Browse Prior Art Database

Chip Scan-Flush Initialization during a Functional System Reset

IP.com Disclosure Number: IPCOM000112847D
Original Publication Date: 1994-Jun-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Cohen, M: AUTHOR [+6]

Abstract

Disclosed is an innovative way to fully initialize a Level-Sensitive Scan Design (LSSD) by scan-flushing logic during a synchronous system reset. The scheme disclosed involves by-passing the functional logic path and making use of the LSSD scan circuitry to initialize latches.

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Chip Scan-Flush Initialization during a Functional System Reset

      Disclosed is an innovative way to fully initialize a
Level-Sensitive Scan Design (LSSD) by scan-flushing logic during a
synchronous system reset.  The scheme disclosed involves by-passing
the functional logic path and making use of the LSSD scan circuitry
to initialize latches.

      LSSD latches are sourced by the following clocks and test
signals:  FUNCTIONAL_C_CLK/FLUSH_OFF,  TEST_SCANIN/FLUSH_0,
TEST_A_CLK/ FLUSH_ON and FUNCTIONAL_B_CLK_FLUSH_ON,  which  are
generated by the  circuit shown in Fig. 1.

The Scan Path Flush Initialization Sequence Follows (Refer to Fig.
2):

1.  A leading synchronous system reset is generated during DLY1.

2.  DLY1 ns after the start of a SYSTEM_RESET,
    FUNCTIONAL_C_CLK/FLUSH_OFF is turned off.  This signal feeds the
    C_CLK inputs into  the LSSD latches, hence, the data inputs to
    these latches are not sensed then.

3.  The scan input to LSSD latches,  TEST_SCANIN/FLUSH_0, is forced
    to a logical '0'.

4.  The A (TEST_A_CLK/FLUSH_ON) and B (FUNCTIONAL_B_CLK/FLUSH_ON)
    clocks to the LSSD latches are asserted, thus flushing a '0'
    through the LSSD scan path.

5.  What is essentially a clock chopper circuit creates a pulse of
    width DLY2 which ensures that the longest scan path is traversed
    and all latches are initialized to a '0' value.

6.  (DLY1 + DLY2) ns after the start of SYSTEM_RESET, the functional
 ...