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Unformatted text preview: shift operation. Detailed descriptions are provided for some critical scan design rules. TABLE 2.7 ± Typical Scan Design Rules Design Style Scan Design Rule Recommended Solution Tristate buses Avoid during shift Fix bus contention during shift Bidirectional I/O ports Avoid during shift Force to input or output mode during shift Gated clocks (muxed-D full-scan) Avoid during shift Enable clocks during shift Derived clocks (muxed-D full-scan) Avoid Bypass clocks Combinational feedback loops Avoid Break the loops Asynchronous set/reset signals Avoid Use external pins Clocks driving data Avoid Block clocks to the data portion Floating buses Avoid Add bus keepers Floating inputs Not recommended Tie to V DD or ground Cross-coupled NAND/NOR gates Not recommended Use standard cells Non-scan storage elements Not recommended for full-scan design Initialize to known states, bypass, or make transparent...
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- Spring '08