Digital Logic Testing and Simulation, 2nd Edition

CHAPTER 10

Memory Test

10.1 INTRODUCTION

Memory is pervasive in digital products. Consider, for example, the personal computer (PC). It has main memory, video memory, translation ROMs, shadow ROMs, scratchpad memory, hard disk, floppy disk, CDROM, and various other kinds of storage distributed throughout. In addition, the die that contains the microprocessor may also contain one or more levels of cache.

A typical PC is depicted in the block diagram of Figure 10.1. It is basically a memory hierarchy connected by several buses and adapters and controlled by a CPU. The purpose for much of the hierarchy is to combine two or more storage systems with divergent capacities, speeds, and costs such that the combined system has almost the speed of the smaller, faster, more expensive memory at almost the cost, speed, and storage capacity of the larger, slower, less expensive memory. Clearly, not all storage devices are part of this hierarchy. The CDROM may be used to deliver programs and/or data to an end user, and video memory is dedicated to the display console. The central processing unit (CPU) accesses many of these auxiliary memory devices through a peripheral component interconnect (PCI) bus, which regulates the flow of data through the system.

Unlike the random logic that has been considered up to this point, memory storage devices are characterized by a high degree of regularity. For ...