Browse Prior Art Database

Method to Allow Variable Scan Chain Lengths for Register Arrays

IP.com Disclosure Number: IPCOM000118796D
Original Publication Date: 1997-Jul-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 2 page(s) / 66K

Publishing Venue

IBM

Related People

Aipperspach, AG: AUTHOR [+2]

Abstract

Disclosed is a method of creating variable-length scan chains through scannable arrays or other large macros.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 74% of the total text.

Method to Allow Variable Scan Chain Lengths for Register Arrays

      Disclosed is a method of creating variable-length scan chains
through scannable arrays or other large macros.

      Typically, scannable arrays have been designed with a small
number (1 or 2) of relatively long-scan chains.  Fig. 1 shows how the
scan chain might look in such an array, with a single scan chain from
the Scan Data In (SDI) pin to the Scan Data Out (SDO) pin.  It also
shows where the latches might physically appear in an array.

      The array scan chains can be made configurable by creating many
very small scan chains, as shown in Fig. 2.  This allows the small
scan chains to be connected up in groups to give scan chain lengths
that are desired.  There is typically a range of scan chain lengths
that are acceptable at the chip level, and the length of the array's
small scan chains should be less than the size of this window in
order to always be able to meet the requirements.

      An array can be given these small scan chains without creating
a wiring problem on the chip.  Note that in Fig. 2, each scan in is
right next to the previous scan out, such as SDI(1) and SDO(0).
Whenever a connection is made between these pins, it should use local
wiring, without any impact to the rest of the chip.  When scan chain
groups are  created, consecutive chains of the array will be used to
make use of as  many of these direct connections as possible.  Only
the scan pins that ...