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U. Glaeser

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FIGURE 46.7<br />

generate tests for every fault and then the test patterns, which are selected, are those which necessitate<br />

the fewest number of flip-flops that are scanned.<br />

Scan and Built-in Test Solutions<br />

A scan design can serve as a support for a complete built-in-test solution. Indeed, as assumed earlier (see<br />

Fig. 46.2), test patterns are supposed to be generated from outside and applied through the Sin pin.<br />

Furthermore, it is assumed that test results are scanned out through the Sout pin and compared one by<br />

one to the test results of a golden circuit. A golden circuit is a circuit, which is assumed to be fault-free.<br />

A scan-based design can be used in order to implement both test pattern generation and test result<br />

verification functions within the DUT. Built-in-Self-Test (BIST) is a design-for-testability technique in<br />

which testing (test generation and test application) is accomplished through built-in hardware features<br />

[5–6]. When testing is built as a hardware it is very fast and very efficient.<br />

The example in Fig. 46.7 shows how a basic scan design is considered for a BIST solution. The LFSR<br />

(linear feedback shift register) is used as an example of a test pattern generator. Pseudo-random test<br />

patterns, which can be very efficient in case of sequential designs, are generated using such a structure.<br />

For test results verification, a LFSR is used to compress test results and produce a signature which will<br />

represent the obtained test results.<br />

Tools and Languages for Scan Automation<br />

Today, several CAD vendors include BS in their DFT test tool (Mentor Graphics, Teradyne, Jtag Technologies,<br />

Logic Vision, etc.). Tools which are available in the market propose scan testing solutions. The<br />

main functions that are proposed by such tools are: scan design rules checking, scan conversion, and the<br />

associated test pattern generation.<br />

Through the IEEE standard 1149.1-1990, the BS technology is more and more embraced in electronic<br />

systems at several hierarchical levels: ICs, boards, subsystems, and systems. One of the key points that has<br />

helped in that is the availability of tools and languages that support such a technology. A subset of VHDL<br />

was proposed for this purpose [13]. The language is called BSDL (boundary scan description language).<br />

When a new standard is proposed many barriers may slow down its adoption. BSDL was proposed in<br />

order to speed up the implementation of the “dot one” standard through BSDL-based tools. This language<br />

helps in the description and the checking of the compliance of a design with BS technology. More precisely,<br />

BSDL helps in the implementation of testability features, which are related to the “dot one” technology.<br />

Hence, necessary simulation and verification of the BS technology can be performed. More precisely,<br />

testing if a DUT is compliant with the “dot one” technology means that devices that are mandatory to<br />

be implemented are checked. For example, the parameters that related to the TAP controller and the<br />

boundary scan register are described and checked out through such a language. Furthermore, BSDL serves<br />

as a support for IC vendors to automatically add BS logic through all design process of the design.<br />

More information about BSDL can be found in [13].<br />

© 2002 by CRC Press LLC<br />

LFSR<br />

test pattern<br />

generation<br />

LFSR<br />

test result<br />

compression<br />

Example of merging scan and BIST.<br />

SIN<br />

SOUT<br />

Scan register SRI<br />

· ·<br />

·<br />

CUT<br />

· ·<br />

·<br />

Scan register SR0

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