Browse Prior Art Database

Production Signature Analysis Diagnosis with Relaxed Design Constraints

IP.com Disclosure Number: IPCOM000048126D
Original Publication Date: 1981-Dec-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 4 page(s) / 63K

Publishing Venue

IBM

Related People

Zobniw, LM: AUTHOR

Abstract

A self stimulating signature Analysis (SA) testing approach offers the opportunity to examine a card under test (CUT) at real time speed and with a less costly hardware tester, as compared to the sophisticated functional speed testers with high speed programmable buffers. The SA testing approach is tailored to test cards designed with functional devices, i.e., microprocessors and microprocessor related devices, that require functional speed testing. SA does not replace the need for functional speed testers especially to test asynchronous "random logic" card designs. However, for many card designs, the described production SA testing approach can be used to free the costly functional testers for cards that require them.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 35% of the total text.

Page 1 of 4

Production Signature Analysis Diagnosis with Relaxed Design Constraints

A self stimulating signature Analysis (SA) testing approach offers the opportunity to examine a card under test (CUT) at real time speed and with a less costly hardware tester, as compared to the sophisticated functional speed testers with high speed programmable buffers. The SA testing approach is tailored to test cards designed with functional devices, i.e., microprocessors and microprocessor related devices, that require functional speed testing. SA does not replace the need for functional speed testers especially to test asynchronous "random logic" card designs. However, for many card designs, the described production SA testing approach can be used to free the costly functional testers for cards that require them.

In general, the stimuli (for SA) are generated by the microprocessor and ROM (read only memory) circuitry that are on the CUT, on the tester, or on both the card and tester. The responses, from primary net, are shifted into SA circuitry, such as shown in Fig. 1. At the end of the test sequence, the contents or signature in the 16-bit shift register is compared with a known good signature to determine whether the card passed or failed.

The literature on SA provides guidelines on the use of this technique. The Signature Analyzer compresses a string of response values (logic 1, 0) into a signature, i.e., a distinct 16-bit number usually written in hexadecimal form. The probability is very low that a bad signature will equal the good signature for the monitored node. SA must be designed into the CUT. For example, the designer should insure that the feedback loops are opened, electrically or physically during SA test. If the feedback loops between modules are not opened, then every net along the loop will exhibit a faulty signature and it will not be possible to identify the faulty module. It is also recommended to disable bus elements, forming a dot, during SA fault tracing.

Some of the key SA advantages are: inexpensive test hardware, diagnostic approach usable in the field, and the tests are run at functional or real time speeds. A key SA limitation is the requirement that components be physically isolated via switches or jumpers to break feedback loops. This SA restriction requires that everything run open loop and with minimum interaction between portions within a functional loop. This article describes an approach for providing SA type testing in production test mode that does not require physical loop breaking and illustrates approaches to create the test data.

Existing SA approaches can only indicate that the net failed during the test sequence. It cannot indicate when the failure was first detected. With the additional knowledge of "when" in the test sequence the net failed, the fault may be isolated even along the failing loop and the SA physical loop breaking requirement may be relaxed or eliminated. This approach is tailored to the produc...