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Multiple Input Shift Register Channel Selector

IP.com Disclosure Number: IPCOM000123008D
Original Publication Date: 1998-Apr-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 1 page(s) / 36K

Publishing Venue

IBM

Related People

Douskey, SM: AUTHOR [+2]

Abstract

Selecting or blocking channels to a multiple input shift register (MISR) during logic built-in self-test (LBIST) testing or debug can be very useful for patching or debugging problems. Various levels of granularity suit different designs. The most expensive being an individual latch selector for each channel, and the least being a binary decode (or no selector at all).

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This is the abbreviated version, containing approximately 93% of the total text.

Multiple Input Shift Register Channel Selector

      Selecting or blocking channels to a multiple input shift
register (MISR) during logic built-in self-test (LBIST) testing or
debug can be very useful for patching or debugging problems.  Various
levels of granularity suit different designs.  The most expensive
being an individual latch selector for each channel, and the least
being a binary decode (or no selector at all).

      A single-bit mask register is the most costly design, but
allows the most granularity.  In this case, a single latch is created
for each channel feeding the MISR.  When the latch is set, the
channel is deselected.  Setting multiple latches allow multiple
channels to be  blocked.  Setting all latches would then block all
channels.

      A design using a binary decode would drop the latch count
requirements to the highest integer above the base 2 log of the
number of channels plus one (i.e. 62 channels would require 6
latches) to index  a single channel.  The plus one allows selecting a
channel for blocking  that does not exist to enable all channels.
This could have also been  accomplished with a separate latch.  Yet
another latch may be added switch the meaning of the decode to block
all but the selected channel.  The logic for a single selector is
shown in the figure.

      Note that while this second scheme is much reduced over the
original single latch per channel version, it allows only the
selection of a single,...