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# Analysis and Synthesis of Synchronous Sequential Circuits - PowerPoint PPT Presentation

Analysis and Synthesis of Synchronous Sequential Circuits. A “synchronizing” pulse/edge signal (clock) controls the operation of the memory portion of the circuit When no clock – the circuit is asynchronous:. Analysis and Synthesis of Synchronous Sequential Circuits.

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• A “synchronizing” pulse/edge signal (clock) controls the operation of the memory portion of the circuit

• When noclock – thecircuit is asynchronous:

• The “state” of a synchronous sequential circuit:

• All the FF/memory element outputs

• Can change only upon clock transition (pulse/edge)

• Two models for synchronous sequential circuits:

• Mealy model

• Outputs are a function of state and inputs

• Moore model

• Outputs are a function of state only

• Next state (Y1,…,Yr) achieved on clock transition

• Input (x1,…,xn), output (z1,…,zm), present state (y1,…,yr) and next state (Y1,…,Yr) are

where gi and hi are Boolean functions, or in vector form

x1

xn

Combinational logic

Y1

Yr

Memory

y1

yr

clock

Combinational logic

z1

zm

• State diagram and state table

• Assumes  transitions

Problem?

• State diagram and state table

• Output is f(state) only

• Inputs – no effect

• Representations can be transformed into each other

• Advantages and disadvantages

Mealy Moore

- glitches + no glitches

- problem sampling

+ easier to design

+ lesser total # states

• Analysis of logic diagrams of sequential circuits

• Inputs, state variables, outputs, logic equations ?

• Mealy or Moore type?

• Input sequence: x = 01101000

• Deriving state diagram and state table

• Given circuit diagram  Boolean equations

• Notation: yk represents y(k t)

• k = integer; t = clock period

• May assign numbers to states: 0  state A; 1  state B

• Deriving state table from K-maps

Map for Yk=yk+1

Map for zk

• Synchronous sequential circuit with flip-flops

• Negative edge-triggered

• Inputs?

• States?

• Outputs?

• Logic equations?

• Timing diagram

• State table and K-maps

• Combining the K-maps into state table