Browse Prior Art Database

TESTABLE MULTIPLIER ARRAY DESIGN IN THE FLOATING POINT OF MICROPROCESSORS

IP.com Disclosure Number: IPCOM000007998D
Original Publication Date: 1997-Mar-01
Included in the Prior Art Database: 2002-May-10
Document File: 2 page(s) / 102K

Publishing Venue

Motorola

Related People

Romesh M. Jessani: AUTHOR [+3]

Abstract

Multiplier arrays are designed as regular itera- tive arrays which include Booth encoders, Booth muxes and carry save adders' (CSA). Uncontrolled constants feeding into the multiplier array results in untestable circuits within the Booth mux and CSA circuits. This invention provides a high test cover- age for multiplier arrays.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 50% of the total text.

Page 1 of 2

m MOTOROLA Technical Developments

TESTABLE MULTIPLIER ARRAY DESIGN IN THE

FLOATING POINT OF MICROPROCESSORS

by Romesh M. Jessani, Kofi Vida-Torku and Craig Hunter

1 .O FIELD OF THE INVENTION

  Multiplier arrays are designed as regular itera- tive arrays which include Booth encoders, Booth muxes and carry save adders' (CSA). Uncontrolled constants feeding into the multiplier array results in untestable circuits within the Booth mux and CSA circuits. This invention provides a high test cover- age for multiplier arrays.

2.0 BACKGROUND OF THE INVENTION

  Wallace tree multiplier arrays involve Booth encoding of the multiplier operand. These are used to mux-select one of various versions of the multi- plicand (A) to obtain partial products, which are added to obtain the final result. Any tied inputs to the multiplier array should be controllable. For a 3- bit Booth encoding, the partial product is one of O*A, l*A, 2*A, -l*A and -2*A. The Booth muxes involves inputs which are constants due to the term O*A (all Booth encoding involve the O*A term). Moreover, in the CSA tree structure, the displace- ment of one partial product with respect to the pre- vious partial product introduces further constants in the array. The testability of the multiplier array decreases due to the constant applied to any term of the multiplier array, since test vectors can't be applied to the constant inputs of individual cells.

  Moreover, when Booth Muxes and CSAs are designed with pass gate muxes, stuck-at faults in the logic networks of these CSA's must be propa- gated through several stages of Three State Drivers (TSD). Test generators are unable to navigate through the several layers of TSD drivers to detect the faults.

3.0 SUMMARY OF THE INVENTION

The objective of the present invention is to pro-

vide high test coverage for multiplier arrays, using control points to pulldown or pullup the tied off inputs to the Booth muxes and CSAs. These control points can be driven by latches or by other test con- trol devices.

4.0 DESCRIPTION OF THE INVENTION

  The invention consists of using three extra pullup/pul...