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.
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.
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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