Embedded test standards effectively began with the 1149.1 standard, developed to handle increasingly complex digital parts. Test engineers found it more and more difficult to understand how the parts worked well enough to propagate test patterns, and then develop functional tests economically. Test engineers just lack the flexibility that design engineers possess. Test development must occur in a small fraction of the time that it takes to design the product.
The 1149.1 standard provided a way to test device interconnectivity and functionality independent from the function of the device itself. It enables a standard description of the device boundary and offers a standard method for invoking and gathering the results of built-in self tests. With 1149.1, the test engineer no longer needs to understand device function and can deploy tests with excellent test coverage. IEEE Standards 1149.4 and 1149.6 embedded test standards are based on this foundation.
More extensions of embedded test standards are certain to appear as test needs arise. These test methods are proving to be very cost effective at both the chip and board level compared to alternatives. We will also see the test framework used for purposes other than testing, as has already occurred in the 1500 standard for programmable devices. Such dual use makes the built-in test structures nearly free.
The largest obstacle in developing an embedded test standard is predicting how technological changes will help the standard rather than make it obsolete. For example, the approximately 7500 switches used in an in-circuit tester will now occupy about 15,000 µm2 of the chip's surface. More significantly, testing the functions on and around a single chip requires much less resources than the largest board, which an in-circuit tester can test.
Definition of a standard requires the collective wisdom of many companies and a significant amount of consensus building. Technology demonstration and consensus building take more time than technology changes, making it imperative that the standard not rely on a technology that can change tomorrow.
The bottom line is that embedded testing significantly reduces test-hardware costs. This was vividly demonstrated by a demo that a group of companies performed last January. It can be seen at http://www.fe.up.-pt/~allegro/wp3/d3x_wbm/-Mod6/remote_-ieee_1149.htm.
