter 6 is incremented. Thereafter, the program counter 6, which has been incremented by 1 in the same way, outputs the data in the program memory 1 to the pass line 2 in the order of the memory, and sends it to the comparator 3 together with the data output in the order of the program memory addresses input from the input port terminal 4. If the input and the comparison result match, the program counter 6
Increment. Thereafter, by repeatedly executing this process, data in all program memories can be compared. Here, if the comparison result for each address of the program memory is outputted to a specific output port 9 through the OR gate 11 through the output buffer 10 only in the test state, it is possible to easily determine whether the semiconductor product is good or bad. On the other hand, if there is no matching signal, the operation of the program counter 6 is controlled to be stopped, and at the same time, an abnormality can be determined by monitoring the signal from the output port 9.

Note that when there is no test signal 8, this test signal is inverted by an inverter 13, and is passed through the inverter 12 and connected to the OR gate 11, so that the signal 14 is output from the output port 9. You can also.

The twenty-first is a professional drawing of another embodiment of the present invention. In the embodiment described above, the comparison result is directly output to a specific output port 9, but in this embodiment, the comparison result is directly outputted to the specific output port 9, but in this embodiment, the comparison result is directly outputted to the outside by reading out the incremented address by the comparison for each address of the program counter 6. This is to determine whether a desired match has been obtained.

As described above, by using the present invention, it is possible to test memory semiconductors by simply supplying the same data as the built-in program memory from the input port without leading the data in the built-in program memory to the outside. , even if you try to read the match signal and decode the data, for 1000 bytes of program memory, 1000X2 = 512
There are 000 combinations and it is impossible to decipher.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of the invention, and FIG. 2 is a block diagram of a second embodiment of the invention. In the figure, 1...program memory, 2...
...Pass line %3... Comparator, 4...
...Input port, 5...And gate, 6.
....Program counter, 7..Concordance signal, 8..Test signal, 9..Output capo.
), 1G... Output cover, Fa, 11...
Or gate, 12...and gate, 13...
...It is an inverter. n f 2 groups

Claims (1)

[Claims] In a microcomputer equipped with a program memory on the same chip whose contents are read out according to an address command of the program memristor, the data output from the program memory and the data arranged in the address order of this program memory are supplied from the input port. and a control means for incrementing or decrementing the program counter according to the coincidence output of the comparison means, and a control means for incrementing or decrementing the program counter according to the coincidence output of the comparison means. A microcomputer with a test circuit characterized in that it performs inspection without outputting to the computer.