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Boundary Scan Design for Functional Clocks

IP.com Disclosure Number: IPCOM000102112D
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 3 page(s) / 73K

Publishing Venue

IBM

Related People

Douskey, SM: AUTHOR [+3]

Abstract

Boundary scan can be added to a design such that the benefits of internal AC random pattern self-test and external interconnect test are possible, while retaining the stuck fault testability. Through maintaining the L1 - L2 - L1 path arrangement, even at the boundaries, use of functional clocks for AC testing is allowed. Also, by conscientiously designing the boundary scan latches, stuck fault testability can be maintained.

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Boundary Scan Design for Functional Clocks

       Boundary scan can be added to a design such that the
benefits of internal AC random pattern self-test and external
interconnect test are possible, while retaining the stuck fault
testability.  Through maintaining the L1 - L2 - L1 path arrangement,
even at the boundaries, use of functional clocks for AC testing is
allowed.  Also, by conscientiously designing the boundary scan
latches, stuck fault testability can be maintained.

      Level-Sensitive Scan Design (LSSD) is used in many systems
throughout the industry.  The boundary scan design described here is
based on LSSD.  Also common in large systems is the use of two system
clocks throughout the design.  This arrangement is assumed for
illustration (however, this scheme can also apply to multiple clock
designs).

      Fig. 1 shows a simple chip boundary condition before the
addition of boundary scan.  Note that the driver (signal source)
comes from an L2 and the receiver feeds an L1.  This is the dominant,
if not only, I/O arrangement in the design. Also realize that most
signals are much more complex. Drivers are fed from multiple L2s
through combinatorial logic and receivers fan out through logic to
many L1s.

      Figs. 2 and 3 show the double latch set up for the two types
of boundary scan I/O.

      Fig. 2 shows the most used boundary scan book: the Common I/O.
The driver is fed by a boundary scan L1.  This L1 is fed by data
from internal to the chip. ...