Synchronization and Arbitration in Digital Systems

1

Synchronization, Arbitration and Choice

1.1 INTRODUCTION

Digital systems have replaced their analog counterparts in computers, signal processing and much of communications hardware at least partly because they are much more reliable. They operate in a domain of absolutes where all the data moving from one place to another is quantized into defined high or low voltages, or binary coded combinations of highs and lows. The great advantage of this is that the data represented by the voltages can be preserved in the presence of small amounts of noise, or variations in component or power supplies, which can affect the voltages. A small variation in a high is still easily distinguished from a low, and a simple circuit, such as a gate or an inverter, can easily restore the correct output level.

In a synchronous system the signal states are also held by flip-flops when the clock ticks. Clocking digitizes time into discrete intervals of time, which are multiples of the clock cycle, with data computed during the first part of the cycle, and guaranteed correct on the next clock rising edge. Small variations in the time taken to evaluate a partial result have no effect on a correctly designed digital system, the data is always correct when it is next clocked. This discipline of two discrete voltage levels and time measured in multiples of the clock period allows most digital components to operate in a controlled environment, provided their outputs do not vary by more than a certain amount ...