7d_State_Assignment_Slides

7d_State_Assignment_Slides - ECE ECE 3504 Digital Design 1...

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ECE 3504 Digital Design 1 Section 7d: State Assignment
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Asynchronous Design Procedure I. Parse the specification. Since there is no clock, the Mealy-Moore distinction doesn’t apply. II. Model the system using a primitive flow table III. Reduce the primitive flow table to one having a minimal number of states. A. Use the General Incompletely Specified Method. B. Use the Two-Step Method. IV. Make a state assignment that is free of critical races. A. Introduce cycles using the Ad-Hoc Method. B. Use a Universal State Assignment. V. Implement the circuit A. Assign outputs to unstable states to avoid glitches. B. Design the combinational logic to prevent hazards.
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State Transition State Transitions Recall the requirement that only Recall the requirement that only one state variable may change as the result of a single state ti t i transition. To see the problems that result when violate this requirement, consider a certain state table for which a designer has made an arbitrar state assignment arbitrary state assignment.
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State Assignmen State Assignment 1 2 PS x x 00 01 11 10 1 c 3 cc 2–3 d 4 31 eee 4 f 32 f y 1 y 2 x 1 x 2 00 01 11 10 00 (1) 00 11 00 00 01 (2) 11 01 10 11 (3) 00 11 11 11 10 (4) 10 11 01 10
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Races and Critical Race Races and Critical Races A race condition describes a state A describes a state change where more than one state variable must change at the same ti t t th t th t time to guarantee that the correct state change will occur. A critical race describes a race where at least one of the ways in which the race could settle is an incorrect stable state incorrect stable state.
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Races and Critical Race Races and Critical Races In order for a transition to a given In order for a transition to a given input column to result in a critical race, there must be at least two tb l tt i tht l stable states in that column. If there is only one stable state in a column, then even if a race condition exists, all unstable states will still point to that stable state.
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7d_State_Assignment_Slides - ECE ECE 3504 Digital Design 1...

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