Lecture 10: Synchronous Sequential Logic

Syed M. Mahmud, Ph.DECE Department

Wayne State University

Original Source: Aby K George, ECE Department, Wayne State University

Contents

• Introduction

• Sequential Circuits

• Storage Elements: Latches

• Storage Elements: Flip-Flops

• Analysis of Clocked Sequential Circuits

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Introduction

• Storing information

• Memory

• Operation and Control of these devices

• Their use in the circuits

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Sequential Circuits

• Combinational circuit with memory element in the feedback path.

• Storage elements can store binary information.

• A sequential circuit is specified by a time sequence of inputs, outputs, and internal states.

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Sequential Circuits

• Two types of sequential circuits• Synchronous

• Asynchronous

• Synchronous SC• The system behavior can be defined from the knowledge of its signals at

discrete instants of time.

• The synchronization can be achieved by clock generator

• Asynchronous SC• Depends upon the input signals at any instant of time and the order in which

the inputs change.

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Synchronous Clocked Sequential Circuits

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Storage Elements: Latches & Flip-flops

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Latches Flip-flops

Operate with signal levels Operate with clock signal transition

Level-sensitive Edge-sensitive

Not used in synchronous operations

Widely used in synchronous operations

Latches are the basic circuits

Latches are the buildingblocks of flip-flops

SR Latch

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D Latch

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Graphic Symbols for latches

Triggering

• Control input that changes the state of latch or flip-flop

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Master Slave D Flip-flop (Positive edge triggered)• When clock changes to logic-0, External data input D is transferred to

the output of the master.

• When 𝑐𝑙𝑘 = 1, slave is enabled, and master is disabled. Hence, the output will be 𝑄 = 𝑃

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S-R Flip-flop

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J-K Flip-flop

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T- Flip-flop

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Summary

• What are the differences between latches and flip-flops

• How to design a S-R latch?

• How to design a D flip-flop?

• Define setup and hold time in a D flip-flop?

• What are the other flip-flops?

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Homework – 5 – Part a

• 5.2

• 5.4

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