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# Structural and Functional use of Constant Values

IP.com Disclosure Number: IPCOM000089770D
Original Publication Date: 1977-Dec-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 4 page(s) / 61K

IBM

## Related People

Bahnsen, RJ: AUTHOR [+2]

## Abstract

Introduction. Verification of a logic network design by means of Boolean comparison is usually preceded by a structural analysis and segmentation process. The purpose of this analysis and segmentation is to: 1. produce a combinatorial model for the Boolean comparison program, and . 2. reduce the size of the model that is processed by the Boolean comparison program. This small model containing only those blocks required for checking a single output is called a segment.

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Structural and Functional use of Constant Values

Introduction.

Verification of a logic network design by means of Boolean comparison is usually preceded by a structural analysis and segmentation process. The purpose of this analysis and segmentation is to: 1. produce a combinatorial model for the Boolean comparison program, and . 2. reduce the size of the model that is processed by the Boolean comparison program. This small model containing only those blocks required for checking a single output is called a segment.

Typically, this structural analysis is performed without using the logic functions of the blocks in the network. Only the block interconnections are examined. The procedure to be described here uses block functions and constant values of 0 or 1 imposed at certain nets to obtain desirable transformations of the logic network description. Algorithm.

In the following description we assume that a functional variable table is given which indicates: 1. the nets that are to be considered as functional variables, 2. the nets that are tied to constant 0, and 3. the nets that are tied to constant 1.

The procedure is as outlined in the following steps. 1. Impose the constant values as dictated by the functional variable table. 2. Propagate the constant values forward as far as possible. For example, if any input to an AND block is 0, its output becomes 0. This constant value is then propagated ahead to the driven blocks, and so on. Similarly, if all inputs to an AND block are 1, its output becomes 1. This constant value is also propagated forward. Other logic functions are handled in the appropriate manner.

3. After all constant values have been propagated forward, perform segmentation by back tracing from a desired net. The back trace stops at nets having any of the following prop...