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Method and Mechanism to Efficiently Initialize Latches that are not part of a Scan Chain (Non-Scan Latches) Disclosure Number: IPCOM000020286D
Original Publication Date: 2003-Nov-10
Included in the Prior Art Database: 2003-Nov-10
Document File: 1 page(s) / 5K

Publishing Venue



Some latches in a chip are non-scanable, need nethertheless to be initialized. The disclosure below shows how to initialize such latches to a fix value with no additional signals than the one required for scanning scan latches.

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  Method and Mechanism to Efficiently Initialize Latches that are not part of a Scan Chain (Non-Scan Latches)

  In a chip some latches may not be scanned since this would disrupt the scanning process or disrupt normal operation of other parts of the running chip. For example, a latch that holds scan chain configuration data must not be part of a scan chain because otherwise the configuration would change during scanning. Nevertheless these latches need to be initialized to some defined values at power-on or after latch initialization of the chip. For latches in a scan chain, this is usually done by scanning a static value through the chain. Obviously, initializing latches that are not part of a scan chain is not possible this way.

    The present publication manages to initialize non-scannable latches without the need of a global reset or init signal and thereby omits the associated wiring and timing problems.

    The present publication takes advantage of the fact that in a LSSD design, usually all latches have the inputs and outputs that are required for scanning, although they might be unused if the latch is not part of a scan chain. The presented mechanism does not need the data input pin data in (see picture below) of the latch to be deterministic at initialization time as required in the second case described above:


initialization value (scin)

data in


    The scan input scin of the latch is tied to the initialization value. When the scan clock sc1 is applied, the la...