JPS6291872A - Testing circuit - Google Patents

Abstract

PURPOSE:To enlarge the degree of freedom to a test by placing a test exclusive ROM in a part of a testing circuit, so that a test sequence and the testing method of each part in a circuit to be tested can be changed optionally. CONSTITUTION:An input signal control circuit 11 controls the operation of a ROM 12 in accordance with an input signal inputted from an input terminal by following a test program. The ROM 12 is placed exclusively for a test, a prescribed part (usually, an address) is driven in accordance with the output signal of the circuit, and a prescribed signal is outputted. The output signal of the ROM 12 is inputted to a test signal generating circuit 13, and a test signal corresponding to the output of the ROM 12 is generated, and supplied to a circuit to be tested. Accordingly, by setting optionally the contents of the ROM 12, a signal waveform supplied to the circuit to be tested can be determined optionally.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention provides a method for determining whether the function of an IC is normal or not.
This relates to a test circuit provided in C.

[Conventional technology]

Conventionally, the test circuit built into an IC has been designed to be as small as possible compared to the overall size of the IC, and in order to reduce the cost of the IC, a test circuit 23 has been used as shown in FIG.
Input circuit 2, which was assumed and designed at the design stage, is
1 and a control circuit 22, a design-through testing method;
The circuit configuration was such that it could only be tested in sequence.

[Problem that the invention seeks to solve]

The conventional test circuit described above has almost no freedom in testing, and the drive signal waveform of a given circuit under test inside the IC is determined based on the actual number of defective parts of the IC, defective test items, etc. It is quite difficult to change this, and to a certain extent it was possible only by recombining the program that determines the order in which test circuits are operated.

[Failure to solve the problem]

The test circuit of the present invention is a test-dedicated R (JM (
The circuit is configured such that the drive signal for a given circuit under test can be changed from time to time according to the output state of this R (JM), and the test order of each part of the circuit under test can be changed.

Of the conventional test circuits, the main test control circuit is a program ROM such as EPROM, EEPROM, etc.
Alternatively, the degree of freedom in testing can be increased by replacing the ROM with a MASK ROM or other ROM whose contents can be changed by hardware.

〔Example〕

FIG. 1 shows a circuit configuration showing one embodiment of the present invention.

11 is an input signal control circuit, and 12
Controls the operation of the ROM. 12 is a ROM placed exclusively for the last, and a predetermined portion (
address) is driven and outputs a predetermined signal.

The output signal of the ROM 12 enters a test signal generation circuit 13, where a test signal corresponding to the output of the ROM 12 is generated and supplied to the circuit under test.

Therefore, depending on the content of the ROM 12 being arbitrarily set, the test signal waveform supplied to the circuit under test can be arbitrarily determined.

〔Effect of the invention〕

As explained above, the present invention is characterized in that a test-dedicated ROM is placed in a part of the test circuit, and by changing the contents of this ROM, the signal waveform that drives the circuit under test can be changed.
It is possible to arbitrarily change the testing order, testing method, etc. of each part in the circuit under test.

Therefore, in the past, for example, the only way to improve deficiencies in test content was to rewrite the test program, but with the present invention, if the content of the test-specific ROM can be changed, there is 15 more room for testing. This dramatically reduces the degree of freedom for testing, and can be expected to have a significant effect on improving test quality. In the future, it is expected that testing of larger-scale ICs will become more and more difficult, and in the current situation where the N requirement for testing increases, there will be a demand for the test circuit of the present invention. I think so.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention, and FIG. 2 is a conventional test circuit. 11.21... Input signal control circuit, 12...
・Test-only ROM, 13...Test signal generation circuit, 14, 23...Test circuit, 22...
...Test control and signal generation circuit. Agent Patent Attorney Susumu Uchihara t' Kaya 2 Figure

Claims (1)

[Claims] In the test circuit built into the IC to test whether the IC is a good product or not, an RO is installed exclusively for testing.
A test circuit characterized by having M.