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Logic Built-In Self-Test 267 all scan design rules and BIST-specific design rules, called BIST design rules . The process of taking a scan-based design and making it meet all additional BIST-specific design rules turns the design into a BIST-ready core. 5.2.1 Unknown Source Blocking There are many unknown (X) sources in a CUT or BIST-ready core. Any unknown (X) source in the BIST-ready core, which is capable of propagating its unknown (X) value to the ORA directly or indirectly, must be blocked and fixed using a DFT repair approach often called X-bounding or X-blocking . Figure 5.3 shows a few of the more typically used X-bounding methods for blocking an unknown (X) source: The 0-control point forces an X source to 0; the 1-control point controls the X source to 1; the bypass logic allows the output of the X source to receive both 0 and 1 from a primary input (PI) or an internal node; the control-only scan point drives both 0 and 1 through a storage element, such as D flip-flop; and, finally, the scan point can capture the X-source value and drive both 0 and 1 through a scan
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This note was uploaded on 05/16/2011 for the course ENGINEERIN mp108 taught by Professor Elbarki during the Spring '08 term at Alexandria University.

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