Digital Design - Logic, Memory, Computers

Electrical and Electronic Engineering Design Series Volume 3

This university level Electrical Engineering text is for anyone who wants to know how to design products using digital logic circuits. The present text is unusually accessible to readers who want to acquire the skills of digital design. We present a thorough foundation so that you can proceed to learn how to design any digital system.

This text is different from the many introductory digital design texts, because we actually design a product by implementing a design and not just talk about logic circuits used in a digital circuit. And, we ask you to work hard doing experiments so that you acquire real world experience with commercially available digital circuits. In other words this is about real learning.

We start at the beginning by presenting a top down design method for digital systems.

We learn about three basic tools necessary to execute any digital design - Truth Tables, Karnaugh maps, and Switching Algebra.

The basic circuits of digital logic are building blocks without memory. They are standard commercially available logic circuits, which are described and their equations are presented. We only use standard products. Furthermore we show how to use mixed logic that simplifies digital design.

The ASM (algorithmic state machine) chart, a fourth tool, is the preferred way to implement the algorithm representing the product you want to design. We show how to implement ASM charts, derive truth tables from them, and how to convert the truth tables to digital circuits. The ASM-chart-to-product process is straightforward.

The design of complex building blocks with memory is based on elementary blocks with one bit memory also known as flip-flops. Designs are implemented by the ASM method. We show how to use ASM’s to design up and up/down synchronous counters, shift registers, and linear feedback shift registers using standard products.

This is followed by showing how to design memory systems with and without a cache hierarchy. We explain, and then show how to add error correction and control to the memory system. ASM charts and associated timing diagrams allow us to readily implement the designs. These are charts and timing diagrams we have not found anywhere else.

A computer has two basic parts – computer control and a datapath for executing instructions. We define a user instruction set (uI), the uI address modes, and how the uI are formatted as binary words. Status bits NCZV and their condition codes that implement program control are defined. We show how each uI is represented by a list of micro instructions mI that is executed by the datapath, and how the datapath executes the mI.

For large circuit designs text capture of digital designs is preferred to schematic capture. Verilog uses text capture to represent digital circuits with a hierarchy of modules that are interconnected via input and output ports. We show by example how to write modules defining digital circuits so that you can move on to multi 1,000 gate chip designs using Verilog, which is a hardware description language (HDL).

The presentations are eminently clear, because they are based on the policies assume nothing and nothing is obvious.

The present text's contents are topics one actually uses when engaged in digital circuit analysis and design.

Eight experiments are included that give life to the text’s contents, and provide the reader with real world experience with making measurements, using instruments, and learning about all kinds of parts. We consider the experiments to be significant learning activities.