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Introduction

Welcome to the course pages for the Web-based version of EET 3350. This four semester credit hour course covers the principles and applications of digital systems, primarily those involving sequential circuits. Special attention is given to the formal analysis and design procedures for synchronous sequential logic circuits and bistable memory devices. Design projects focus on top-down design methodology using CAD tools and the VHSIC hardware description language.

To be successful in this course, you should have taken a course in the fundamentals of digital logic and circuitry (such as EET 2210). Such a course will have included a coverage of number systems, Boolean algebra, logic simplification, Karnaugh maps, logic gates, and simple (SSI/MSI) combinational logic circuitry such as adders, multipliers, multiplexers and decoders.

In addition, an introduction to the components used in sequential logic circuits is useful but not essential. Topics covered may have included an introductory discussion of flip flops, counters, shift registers, memory devices, programmable logic devices and integrated circuits. Many of these topics will also be covered as part of this course, but in greater depth.

Some Definitions

To provide some perspective as to where this course fits in the curriculum, a few basic definitions are necessary.

Combinational Logic. The figure below illustrates a generalized combinational logic circuit, showing that it can have any number of inputs and any number of outputs. The number of inputs and outputs need not be the same. As a formal definition, "a combinational logic circuit is one where the next output depends only on the current input." Thus, for the output to change, the input must change. Also, a specific set of inputs always leads to the same output. The box labeled "Combinational Logic" is a circuit composed of basic logic gates (e.g., AND, OR, NAND, NOR, NOT).

Sequential Logic. In a similar manner, the formal definition of a sequential logic circuit is one where "the next output depends not only on the current input but also on the sequence of past inputs." In other words, sequential logic circuits are circuits whose output values depend on the sequence of input values applied with respect to time. Clearly, some memory of this past history of input values is required. The diagram above shows a generalized sequential logic circuit. It differs from the combinational logic circuit in that it includes both a combinational logic block and a memory block. Typically, the memory block of a sequential logic circuit is constructed using one or more flip flops.

State. As used above, the term "state" has special meaning. A digital logic state is the logic value of a gate or circuit output. For a single output circuit this is the binary value of zero or one (0 or 1). For a multiple output circuit, the state is the ordered binary representation of the collection of output values at a specific instant in time. For example, a two-output circuit would have four possible states: 00, 01, 10 and 11. In the generalized sequential logic circuit diagram shown above, the state would be represented by the collection of all output values from the combinational logic block ... including both output values and next state values.

The Content of EET 3350

In this course we assume that you are familiar with the building blocks for combinational logic circuits and the procedures for designing mimimal realizations of these circuits. The focus of this course will be on the building blocks for sequential logic circuits (primarily flip flops) and procedures for the analysis and design of sequential logic circuits.

Although the focus of this course is on sequential logic circuits, you will not be able to ignore what you have learned about combinational logic circuits. As the diagram below should indicate, everything above the red dashed line is still a multiple-input multiple-output combinational logic circuit. Thus, the design of a sequential logic circuit includes the design of a combinational logic circuit.

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