Browse Prior Art Database

Don't Care For Boolean Analysis

IP.com Disclosure Number: IPCOM000050353D
Original Publication Date: 1982-Oct-01
Included in the Prior Art Database: 2005-Feb-10
Document File: 2 page(s) / 33K

Publishing Venue

IBM

Related People

Bahnsen, RJ: AUTHOR [+4]

Abstract

If the "don't care" logic in the figure is ignored, the figure shows the form of logic generally used to verify that the combinatorial logic driving a pair of corresponding Storage Elements or Primary Outputs is Boolean equivalent. Model 1 is the combinatorial logic from the first design, and Model 2 is the combinatorial logic from the second design. If (and only if) the function of Model 1 differs from that of Model 2 in the Boolean sense, then there must be at least one state of the inputs which gives a one on output p or output q. Each such state of the inputs constitutes a counter example.

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Don't Care For Boolean Analysis

If the "don't care" logic in the figure is ignored, the figure shows the form of logic generally used to verify that the combinatorial logic driving a pair of corresponding Storage Elements or Primary Outputs is Boolean equivalent. Model 1 is the combinatorial logic from the first design, and Model 2 is the combinatorial logic from the second design. If (and only if) the function of Model 1 differs from that of Model 2 in the Boolean sense, then there must be at least one state of the inputs which gives a one on output p or output q. Each such state of the inputs constitutes a counter example.

In order to preclude the generation of unwanted counter examples (e.g., counter examples which define unreachable states of the machine), additional Boolean logic, called the "don't care" logic, is provided to define the states for which no counter examples are wanted; i.e., the user does not care about the results. The "don't care" logic is based on some subset (perhaps, a proper subset) of the input variables to Model 1 and Model 2. (Other inputs may be included, but in general the "don't care" becomes degenerate except in unusual cases.) The "don't care" is defined such that it is one for "don't care" conditions. The effect of the form shown in the figure is to prevent either of the outputs p and q from achieving a value of one for any state of the machine for which the user does not care. Therefore, all counter examples produced necessari...