The foundations for the design of digital logic circuits were established in the preceding chapte... more The foundations for the design of digital logic circuits were established in the preceding chapters. The elements of Boolean algebra (two-element " switching algebra ") and how the operations in Boolean algebra can be represented schematically by means of gates (primitive devices) were presented in Chapter 2. How switching expressions can be manipulated and represented in different ways was the subject of Chapter 3, which also presented various ways of implementing such representations in a variety of circuits using primitive gates. With all of the tools for the purpose now in hand, we will be concerned in this chapter with the design of more complex logic circuits. Circuits in which all outputs at any given time depend only on the inputs at that time are called com-binational logic circuits. The design procedures will be illustrated with important classes of circuits that are now universal in digital systems. The approach taken is to examine the tasks that a combinational logic circuit is intented to perform and then identify one or more circuits that can perform the task. One circuit may have some specific advantages over others, but it may also have certain deficiencies. Often one factor can be improved, but only at the expense of others. Some important factors are speed of operation, complexity or cost of hardware, power dissipation, and availability in prefabricated units. We will take up a number of different operations that are useful in different contexts and show how appropriate circuits can be designed to carry out these operations.
The foundations for the design of digital logic circuits were established in the preceding chapte... more The foundations for the design of digital logic circuits were established in the preceding chapters. The elements of Boolean algebra (two-element " switching algebra ") and how the operations in Boolean algebra can be represented schematically by means of gates (primitive devices) were presented in Chapter 2. How switching expressions can be manipulated and represented in different ways was the subject of Chapter 3, which also presented various ways of implementing such representations in a variety of circuits using primitive gates. With all of the tools for the purpose now in hand, we will be concerned in this chapter with the design of more complex logic circuits. Circuits in which all outputs at any given time depend only on the inputs at that time are called com-binational logic circuits. The design procedures will be illustrated with important classes of circuits that are now universal in digital systems. The approach taken is to examine the tasks that a combinational logic circuit is intented to perform and then identify one or more circuits that can perform the task. One circuit may have some specific advantages over others, but it may also have certain deficiencies. Often one factor can be improved, but only at the expense of others. Some important factors are speed of operation, complexity or cost of hardware, power dissipation, and availability in prefabricated units. We will take up a number of different operations that are useful in different contexts and show how appropriate circuits can be designed to carry out these operations.
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